SYMPOSIUM B

2:00 PM *B3-S3.1 (invited)
Emerging Photonics Applications of Large, Flexible Arrays of Microcavity Plasma Devices. (#1423) J G Eden, Laboratory for Optical Physics and Engineering, Department of Electrical and Computer Engineering, University of Illinois Urbana, USA.

Microcavity plasma devices are a new class of hybrid plasma/optoelectronic device in which a non-equilibrium low temperature plasma is spatially confined to a microcavity with a characteristic cross-sectional dimension of nominally 10-200 ?m. Plasmas so confined are stable glows having nanoliter volumes and operating at gas pressures up to and beyond one atmosphere. Conventional mass production techniques can be used to fabricate arrays of microplasma devices having precisely-controlled microcavity dimensions and dielectric structures, thereby tailoring the electric field within the microcavity. This presentation will focus on novel microplasma devices realized recently, and the fabrication and performance of large arrays of microcavity plasma devices. Arrays as large as 900 cm² in radiating area with overall thicknesses < 1 mm have been demonstrated. Selected applications of these photonic devices in displays, illumination, and biomedical phototherapeutics will be discussed.

2:30 PM B3-S3.2
The Detached Solidifaction of Ga_1-xIn_xSb_{(x < 0.5)} bulk Single Crystal Grown by Vertical Directional Solidification Technique on the Earth. (#39) Dattatray Bhairu Gadkari, Brijmohan Arora; Department of Physics, Mithibai College, Mumbai, India.

IUMRS-ICEM-08 Symposium B: Com. Semi. Materials & Devices THE DETACHED SOLIDIFICATION OF Ga(1-) In x Sb (x < 0.5) BULK SINGLE CRYSTAL GROWN BY VERTICAL DIRECTIONAL SOLIDIFICATION TECHNIQUE ON THE EARTH D B Gadkari1 and B M Arora2 1. Department of Physics Mithibai College Mumbai 400056, India 2. CMP&MS Tata Institute of Fundamental Research Mumbai 500005, India E-mail:dr_gadkari@yahoo.com ABSTRACT: A vertical directional solidification (VDS) technique is applied to grow Ga(1-x) Inx Sb (x <0.5) bulk single crystals without seed and without contact to the ampoule. We have designed and fabricated furnace with special axial and radial temperature gradients with optimized growth parameters. It showed the stable condition can be reached for the growth of semiconductor crystals by this technique. Method of controlled growth of crystal conditions and parameters for detached solidification in ampoule is described. The goal is to develop gap for growing crystal in ampoule without influence of the hydrostatic pressure of the melt and to accomplish a melt meniscus between crystal-melt interfaces. Also the influence of hydrodynamic melt pressure is anticipated therefore a tiny melt is lowered down from the hot zone for constricted solidification. This effect is attributed as reduced radial temperature gradient on solidification under detached condition, and it is related with the steady state interface position, thermodynamic equilibrium. Grown crystals are characterized with outer ingot surface and interior substrate surface for macro and micro growth features. Electrophysical measurements of GaInxSb (x <0.5) are studied to know the enhancement in crystal quality. In comparison to attached grown ingots with that of detached a pronounced reduction in defects is investigated. The results of analysis of space (microgravity), centrifuge and ground experiments on detached growth of these crystals are studied for the influence of detachment on the growth, structure and properties of grown ingots. It is shown that it is possible to grow crystals without contact with ampoule wall which produces the single crystals with absence of striations and dislocation density. This is possible due to the appropriate gap developed in between the solidifying melt and the wall of the ampoule. These ingots growth reveal the high quality bulk single crystals and mobility (GaInSb = 8.1x103 cm2/Vsec at 300K) for typical ingots. The composition X=0.5 reveals the conversion of carriers from n-type to p-type along c-axis. In VDS, we experienced the detached solidification is possible and it is reproducible, reliable and improvement in crystallography and crystal quality.

2:45 PM B3-S3.3
Configuration Control of Quantum Dot Molecules by Droplet Epitaxy. (#1453) Kimberly A Sablon, J H Lee, Zh Wang, J Shultz, G J Salamo; Institute of Nanoscale Science and Engineering, University of Arkansas, USA.

Despite the achievements in fabricating self-assembled quantum dots (QDs) over the last decade and their potentials in optoelectronic device applications, quantum computing and quantum communication, the ability to precisely order them has been challenging. In our previous report [1], we demonstrated the fabrication of several distinctive configurations of InGaAs QDMs from two QDs per GaAs mound (bi-QDMs) to six QDs on each GaAs island (hexa-QDMs). The greatest challenge was ′configuration control′. Here [2], we specifically demonstrate that by changing the substrate temperature at which Ga droplets form and varying the InAs deposition, we are able to control the configuration of quantum dots (QDs) per GaAs mound. The size of the Ga droplets increases with increasing substrate temperature and resulting configurations show a very strong correlation with the size of initial GaAs islands. In distinction from previous reports, we attained two structures, quad-molecules and quantum rod pairs. Quad-molecules are elongated along the [011] crystallographic direction due to strain-driven processes and formed directly at the edges of the GaAs mounds. On the other hand, quantum rod pairs (QRPs) formed along the [01-1] direction due to higher anisotropic diffusion. [1]. J.H.Lee, Zh.M.Wang, N.W. Strom, Yu. I. Mazur, and G. J. Salamo, Appl.Phys. Lett 89, 202101 (2006) [2]. K. A. Sablon, J.H. Lee, Zh. Wang, J. Shultz and G.J. Salamo, Appl. Phys. Lett 92, 203106 (2008)

3:00 PM B3-S3.4
Composition-Dependent Inter-Atomic Distance Distributions and Bond Angles in Ga_1-xIn_xP Alloys Measured by Extended X-Ray Absorption Fine Structure Spectroscopy. (#598) Claudia Sarah Schnohr¹, Leandro L. Araujo¹, Patrick Kluth¹, David J. Sprouster¹, Garry J. Foran², Mark C. Ridgway¹; ¹Electronic Materials Engineering Department, Research School of Physical Sciences and Engineering, The Australian National University, Australian Capital Territory, Australia ; ²Australian Nuclear Science and Technology Organisation, Australia.

Ternary alloys have long been studied due to the potential of tuning their properties with composition x between the two endpoint values of the binary compounds. The atomic-scale structure is crucial in determining these properties and one important question is how the mismatch of the two different binary lattice constants is accommodated in the ternary alloy. Despite many studies, systematic data is still lacking for some of the technologically important systems, particularly in regard to atomic neighbours beyond the first shell. In this work, we present the composition-dependent inter-atomic distance distributions of the first three shells around Ga and In atoms in Ga1-xInxP measured by extended X-ray absorption fine structure (EXAFS) spectroscopy [1]. Ga1-xInxP/AlAs/GaAs heterostructures with compositions x = 0.34, x = 0.50 and x = 0.70 were grown by metal organic chemical vapour deposition and processed with selective chemical etching. GaP and InP samples were also prepared for comparison. The EXAFS of the Ga and In K edges was measured in transmission mode at a temperature of &sim 20 K. Measurements were performed at the Australian National Beamline Facility at the Photon Factory in Japan. The first nearest neighbour (NN) distance distribution is clearly bimodal. The bond lengths for Ga-P and In-P pairs depend linearly on the composition x of the alloy, however, they remain close to the values of the binary compounds even in the dilute limit. This behaviour is in stark contrast to that of the lattice constant which changes linearly with x from one binary value to the other (Vegard's Law). The widths of the Ga-P and In-P distance distributions are similar to those of the binary compounds over the whole compositional range. This picture is similar to the findings in other ternary alloys and confirms the result reported in the sole experiment on Ga1-xInxP we are aware of [1]. The second NN distance distribution shows three peaks corresponding to the three different cation-cation pairs but the mean distances are much closer to the virtual crystal approximation (VCA) than for the first shell, similar to findings for Ga1-xInxAs [2]. The widths of the distance distributions for all pairs are significantly increased compared to the two binaries. The third shell mean distance is well approximated by the VCA, due to the averaging over various local atomic arrangements, though the distribution is again significantly broadened. The tetrahedral bond angles around a central P atom can be calculated for the three different cation-cation pairs. They vary from each other and show a significant change with composition x. This clearly demonstrates that the lattice mismatch is accommodated in the ternary structure primarily by bond angle relaxation. [1] C.S. Schnohr, L.L. Araujo, P.Kluth, D.J. Sprouster, G.J. Foran, M.C. Ridgway, to be submitted. [2] J.B. Boyce, J.C. Mikkelsen Jr., Ternary and Multinary Compounds, Mat. Res. Soc., 359 (1987). [3] J.C. Mikkelsen Jr., J.B. Boyce, Phys. Rev. B 28, 7130 (1983).

AFTERNOON BREAK 3:30 PM - 4:00 PM

4:00 PM *B3-S4.1 (invited)
Effects of Surface Passivation on AlGaN/GaN High-Electron-Mobility Transistors. (#1425) S. Arulkumaran, MMIC Design Center, Temasek Laboratories@NTU, Nanyang Technological University, Singapore.

AlGaN/GaN High-Electron-Mobility Transistors (HEMTs) with 1.5 μm, 0.8 μm and 0.3 μm gate-length were successfully fabricated on sapphire and high-resistivity (HR) silicon substrates. The cutoff frequency (f_T) values of 22 GHz and maximum oscillation frequency (f_max) values of, 40 GHz were achieved for 0.3 μm gate-length HEMTs, respectively. Surface passivation effects on AlGaN/GaN HEMTs were studied using Si₃N₄ dielectric layer grown by plasma enhanced chemical vapor deposition (PECVD). The fabricated device direct (DC) current-voltage (I_DS-V_DS) characteristics, pulsed I_DS-V_DS characteristics, microwave small-signal, microwave noise, and large-signal characteristics were studied before and after passivation studies. An increase of drain current (I_D) density (503 mA/mm to 611 mA/mm) and the extrinsic transconductance (206 mS/mm to 228 mS/mm) was observed for the devices with full Si₃N₄ passivation. Correspondingly, the f_T (35 GHz) and f_max (60 GHz) values were also increased after device passivation. An improvement in device output power (P_out) and small signal noise characteristics were also observed after surface passivation. The minimum noise figure (NF_min) and associated gain (G_a) of passivated device became less dependent on frequency, gate and drain bias. At 10GHz, the NF_min decreased by 25% (0.5 dB) and G_a increased by 10% (1.0dB) at V_d=12V and I_d=50mA/mm. The surface passivation effectively suppressed the drain current collapse more than 80%. A new evaluation technique has been implemented for the evaluation of drain current collapse related traps from AlGaN/GaN HEMTs. Temperature dependant device characteristics will also be discussed.

4:30 PM B3-S4.2
2D Patterned GaN_xAs_1-x Quantum Structures using Energetic Beams. (#711) Taeseok Kim¹, Venkatesh Narayanamurti¹, Michael J. Aziz¹, Kirsten Alberi², Oscar D. Dubon²; ¹Harvard School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, USA ; ²Univ. Calif. Berkeley and Lawrence Berkeley Nat. Lab., USA.

We will present measurements on two dimensionally patterned GaN_xAs_1-x nanostructures fabricated in a GaAs matrix using nitrogen ion implantation followed by pulsed laser melting (PLM) and rapid thermal annealing. The patterned GaN_xAs_1-x regions are investigated by ballistic electron emission microscopy (BEEM), a three terminal scanning tunneling microscopy technique that can image both the surface topography and the local hot electron transport. We identify conditions under which ion implantation through a lithographically patterned mask and subsequent transient thermal processing create locally confined GaN_xAs_1-x dots. By analyzing BEEM images of the dots, we observe the decrease in conduction band edge with increasing nitrogen concentration. BEEM results on patterned dots are compared with a variety of measurements on unpatterned alloy films: BEEM on unpatterned alloy films made by PLM and by MBE, and photomodulated reflectance measurements on films made by PLM. All measurements display the giant bandgap bowing effect.

4:45 PM B3-S4.3
Annealing Effect of the Co Ion-Implanted ZnO Epitaxial Thin Film. (#978) Yen-Fa Liao, Tzu-Wen Huang, Kuan-Li Yu, Chih-Hao Lee; Department of Engineering and System Science, National Tsing Hua University, Hsinchu, Taiwan.

The Co doped ZnO material has more potential applications such as spin LED or solar cell. In this study, we report magnetic property and structure of the Co doped ZnO using ion-implanted technique. The ZnO epitaxial thin film growth sapphire substrate (0001) using ion beam sputter was implanted with Co ions with a nominal dose of 1.0 x 1017 cm-2 at 100 keV ion energy in order to produce a diluted magnetic semiconductor (DMS). After implantation the Co:ZnO thin film was subject to rapid thermal annealing at 600, 700 and 800 degrees C for 30 min respectively. The crystal structure observed by the X-ray diffraction reveals that the well-order on as-made ZnO thin film. The structure of the ZnO thin film was created more defects after Co implanted. The magnetic property of the Co:ZnO show that room temperature ferromagnetism was measured by superconducting quantum interference device (SQUID). The electronic structure of the Co:ZnO was measured by X-ray absorption spectroscopy. The unoccupied state near the Zn L-edge might indicate an impurity band was formed. The impurity band might indicate not only magnetic origin but also improved efficacy of photon-absorb. The photoluminescence measurement shows that a blue shift at the band gap of the Co:ZnO was found when the annealing temperature increased. Our measurements suggest that for a Co concentration in the range of 3-5%, it is possible to prepare a good room temperature DMS after annealing process.

5:00 PM B3-S4.4
Low Temperature III-V Wafer Bonding with Electrically Conductive Interface Facilitated by Dry Surface Passivation Method. (#1153) Michael James Jackson, Mark S Goorsky; Department of Materials Science and Engineering, University of California, Los Angeles, USA.

Direct bonding between III-V materials is often impeded by the presence of unstable oxides and unfavorable electrical properties. To overcome this problem, elevated annealing temperatures (>600 ° C) and large compressive forces are often required to fuse the materials together; such harsh processing conditions can degrade device performance through the diffusion of dopants and residual thermal strain. While the unfavorable III-V oxide layers could be avoided by processing and bonding under ultra-high vacuum conditions, few processes would find that economical. A bonding method that facilitates high mechanical strength, high electrical conductivity, and optical transparency at temperatures compatible with III-V processing is highly desirable for the fabrication of heterogeneous devices such as solar cells. This study investigates the possibility that improved interfacial properties could be attained by treating the III-V surface to hinder oxide formation and un-pin the Fermi level to facilitate an ohmic connection across the bonded interface. A method of III-V surface passivation that uses sulfur vapor and ultraviolet illumination under high vacuum is modified to produce hydrophobic smooth surfaces suitable for bonding. After the sulfur surface treatment and upon contact at room temperature, bonded pairs of GaAs/GaAs, InP/InP, and GaAs/InP exhibit large area bonding without void formation even after annealing at 300-450 ° C. Large compressive forces are not required during the annealing. Crack-opening method tests indicate that bulk fracture strength is achieved in GaAs/GaAs bonding, for example, below 400 ° C. Similar results are achieved with the other combinations. Cross section transmission electron microscopy imaging of the 400 ° C annealed GaAs/GaAs sample shows a continuous interfacial layer of 3-5nm, which is about half as thick as the amorphous layer reported in literature for similar bonding conditions not containing the sulfur passivation process. Current-voltage measurements across the bonding interfaces indicate the bonding method achieves significantly higher conductivity at lower annealing temperatures than reported in literature.

5:15 PM B3-S4.5
Anomalous Transport in Ferromagnetic GaAs/InGaAs/GaAs Quantum Well Delta-Doped with Mn and C. (#1237) Vladimir Kulbachinskii¹, Ljudmila Shchurova², Nicolay Kuznetsov¹; ¹Low Temperature Physics Department, Physics Faculty, Moscow State University, Russian Federation ; ²Physical Institute of RAS, Russian Federation.

Mn-doped GaAs is an attractive diluted magnetic semiconductor for a new spin-based electronics. The Curie temperature (Tc) in Ga1-xMnxAs can be raised by increasing the hole concentration as well as Mn concentration. In the present study we investigated the influence of Mn delta-doping on magnetic and galvanomagnetic properties of GaAs structures with GaAs/InxGa1-xAs/GaAs quantum well. All samples were prepared with the combined method of MOC-hydride epitaxy and laser deposition of Mn. Samples were grown on GaAs (100) substrate and contain carbon delta-layer (to provide enhanced p-type conductivity in the quantum well) and laser-deposited Mn layer (with different Mn content) separated by GaAs spacers with width d=3 nm. For measurements of the magnetization in the temperature interval 4.2-400K in magnetic fields up to 7 T, a SQUID magnetometer was used. The ferromagnetic phase up to 400 K was detected. Different magnetic phases have been found in the samples, one with Tc about 70 K, others with Tc above room temperature (clusters of MnAs and Ga1-xMnx). The first value of Tc is very typical for hole mediated ferromagnetism in Ga1-xMnxAs solid solutions. Hall effect have been measured in the temperature range 4.2-300 K. The anomalous Hall effect is visible up to 195 K and shows influence of ferromagnetism on galvanomagnetic properties of holes. Temperature dependence of resistance in the temperature interval 4.2 - 300 K have been measured. All samples had p-type conductivity and high mobility of holes. In the temperature range between 50 and 110K at zero magnetic field a kink in the temperature dependence of sheet resistance is visible. At higher temperatures the resistance increases with temperature. Negative magnetoresistance is observed in a temperature interval 4.2 -35 K in magnetic field perpendicular to the sample plane and is the most pronounced at the temperatures lower then 20 K. The magnetoresistance changes from colossal negative to enhanced positive with increasing temperature near 35 K. The calculations of temperature dependence of resistance have been carried out. The contributions of various hole scattering mechanisms determining the reason for such temperature dependence are analysed. It is shown that at temperatures smaller than 50 K the resistance is defined by Coulomb scattering, and also spin-flip scattering. The quantitative consistency of the calculated and measured temperature dependence of sheet resistance is found. The reasons for occurrence of negative magnetoresistance are explained quantitatively as the reduction of the spin-flip scattering by aligning spins by magnetic field.

9:00 AM *B4-S1.1 (invited)
Thermal Stability of Ordered Arrays of Au Nanoparticles Deposited on Sapphire. (#684) Paul Ziemann, Frank Weigl, Berndt Koslowski; Solid State Physics, Universität Ulm, Germany.

P. Ziemann, F. Weigl, B. Koslowski Institute of Solid State Physics, Ulm University, D-89081 Ulm, Germany Based on a technique, which exploits the selforganization of precursor loaded spherical micells formed from diblock-copolymers dissolved in an apolar solvent like toluene, arrays of Au nanoparticles were prepared on top of (1120)-oriented Sapphire substrates. For this end, the primarily obtained monolayer of micelles has to be exposed to an optimized plasma process. This micellar method allows controlling the particle size between 1 nm and 12 nm as well as the interparticle distance between 20 nm and 120 nm. Such arrays exhibit narrow Gaussian size distributions and a high degree of hexagonal order [1]. In order to test whether Au nanoparticles with diameters ranging between 1 nm and 5 nm show size dependent vapor pressures as expected from the Kelvin-equation predicting a significant enhancement for smaller particles, thermal desorption spectroscopy (TDS) was performed within the temperature range between 200?C and 1200?C applying linear temperature ramps. In this way, by comparing to bulk Au reference systems, the temperature dependent vapor pressure p(T) of Au nanoparticle arrays could be determined. As the main result, it was found that p(T) of Au particles on Sapphire behave opposite to what is expected from the Kelvin-equation: Smaller particles (< 2.5 nm) exhibit TDS spectra leading to a sublimation energy significantly above the Au bulk value when analyzed according to Polanyi-Wigner. Larger particles, analyzed in the same way, deliver two values for the sublimation energy: One identically enhanced as for small particles and a second one in accordance with the Au bulk value. The volume fraction related to those two values is a monotonic function of the particle size. The data will be discussed in terms of a particle-substrate interaction. We would like to thank H.-G. Boyen for experimental help and useful discussion during the early stage of this study and to Landesstiftung Baden-W?rttemberg "Functional Nanostructures" as well as to Deutsche Forschungsgemeinschaft, SFB 569 for financial support. [1] G. K?stle et al., Adv. Funct. Mater. 13, 853 (2003).

9:30 AM B4-S1.2
Electron Beam Doping in Semiconductors at Room Temperature by Recombination-Induced Defect Reaction. (#948) Takao Wada¹, Hiroshi Fujimoto²; ¹Nagoya Institute of Technology, Japan ; ²Daido Institute of Technology, Japan.

The mechanism of electron beam doping (EBD) has been qualitatively explained using the theory of multiphonon emission of recombination [1]. A semiconductor surface was covered by an overlayer sheet of impurities (neat piles of semiconductor) and the overlayer surface was irradiated with high-energy electrons at 750 keV or 7 MeV, which were operated with a pulse at room temperature. Evidence showing that EBD is not a thermal process has been presented in our previous paper [2]. In the case of a Si substrate overlain with a Ge sheet (t ~0.5 mm), the backscattering spectra by 1.4 MeV He⁺ ions under random conditions were indicated for specimens irradiated at 20, 40 and 60?C in a circulating water bath with a total fluence of 5.1x10¹⁷ e cm^-2 at 7 MeV from an electron linear accelerator. The number of peaks for Ge in Si increases with increasing irradiation temperature [2]. (1) Interstitials of displaced atoms in the overlayer, which were introduced by irradiation, migrated to the surface or the interface of the semiconductor. These strongly diffused atoms at the surface have a very large surface diffusivity in the order of 10^-3cm²s^-1 and also had a volume diffusivity in the order of 10^-17 cm²s^-1. (2) Three-layer structures Si (layer 3)/Ge (layer 2)/ Si (layer 1) of samples were largely irradiated with a total fluence of 7x10¹⁸ e cm^-2 at 7 MeV from an electron linear accelerator. During irradiation, samples were kept in a vacuum of 10^-5 Pa and at about 50 ?C, as shown in our previous paper [2]. From the Auger electron spectroscopy (AES) energy spectra obtained from a front surface of Si (layer 1), the signal intensity of Ge LMM was nearly equal to that of Si KLL [2]. This means that a number of Ge atoms are adsorbed at the Si surface. (3) Spicer et al have proposed a detailed and unified model for Schottky barrier pinning [3]. Their general approach has been to design experiments in which the interaction between the adatoms and semiconductor can be followed at an atomic scale, particularly in the early stages of Fermi-level pinning, i.e., at very low (small fraction of monolayer) coverage [3]. The pinning positions for GaAs fall in a distinct and separate part of the band gap: GaAs near mid-gap. (4) The electron irradiation also produces high concentrations n of electron-hole pairs (EHPs). In the steady state during irradiation, n >> 10²¹ cm^-3 for GaAs, and 10²⁰ cm^-3 for Si. (5) Electron effects can be biased against defect reactions towards new or different reaction products. The large vibration energy will propagate away from the center (deep defects) in the form of lattice phonons. Impurities of adatoms near or at the interface may diffuse via a substitutional-interstitial interchange mechanism. As the semiconductor substrate of layer 1 in GaAs/Zn//Zn/GaAs is not irradiated by 750 keV electrons, vibrational energy sources of atom migrations, due to deep level recombination at the interface may be introduced. Thus, finally, the superdiffusion in semiconductors is given by the kick-out mechanism A_i + e -- > A_i^- + multiphonon emission A_i^- + multiphonon emission --- > A_s + I_i For diffusion of kick-out mechanism in EBD, supersaturation of self-interstitials I_i would result in a decrease in substitutional impurities A_s. The EBD process offers many advantages over alternative doping techniques, because it allows doping even in undamaged regions and at room temperature. [1] C. H. Henry and D. V. Lang, Phys. Rev. B Vol. 15, No.2 (1977) 989 [2] T. Wada and K. Yasuda, Phys. Rev. B 53 (1996) 4770 [3] W. E. Spicer, P. W. Chye, P. R. Skeath, C. Y. Su and I. Lindau, J. Vac. Sci. Technol. 16 (5) (1979) 1422

9:45 AM B4-S1.3
Enhanced Ultra-Violet Photoresponse of Nanostructured Zinc Oxide (ZnO) Thin Film Irradiated with Pulsed Laser. (#1432) Vinay Gupta, Rashmi Menon, K Sreenivas; Electronic Materials and Devices Laboratory, Department of Physics and Astrophysics, University of Delhi, India.

Ultra-Voilet (UV) photodetector is fabricated by rf magnetron sputtered ZnO thin films of different thickness (50 to 400 nm). The average grain size of the ultrathin as-grown ZnO film is between 15-20 nm. The as-grown ZnO films are irradiated by pulsed Nd:YAG laser corresponding to fundamental wavelength (λ=1064nm) and forth harmonics (λ = 266 nm) to enhance the photoresponse characteristics. The photoresponse, (I_on/I_off) of as-grown ZnO film of thickness 100 nm is found to be maximum (3.8 x 10²) with response time of 90 ms for UV intensity of 140 μW/cm² ( λ = 365 nm) in comparison to other film thickness. The laser irradiated photodetector demonstrates increase in photoresponse (3.6 x 10⁴) with fast response speed of 30 ms to UV illumination in air. The photoresponse of both as-grown and irradiated samples are remain same in both air and vacuum, indicating the bulk related photoconductivity. With the increase in film thickness, the photoresponse of irridiated sample decreases. The laser irradiation increases the stress in the ZnO thin film, and the enhanced photo response is attributed to the change in surface defects in ZnO films with laser irradiation.

MORNING BREAK 10:30 AM - 11:00 AM

11:00 AM *B4-S2.1 (invited)
Recent Progress in Mid-IR Interband Cascade Lasers. (#1472) Kamjou Mansour¹, Rui Q Yang²; ¹Jet Propulsion Laboratory, USA ; ²University of Oklahoma, USA.

We report our recent efforts in the development of mid-IR Interband cascade (IC) lasers, which include single mode distributed feedback (DFB) IC lasers and multi-wavelength IC lasers. The single-mode DFB IC lasers can be operated in cw mode at thermoelectrically cooled temperatures (>260K) with tunable range of several wave-numbers to cover trace gas absorption lines. Multi-wavelength IC lasers have been demonstrated with simultaneous multi-color emissions widely spaced in 3 to 5 micron wavelength range. Also, latest results on CW operation of IC lasers at higher temperatures will be updated.

11:30 AM *B4-S2.2 (invited)
A Simple Quasiclassical Treatment of Bias-Dependent Carrier Capture in Quantum Wells. (#658) G. S. Cargill III, Department of Materials Science and Engineering, Lehigh University, Bethlehem, Pennsylvania, USA.

Capture of carriers in semiconductor quantum wells (QWs) plays an important role in quantum well-based light emitting diodes (LEDs), laser diodes and photodetectors, and in studies of QW structures and devices by photoluminescence (PL) and cathodoluminescence (CL). Carrier injection by forward bias of quantum well LEDs and LDs introduces electrons and holes from larger bandgap cladding layers into single or multiple QWs. In quantum well infrared photodetectors (QWIPs) photoexcited carriers are captured in QWs under reverse bias conditions. In PL and CL studies of QW structures and devices, carriers excited in cladding layers diffuse or drift to QWs under different bias conditions, and captured carriers produced QW luminescence. To better understand bias-dependent CL experiments on II-VI QW-LEDs, a simple, quasiclassical treatment of bias-dependent carrier capture has been developed. Capture probabilities for electrons, holes and excitons have been considered. The assumptions and results of this treatment will be discussed. Comparisons will be made with experimental results and with other models for QW carrier capture.

12:00 PM B4-S2.3
Nearly Surface-Free Confinement of Excitons in Single GaAs/AlGaAs Core-Shell Nanowires. (#348) M A Fickenscher¹, S Perera¹, T B Hoang¹, L M Smith¹, H E Jackson¹, J M Yarrison-Rice², Hannah Jane Joyce³, Qiang Gao³, H. Hoe Tan³, Chennupati Jagadish³, Yong Kim⁴, X Zhang⁵, J Zou⁵; ¹Department of Physics, University of Cincinnati, Cincinnati, Ohio, USA ; ²Miami University, Oxford, Ohio, USA ; ³The Australian National University, Australian Capital Territory, Australia ; ⁴Dong-A University, Busan, Republic of Korea ; ⁵The University of Queensland, Brisbane, Australia.

Semiconductor nanowire (NW) heterostructures are becoming important and unique building blocks for electronic and optoelectronic devices. Because of the large surface-to-volume ratio inherent in NWs it is critically important to reduce surface and bulk defects to achieve nearly intrinsic semiconductor behavior. Here we utilize CW and time-resolved photoluminescence (PL) spectroscopy to probe the effect of these defects on exciton recombination in single GaAs/AlGaAs core-shell NWs at low temperatures. The nanowires were prepared by the Au catalyst-assisted vapor-liquid-solid MOCVD process. Photoluminescence emission from single nanowires reveals a prominent exciton peak at 1.515 eV and, depending on growth conditions, a donor acceptor pair response at lower energies along with LO phonon replicas. Exciton recombination lifetimes are extremely sensitive to the presence of surface or interface states, or bulk defects. Because these NWs grow along the [111] direction, twinning defects are a particular problem. Recent growth efforts employing initial NW nucleation at 450C followed by lower temperature (375C) growth of the NW have resulted in twin-free, uniform diameter GaAs nanowires.[1] A 30 nm cladding shell of Al.3Ga.7As was grown on these GaAs cores to passivate their surface, a step necessary to avoid high rates of surface recombination. Here we show that these optimized nanowires can achieve high quantum efficiencies and long exciton recombination lifetimes at 10 K approaching 900 ps. These results are in sharp contrast to earlier work where lifetimes <50 ps were observed [2], and approach the nearly surface-free conditions which have been achieved in high quality GaAs/AlGaAs double heterostructures. Finally, in these nanowires at higher power excitation, we observe state filling and an electron-hole plasma as has recently been reported in high quality single InP nanowires. [3] [1] H. J. Joyce, Q. Gao, H. H. Tan, C. Jagadish, Y. Kim, X. Zhang, Y. N. Guo, and J. Zou, Twin-free uniform epitaxial GaAs nanowires grown by a two-temperature process, Nano Letters 7, 921 (2007).. [2] T.B. Hoang, L.V. Titova, J.M. Yarrison-Rice, H.E. Jackson, L.M. Smith, and C. Jagadish, "Temperature-dependence of photoluminescence from single core-shell GaAs-AlGaAs nanowires," Appl. Phys. Lett. 89, 173126-1-3 (2006). [3] L.V. Titova, T.B. Hoang, J.M. Yarrison-Rice, H.E. Jackson, Y.Kim, H. J. Joyce, Q. Gao, H.H. Tan, C. Jagadish, X. Zhang, J. Zou, and L.M. Smith, "Dynamics of Strongly Degenerate Electron-Hole Plasmas and Excitons in Single InP Nanowires," Nano Letters 7, 3383-3387 (2007). ACKNOWLEDGMENTS We acknowledge support from the National Science Foundation, the Australian Research Council, and the Korean Science and Engineering Foundation.

12:15 PM B4-S2.4
VCSEL Array Based Fluid Flow Measurements Using the Self-Mixing Effect. (#1049) Yah Leng Lim, Russell Kliese, Karl Bertling, Aleksandar D Rakić; School of Information Technology and Electrical Engineering, The University of Queensland, Brisbane, Australia.

Recently, there has been considerable interest in the bio-engineering community in a low cost, non-contact imaging system for measuring velocity distribution of moving particles in fluids. The self-mixing detection technique is a low cost and robust solution for velocity measurements. Conventionally, self-mixing sensors are single point measurement systems. Mechanical scanning is typically employed to facilitate the scanning process when imaging is required. This type of system suffers loss of temporal information between adjacent points and long acquisition time due to slow frame rates. These limitations can be overcome using parallel imaging techniques. In this work, a multi-channel velocity sensor using a 1x12 monolithic VCSEL array for measuring fluid flow is presented to demonstrate the feasibility of a self-mixing based imaging system. The self-mixing signals are obtained directly via the feedback caused variation in laser junction voltage, omitting the need for photo detector. This solution offers significant technological advantage as it removes the need to hybrid integrate a photo detector array with a monolithic VCSEL array and avoids optical crosstalk between adjacent lasers. The system was used to measure the velocity profile of fluid flow resembling to that of blood circulation in peripheral blood vessels. The results obtained show good agreement with the simulated flow profile.

LUNCH 12:30 PM - 2:00 PM

2:00 PM *B4-S3.1 (invited)
Growth Behavior of Epitaxial Semiconductor Nanowire Heterostructures. (#440) Jin Zou¹, Mohanchand Paladugu¹, Yanan Guo¹, Xin Zhang¹, Graeme Auchterlonie¹, Hannah Jane Joyce², Qiang Gao², H. Hoe Tan², Chennupati Jagadish², Yong Kim³; ¹The University of Queensland, Brisbane, Australia ; ²Electronic Materials Engineering Department, Research School of Physical Sciences and Engineering, The Australian National University, Australian Capital Territory, Australia ; ³Dong-A University, Republic of Korea.

Semiconductor nanowires and their associated heterostructures have been paid extensive attention due to their unique physical properties and, in turn, their potential uses in a range of applications from nanoelectronics and optoelectronics to sensors and medical diagnoses. In general, semiconductor nanowires can be synthesized through the vapor-liquid-solid (VLS) mechanism, in which the catalyst particles (in the liquid form) induce nanowire growth. In this study, GaAs-based III-V semiconductor nanowires and their associated heterostructures were epitaxially grown by metal-organic chemical vapor deposition with Au particles (in the size range of 20~90 nm) as catalysts. This presentation summarises our recent achievements in studying GaAs based III-V semiconductor nanowire heterostructures. In the attempt to grow GaSb/GaAs nanowire heterostructures (with 7.8% lattice mismatch), we found that the lattice mismatch is fully relaxed through lateral expansion and no misfit dislocations were found in the GaSb/GaAs interface. Since there are no crystalline defects in the GaSb sections, this study served as the first and the only (so far) observation that the nanowire growth can by fully governed by thermodynamics [1]. To extend this understanding, we also investigated the interface of InAs/GaAs nanowire heterostructures and found that InAs nanowire sections cannot grow axially on top of GaAs nanowire sections [2], but the continuing growth leads to the formation of branched nanowire heterostructures. From these findings, we developed a model to describe our discovery: the interfacial energy of between the Au-catalyst and InAs is higher than that between the Au-catalyst and GaAs, so that Au-catalysts prefer to retain contact with GaAs during the growth of InAs/GaAs or GaAs/InAs nanowire heterostructures [3]. [1] Y. N. Guo, J. Zou, M. Paladugu, H. Wang, Q. Gao, H. H. Tan and C. Jagadish, Appl. Phys. Lett. 89 (2006) 231917. [2] M. Paladugu, J. Zou, Y. N. Guo, G. J. Auchterlonie, H. J. Joyce, Q. Gao, H. H. Tan, C. Jagadish and Y. Kim, Small 3 (2007) 1873. [3] M. Paladugu, J. Zou, G. J. Auchterlonie, Y. N. Guo, Y. Kim, H. J. Joyce, Q. Gao, H. H. Tan and C. Jagadish, Appl. Phys. Lett. 91 (2007) 133115.

2:30 PM B4-S3.2
Investigation on Electro-Optical Switch Using Heterojunction Phototransistors with Double Emitters. (#599) Shao-Yen Chiu, Chung-Hsien Wu, Jung-Hui Tsai, Wen-Shiung Lour; Department of Electrical Engineering, National Taiwan Ocean University, Taiwan.

InGaP/GaAs heterojunction phototransistors with double emitters, named DEPT, have been successfully fabricated as electro-optical switches. Both static and dynamic performances of a DEPT were studied. Static characteristics were obtained when an optical power was incident upon the DEPT with a differential voltage between double emitters. When a clock signal used as an electrical input was applied to a DEPT switch under optical injection, a dynamic response was obtained. In the static case of a DEPT under a 12.5 uW optical power, the emitter-induced gain effect from photocurrent modulation improves collector photocurrent (88 to 129 ?A). Key features associated with a DEPT include the following: (1) double eimtters togeter with the collector work as a three-terminal device, (2) the differential voltage used is only several hunded millivolts, and (3) not only a positive but also a negative voltage can be used to bring about the emitter-induced gain effect. For the DEPT as an electro-optical switch with a 2 V supply voltage, the stable electrical logic swing is 0.41 V for a 1 V clock signal. When a short-period clock signal is applied, a clear electrical logic swing larger than 1.2 V is achieved. The emitter-induced gain effect from both photocurrent modulation and junction-voltage modulation is also introduced to clearly describe DEPT dynamic performance.

2:45 PM B4-S3.3
HgCdTe MWIR Plasma-Type Converted Photodiodes Passivated with MBE CdTe and Low Temperature PECVD SiN. (#561) Ryan James Westerhout, Charles Musca, Jarek Antoszewski, John Dell, Lorenzo Faraone; Microelectronics Research Group, School of Electrical Electronic and Computer Engineering, The University of Western Australia, Australia.

At The University of Western Australia HgCdTe photodiode passivation is a two step process, consisting of a 100nm layer of Molecular Beam Epitaxy CdTe and a thermally evaporated 200nm layer of ZnS. In these devices, the ZnS is also used as an insulator for a gate electrode to control the dark current characteristics of the p-n junction. When measuring the 1/f noise characteristics of these diodes, the gates are subjected to considerable voltage stress, with voltages from 5-10V for several hours. During this time the insulating properties of the ZnS degrade, resulting in the diodes no longer being controlled by the gate electrode. In addition to this problem ZnS is hygroscopic and further degradation of the insulation properties occur if the devices are left in atmosphere. An alternative insulator to ZnS needs to be found. It is proposed that SiN can replace ZnS as the insulator for HgCdTe photodiodes. SiN has been shown to be more moisture resistant than ZnS, as well having a high dielectric field strength, 5x10 6V/cm field breakdown limit, a high resistivity (1x10 16&Omega cm), and being an effective barrier to mobile ions such as Na+. PECVD SiN can be deposited at lower temperatures than other chemical vapor deposition techniques such as low pressure chemical vapor deposition. This low temperature is critical for HgCdTe processing. With this system we are able to control the properties of the SiN such as stress, density, deposition rate and thickness. In contrast, the evaporated ZnS must be deposited at a rate of 0.02nm/s to achieve the required stress and density for passivation. The maximum thickness of the ZnS film is limited to around 200nm, as thicker films tend to crack. To determine a suitable passivation and insulation layer for HgCdTe photodiodes, the properties of various low temperature PECVD SiN films were investigated. Metal-insulator-metal (MIM) capacitors were fabricated on silicon to determine a suitable PECVD SiN film for insulation of HgCdTe diodes. It was found that at a PECVD process temperature of 125° C, high power of 200W, and low process pressure of 300mTorr films gave the best film characteristics. These films were stable in atmosphere, as shown by FTIR measurements, which also shows oxidation of low power, high process pressure films. HgCdTe photodiodes were fabricated with PECVD SiN films with 200W power, 300mTorr pressure, 5:45:100 (SiH4:NH3:N2) gas ratio. Non-gated diodes had R0A values of 8.14x105&Omega cm2 and 6.56 x105&Omega cm2 for 300&mu m and 410&mu m diodes respectively. Gated diode measurements indicated that R0A values of 3.08.14x106&Omega cm2 are achievable with fine-tuning of the SiN charge.

3:00 PM B4-S3.4
Sidewall Effects of MBE Grown CdTe for MWIR HgCdTe Photoconductors. (#1022) Jing Zhang, Ryan James Westerhout, Gordon K. O. Tsen, John M. Dell, Lorenzo Faraone; Microelectronics Research Group, School of Electrical Electronic and Computer Engineering, The University of Western Australia, Australia.

The semiconductor-passivating layer interfaces, as well as the dielectric properties of the passivating layers, play important and very often dominant roles in determining HgCdTe device performance. In this work, photoconductors and MIS capacitors were fabricated on Hg1-xCdxTe (x~0.3) material using Molecular Beam Epitaxy (MBE) deposited CdTe as passivation. Measurements of responsivity of photoconductor devices with and without sidewall passivated by CdTe were made, as well as conductance-voltage characteristics of MIS capacitors using CdTe between HgCdTe and metal contacts. SEM micrographs and X-Ray diffraction spectra were also included in order to investigating CdTe film used for HgCdTe IR device passivation.

3:15 PM B4-S3.5
An empirical potential approach to the formation of InAs stacking-fault tetrahedron in InAs/GaAs(111). (#605) Tomonori Ito¹, Hidenori Joe¹, Toru Akiyama¹, Kohji Nakamura¹, Kiyoshi Kanisawa²; ¹Mie University, Tsu, Japan ; ²NTT Basic Research Laboratories, Japan.

Low-dimensional semiconductor nanostructures have received considerable attention from the scientific and engineering communities because of their small size and large surface to volume ratio. Thus they can be promising candidates for realizing nanoscale devices. Among them, the stacking-fault tetrahedron (SFT) has received a lot of attention due to the possibility of a natural quantum-dot system for electrons. The SFT with nano- to micro-meter size is formed in InAs thin films molecular beam epitaxially grown on GaAs(111) substrate and is surrounded by the (111)A surface and three triangular {111}-stacking fault planes consisting of wurtzite-like stacking layers giving rise to a scattering potential for electrons. Despite the importance of the SFT, there have been very few studies for its structural stability from theoretical viewpoints. This is because of the difficulty in estimating a small energy difference between normal stacking and stacking-fault layers. In our previous studies, a simple systematization of structural trend in the bulk form has been carried out by description of energy difference between wurtzite and zinc blende structures. This description based on electrostatic energy developed a new empirical potential, which has been successfully applied to investigate the structural stability for the bulk phase, thin films, dislocation core structures, and nanowires. In this study, we extend our approach to the InAs-SFT formation on GaAs(111). To this end, the structural stability of the InAs-SFT is discussed in terms of strain relaxation by comparing the calculated cohesive energies for various InAs/GaAs(111) systems such as coherently grown InAs, relaxed InAs with misfit dislocations (MDs), InAs with threading dislocations (TDs), and InAs with SFT. The calculated results reveal that InAs with SFT is more stable than coherently grown InAs beyond the film thickness of 21 monolayers (MLs). The critical film thickness of 21 MLs is comparable with that of 8 MLs for the MDs generation. Furthermore, SFT formation in InAs is more favorable than TDs formation in InAs below the film thickness of ~60 MLs. These calculated results are qualitatively consistent with experimental results and can be systematically interpreted by considering individual energy contribution in the SFT-apex, -ridge, and -face regions. We found that the energy profit due to strain relaxation in the SFT-face depending on the square of the film thickness particularly plays a crucial role for stabilizing the SFT in InAs thin films grown on GaAs(111). Consequently, these results obtained in this study suggest that the SFT appears in InAs thin film layers instead of MDs and TDs resulting from lowering the strain energy accumulated in InAs thin film layers on GaAs(111).

AFTERNOON BREAK 3:30 PM - 4:00 PM

4:00 PM *B4-S4.1 (invited)
Unraveling the free electron behavior in InN. (#1431) Vanya Darakchieva, Department of Physics, Chemistry and Biology, Linköping Univeristy, Sweden.

Precise measurement of the optical Hall effect in InN using magneto-optical generalized ellipsometry at IR and THz wavelengths allows decoupling of the surface accumulation and bulk electron densities in InN films by non-contact optical means and further to precisely measure the effective mass and mobilities for polarizations parallel and perpendicular to the optical axis. Studies of wurtzite and zinc-blende InN films with different thicknesses, free-electron densities, surface orientations and polarities enable an intricate picture of InN free carrier properties to emerge. Electron accumulation is found to occur at polar, semi-polar and non-polar surfaces of wurtzite and zinc-blende InN films and the surface charge shows distinct dependence on the bulk free-electron density. Striking findings on the scaling factor of the bulk electron density with film thickness points to the existence of an additional thickness-dependent doping mechanism, different from currently accepted picture and suggest that the complexity of the surface chemistry might have been underestimated in the existing models.

4:30 PM B4-S4.2
Characterisation of Nitrogen-Related Defects in Compound Semiconductors by Near-Edge X-Ray Absorption Fine Structure. (#124) Mladen Petravic, Department of Physics, University of Rijeka, Croatia.

We have used synchrotron-based near-edge x-ray absorption fine structure (NEXAFS) spectroscopy to study the electronic structure of nitrogen-related defects in several compound semiconductors, such as GaN, InN, GaSbN or InSbN. Several defect levels within the band gap or the conduction band were clearly resolved in NEXAFS spectra around the nitrogen K-edge. We attribute these levels to interstitial or antisite nitrogen, in good agreement with some theoretical calculations. A sharp resonance observed in all samples under consideration above the conduction band minimum was attributed to molecular nitrogen, in full agreement with the vibrational fine structure of the N 1s &rarr 1&pi* resonance in molecular nutrogen. This fine structure exhibits substantially larger lifetime linewidth &Gamma than in isolated nitrogen molecules. A clear correlation between &Gamma ?and the lattice constant of the host matrix has been found, indicating that the broadening of vibrational levels is governed by a finite probability of the electron to escape from the &pi* orbital into the matrix.

4:45 PM B4-S4.3
Amorphisation of Compound Semiconductors - A New Insight into Ternary Compounds. (#492) Zohair S Hussain¹, Claudia S Schnohr¹, Garry J. Foran², Mark C Ridgway¹; ¹Electronic Materials Engineering Department, Research School of Physical Sciences and Engineering, The Australian National University, Australian Capital Territory, Australia ; ²Australian Nuclear Science and Technology Organisation, Australia.

Amorphous semiconductors are widely used in the optoelectronic industry for various applications such as fibre optical amplifiers and solar cells. With amorphous semiconductor usage growing, it is important to understand the mechanism for the crystalline to amorphous phase transformation in these materials so that properties can be better tailored for specific applications. In(sub)xGa(sub)1-xAs and In(sub)xGa(sub)1-xP are two such semiconductors. Recently, ion implanted In(sub)xGa(sub)1-xAs has been shown to have an anomalous amorphisation behaviour: unlike other ternary alloys, such as Al(sub)xGa(sub)1-xAs, it does not exhibit amorphisation kinetics intermediate between the two binary extremes. We attributed this behaviour to the pre-existing strain present at the microscopic level due to a bimodal bond length distribution and bond angle distortions in the ternary alloy. This model should also be applicable to In(sub)xGa(sub)1-xP. In this study we report on preliminary investigations into the amorphisation behaviour of ion implanted In(sub)xGa(sub)1-xP, using Rutherford backscattering spectroscopy in the channelling configuration (RBS-C) and extended x-ray absorption fine structure spectroscopy (EXAFS). Results are compared with other binary and ternary alloys. Amorphisation kinetics studied with RBS-C were fit using the defect interaction and amorphisation model of Hecking et al. We find that In(sub)xGa(sub)1-xP amorphisation behaviour is similar to that of In(sub)xGa(sub)1-xAs. In conclusion, we show that In(sub)xGa(sub)1-xP also has an anomalous amorphisation behaviour which is attributed to the pre-existing microscopic strain due to the presence of bond angle distortions.

B4-S5.1
First-Principles Study of Electronic Structure and Ground-State Propterties of Alkali-Metal Selenides and Tellurides (M2A) [M: Li, Na, K; A: Se, Te]. (#22) Rajagopal Dashinamoorthy Eithiraj, Department of Physics, Anna University, Chennai, India.

First-principles calculations have been performed to investigate the electronic structure and ground-state properties of alkali-metal Selenides (M2Se) and Tellurides (M2Te) [M: Li, Na, K] using the Tight-Binding Linear Muffin-Tin Orbital (TB-LMTO) method. The exchange correlation energy is described within the local density approximation (LDA) using the von-Barth and Hedin parameterization scheme. At ambient conditions these compounds are found to crystallize in the face centre cubic antifluorite (anti-CaF2-type) structure. Ground state properties such as total energy, equilibrium lattice parameter and bulk modulus are calculated for these compounds. The calculated equilibrium lattice parameter is in agreement with experimental result. From the electronic structure calculations, we find that Li2Se, Li2Te, K2Se and K2Te are indirect bandgap semiconductors, whereas Na2Se and Na2Te are direct bandgap semiconductors. The present results are compared with the earlier results of series of alkali metal sulfides (M2S) and alkali metal oxides (M2O), allowing us to make predictions about the total energy, bulk modulus, valence band width and bandgap behavior of the rest of the alkali chalcogenide crystals (ACC).

B4-S5.2
Approach for Selecting Appropriate Dopant and Doping Method for Metal Oxide Semiconductors. (#28) Mohsen Purahmad, Electrical Engineering Faculty, K.N.Toosi University of Technology, Iran.

Metal oxide semiconductors are widely used in a variety of electrical and optical applications .Among materials that are implemented for these applications, TiO2, SnO2, and ZnO are more attractive than others. These semiconductors have been recognized excellent materials for applications such as: photovoltaic, photo catalytic, optoelectronic, gas sensor and like. It is due to their high sensitivity, non-toxic nature, large band gap and good structural properties. However, in order to improve electrical and optical properties of these materials, different dopants and additives are often used. Depending on the desired application, we should trade off between the electrical properties and wide band gap advantages by choosing an appropriate doping method and dopands. Many researchers have proposed various methods and different dopants in order to dope these materials for different applications. But, there is not any comprehensive report discussing how to choose appropriate dopants and doping method for each specific application. Since in each application one property is dominant, we have studied the electrical and optical properties of TiO2, SnO2, and ZnO, and based on previous literatures, we have proposed a method for selecting the most appropriate dopant and better doping method for each specific application. Also for each selection model, we provided a theoretical reason to support it.

B4-S5.3
Characterization of Enhancement-mode InP N-channel MOSFET with LPD-TiO2 Gate Oxide. (#43) Ming-Kwei Lee, Department of Electrical Engineering, National Sun Yat-sen University, Kaohsiung, Taiwan.

Characterization of Enhancement-mode InP N-channel MOSFET with LPD-TiO2 Gate Oxide Ming-Kwei Lee and Chih-Feng Yen Department of Electrical Engineering, National Sun Yat-sen University, Kaohsiung, 80424, Taiwan, R. O. C. Tel: 886-7-5252000 ext. 4120 Fax: 886-7-5254199 E-mail: mklee@mail.ee.nsysu.edu.tw Abstract Due to the high electron mobility and direct energy band gap compared with Si, much attention has been focused on indium phosphide (InP) high-speed and optoelectronic devices. Compared with metal oxide semiconductor field effect transistor (MOSFET), the main disadvantage of MESFET is the high gate current of Schottky contact under the positive bias of several tenths of a volt, which severely limits the maximum drain current, the noise margin and the flexibility of the circuit design. The gate insulating layer of MOSFET can improve those disadvantages. Titanium dioxide (TiO2) can provide higher lattice match with InP and therefore a lower density of interface states compared with SiO2. In addition, TiO2 is a high dielectric constant (high-k) material (?// =170, ??= 89 for its rutile phase). The transconductance of MOSFET is higher with higher dielectric constant material as the gate oxide. The ammonium sulfide ((NH4)2Sx) treatment could prevent InP from oxidation after cleaning and improve the interface properties. Moreover, the (NH4)2Sx treatment will form the chemically bonded In-S spies on InP surface and assist the crystalline reconstruction of InP surface. For the traditional preparation of oxides, the high temperature process will break In-S bonds on InP surface. The passivation function of the (NH4)2Sx treatment is degraded due to the replacement of S with O and the unstable oxide is formed. Therefore, a low temperature growth process is essential for the growth of high quality amorphous oxide on InP. Liquid phase deposition (LPD) is a low temperature growth process (room temperature is permissible) and has other advantages such as selectivity, large area and simple process. Zn doped P-type (100) InP with carrier concentration of 6 x 1016 cm-3 was used as the substrate in this study. After cleaning, InP substrate was immediately dipped into (NH4)2Sx solution for 40 min at 50oC and then blown dry with nitrogen gas (S-InP). After (NH4)2Sx treatment, InP substrate was thermally annealed at 250oC in a nitrogen atmosphere for 10 min to desorb the excess of weakly bonded sulfide and the InP substrate with (NH4)2Sx treatment is ready for LPD-TiO2 deposition. Without the thermal annealing, the electrical properties of LPD-TiO2 films are poor due to the excess of sulfide near the interface. The aqueous solution of hexafluorotitanic acid (H2TiF6) (6.15 M) saturated with titanium oxide and boric acid (H3BO3, 0.856 M) were used for the LPD-TiO2 deposition at 70oC. The as-grown LPD-TiO2 films on InP without (NH4)2Sx treatment shows a mirror like surface. The growth rate increases with the H3BO3 volume. It is from that more HF neutralization with the H3BO3 concentration drives higher super-saturation of TiO2 in the growth solution. But TiO2 precipitation will be formed in the growth solution with too high H3BO3 concentration. It would degrade the quality of TiO2 films. The deposition temperature is fixed at 75oC and the deposition time is fixed at 40 min. The thickness of LPD-TiO2 films on InP are 30, 60, 160 and 370 nm corresponding to the H3BO3 volume of 2, 4, 8 and 12mL examined by scanning electron microscopy. Basically, the LPD-TiO2 films on InP substrate with or without (NH4)2Sx treatment show an amorphous-like structure examined by X-ray diffraction due to the very low growth temperature. The leakage current of LPD-TiO2 films on InP substrate without (NH4)2Sx treatment as a function of H3BO3 volume showed the leakage current is lower with decreasing the H3BO3 volume and has several orders difference from 2 to 12mL. With decreasing the H3BO3 volume, the interface quality of TiO2/InP is gradually improved due to sufficient in-situ HF etching and the TiO2 film quality is better due to lower growth rate. For the H3BO3 volume fixed at 2mL, the leakage currents are 6.4 x 10-8 and 2.2 x 10-4 A/cm2 at ?0.5 MV/cm. For the leakage current of LPD-TiO2 films on InP substrate with (NH4)2Sx treatment as a function of H3BO3 solution volume, the leakage current increases with the positive bias, and it is higher than that without (NH4)2Sx treatment. It is from the improvement of interface quality by the reconstruction InP surface, and the intrinsic carrier concentration is higher to result in a higher leakage current. Under the negative bias, the leakage current is much lower than that without (NH4)2Sx treatment. It means that higher quality of TiO2 films and interface can be obtained with (NH4)2Sx treatment. Generally, the leakage current decreases with decreasing the H3BO3 volume. But, as the H3BO3 volume decreases to 2mL, the leakage current is higher. It could be from the destruction of InP sulfur reconstruction surface due to too high HF concentration. The optimum H3BO3 volume is 4mL. The leakage currents are 2 x 10-7 and 7 x 10-7 A/cm2 under positive and negative electric fields at 0.5 MV/cm, respectively. For the C-V characteristics of LPD-TiO2 films on InP substrate without (NH4)2Sx treatment as a function of the H3BO3 volume, the increase of accumulation capacitance with the decrease of the H3BO3 volume is partly from the decrease of the film thickness. Due to the improvement of the leakage current after (NH4)2Sx passivation, the accumulation capacitances for all samples are higher than that without (NH4)2Sx treatment. The dielectric constants are 4, 43 and 17.4 corresponding to the H3BO3 volume of 2, 4 and 8mL. Therefore, the especial higher dielectric constant TiO2 film can be obtained. TiO2 films with and without (NH4)2Sx treatment show the negative effective oxide charges, which could be from the F- ions. The negative effective oxide charges decrease with decreasing the H3BO3 volume but increase at the H3BO3 volume of 2mL. The minimum negative effective oxide charges reach - 2 x 1011 C/cm2 for the H3BO3 volume of 4mL due to the best S passivation. The Dit of LPD-TiO2/S-InP with H3BO3 volume 2, 4, 8 and 12mL derived from Terman method are 1.5 x 1012, 8 x 1011, 2.1 x 1012 and 2.8 x 1012 cm-2eV-1 at the energy of 0.78 eV from the edge of valence band. The distribution of interface state density shows a U shape. It indicates that there is no addition impurity level in the energy bandgap. The flatband voltage shifts (?VFB) of hysteresis loops for H3BO3 volume 2, 4, 8 and 12mL are 0.18, 0.13, 0.21 and 0.27 V, respectively, which are consistent with the trend of Dit. For the fabrication of enhancement-mode LPD-TiO2/S-InP NMOSFET, Si ions are implanted with a dose of 5 x 1013 cm-2 at 130 keV to create n+ source and drain. The Si ion activation process is carried out using the rapid thermal annealing (RTA) at 820oC for 20 sec in N2. The contacts of source and drain regions were metallized with In-Zn alloy and then thermally annealed at 400oC in a nitrogen atmosphere for 3 min. The Al layer was thermally evaporated as the gate electrode and defined using the lift-off technology. The DC characteristics of the 4 x 100 ?m2 enhancement mode InP MOSFET shows very low off-current and complete saturation, which indicates the good quality of the LPD-TiO2 (60 nm)/S-InP interface. The normalized maximum gm is 43 mS/mm at VG = 1.3 V for VDS fixed at 1 V. The maximum electron mobility ?FE of 348 cm2/Vos at VDS = 1 V is obtained. It is the first time to fabricate the enhancement InP MOSFET using LPD-TiO2 as the gate oxide. It has high potential in the future development.

B4-S5.4
Carrier Gas Dependence of Quantum Dot Formation by LP-MOCVD. (#48) Zongyou Yin, Jixuan Zhang, Hao Gong; Nanyang Technological University, Singapore.

InAs quantum dots (QDs) formation on InGaAs/InP(100) by low-pressure metal-organic chemical vapor deposition (LP-MOCVD) in pure-hydrogen (P-H2), pure-nitrogen (P-N2) and hydrogen-nitrogen mixed ambient has been studied. The dot's surface coverage and crystal quality are strongly dependent on the carrier gas mode in the reactor. Surface coverage of the dots formed in the mixed or P-H2 ambient reaches almost 100%, much higher than that of ? 40% for the dots formed in P-N2 ambient. This is due to QDs' lateral coupling growth in mixed or P-H2 ambient induced by the larger diffusion length of surface adatoms carried by H2 than carried by N2. The lateral coupling growth with dot's lateral size expansion is also observed in the transmission electron microscope (TEM) images. Such lateral coupling growth induces more grown-in defects in the dots, thus degrading the layer crystal quality. This is confirmed by the thermal annealing on the QDs grown under P-H2 and P-N2: photoluminescence (PL) intensity increases with linewidth narrowing for the dots grown in P-H2 ambient, but PL intensity decreases with linewidth broadening for the dots formed in P-N2 ambient upon the same thermal annealing.

B4-S5.5
Crystal Growth of CZT and its Properties for the Application in X-Ray and Gamma-Ray Detectors. (#106) Wanqi Jie, Tao Wang; School of Materials Science and Engineering, Northwestern Polytechnical University, Xi'an, China.

The paper reports the recent achievement of the research on CZT for the application of X-ray and gamma-ray detectors in Northwestern Polytechnical University. The crystals of both un-doped and In doped were grown with a self-designed Bridgman furnace. The microstructure analyses show that the crystals possess high crystallinity. Through In doping, the electronic properties were greatly improved and as high as 5x10 power 10 Omiga cm resistance was obtained. The detectors produced with our crystal exhibits high resolutions of energy spectra for Thc-ca, 241Am, 137Cs, and 207Bi.

B4-S5.6
Gas-Sensing Properties of Perovskite-Type CdSnO₃ Based Semiconductors. (#146) Xiaohua Jia, Huiqing Fan; School of Materials Science and Engineering, Northwestern Polytechnical University, Xi'an, China.

The CdSnO3 semiconducting complex oxides that can be used as a gas-sensing material for detecting ethanol gas were prepared by a chemical co-precipitation method, of which the synthesis conditions were carefully controlled. After calcinations at 600 ? for 1 h, the n-type semiconductor gas-sensing CdSnO3 was obtained. The phase, particle size and microstructure of CdSnO3 powders were characterized by the X-ray diffraction (XRD), the Brunauer-Emmett-Teller (BET) method with a gas adsorption analyzer and the transmission electron microscopy (TEM). It shows that the CdSnO3 based powders correspond to a small particle size range of 100-130 nm and surface area of 9.2 m2/g. The gas-sensing mechanism was discussed with the X-photoelectron energy spectra (XPS) and the infrared spectra (IR) detections. Moreover, the gas sensitivity, operating temperatures and selectivity of CdSnO3-based sensors with and without different noble metal dopants were also investigated, such as Au, Re, Ru. Au, Re, Ru were incorporated into CdSnO3 by impregnation technique. The gas sensitivity property was measured in detail by using HWC30A. The CdSnO3 is an n-type semiconductor and the sensor response of the doped CdSnO3 sensors was superior to that of the undoped CdSnO3. The 1.0 wt.% Ru doped CdSnO3-based sensors have satisfactory sensitivity and selectivity H2S gas, however, the CdSnO3 sensors had good sensitivity and selectivity to vapor of C2H5OH.

B4-S5.7
Electronic Behavior of Indium-V Semiconductors. (#243) Uma Shankar Sharma¹, U P Verma²; ¹Department of Physics, Rustamji Institute of Technology - BSF, Tekanpur, India ; ²Jiwaji University, Gwalior, India.

Electronic and structural properties of Indium compounds such as InN, InP, InAs and InSb have been performed by ab-initio calculations under zinc-blende phase. The calculations are based on the concept of total energy minimization and values of parameters used in these calculations are finalized after optimization. In this work, we are interested in finding common trends and differences in the electronic structure for these compounds. Results are determined for lattice constant, bulk modulus, pressure derivatives and band structure of indium-V compounds and determined the pressure effect on both direct (?-?) and indirect (?-X) band gaps.

B4-S5.8
Exact Analytical Expression for Quantum Corrections to the Conductivity (Magnetoresistance): Alavi-Rouhani Equation.. (#314) (Seyed) Ali Asghar Alavi, Abdolrashid Tatar; Department of Physics, Sabzevar University of Tarbiat Moalem, Iran, Iran.

We study the quantum corrections to the conductivity (magnetoresistance) for semi-conductors with var- ious structures at low temperatures. We show that the exact analytical expression [1], compared with the existing expression [2], is in better agreement with experimental data on heterostructures and on heavily doped strongly disordered semiconductors. The analytical expression for quantum corrections to conduc- tivity given in [2] has been used by physicists for scores of years. On the other hand from a theoretical point of view we show that our equation is also rich because it establishes a strong relationship between quantum corrections to the conductivity and the quantum symmetry SU_{q}(2). As a result we show that the quantum correction to the conductivity is the trace of the Green function formed by the generator J_{y} of the SU_{q}(2) algebra, so the quantum corrections to the conductivity can be expressed as a sum of an infinite number of Feynman diagrams (exactly in the same way as in quantum field theory). We observe that the quantum corrections to the conductivity increase as the temperature decreases. We also show that the phase breaking time  at low temperatures varies inversely with temperature. [1]. S. A. Alavi, S. Rouhani, Phys. Letts. A 320, 327 (2004) [2]. A. Hikami et. al., Prog. Theor. Phys. 63, 707 (1980)

B4-S5.10
The Thermal Expansion of Mercury Indium Telluride Crystals. (#495) Linghang Wang, Wanqi Jie, Yang Yang; State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, China.

Mercury indium telluride (MIT) crystal is one of the most promising novel materials for room temperature near infrared photovoltaic detectors because of the high quantum efficiency of photoconductivity, high resistance to ionizing radiation and insensitivity to impurities. In this paper, The thermal expansion behaviors of mercury indium telluride crystals, Hg(3-3x)In2xTe3 (x=0.5), based on x-ray diffraction experimental data were studied in the temperature range of 298-573K. The variation of the lattice parameter of the as-grown mercury indium telluride crystals with temperature was determined and the thermal expansion coefficient was deduced to be 6.18x10^-6K^-1. The results of the thermal expansion are best fitted to polynomial expressions. It is found that the lattice parameter decreases quickly with the temperature increasing in the temperature range of 298-330K and then increases continuously up to 573K. The minimum lattice parameter corresponds to a maximum shrinkage of 0.06%.

B4-S5.11
InP/InGaAs pnp Heterostructure-Emitter Bipolar Transistor. (#553) Jung-Hui Tsai¹, Shao-Yen Chiu², Wen-Shiung Lour², Yu-Chi Kang¹, Ning-Xing Su¹; ¹Department of Electronic Engineering, National Kaohsiung Normal University, Kaohsiung, Taiwan ; ²National Taiwan Ocean University, Taiwan.

Over the past years, npn heterojunction bipolar transistors (HBTs) in connection with pnp HBTs were widely used for implementations of low power complementary integrated circuits and push-pull microwave amplifiers. For InP/InGaAs pnp HBTs, though a large conduction band discontinuity of 0.25 eV at InP/InGaAs heterojunction provides good confinement effect for electrons, a relatively large valence band discontinuity of 0.35 eV is still a significant factor to cause large potential spike at emitter-base (E-B) junction and emitter-collector (E-C) offset voltage. This increases the unnecessary power consumption in digital circuit applications. In this article, we first fabricate an InP/InGaAs pnp heterostructure-emitter bipolar transistor (HEBT) with a heavy-doped and thin p+-InGaAs emitter layer at E-B junction by LP-MOCVD system. For the pnp device, the confinement effect for holes is good by the presence of large valence band discontinuity at InP/InGaAs heterojunction. Therefore, high emitter injection efficiency and high current gain are expectable to obtain. The employment of p+-InGaAs emitter layer between the InP confinement and n+-InGaAs base layers introduces the p-n junction as homojunction and could maintain the quality of interface. Thus, the addition of a heavy-doped and thin p-InGaAs emitter could achieve high current gain and low offset voltage even under forward E-B voltage, simultaneously. Transistor performance exhibits a maximum collector current of -3.7 mA and a maximum current gain of 88, respectively. A relatively low offset voltage of only 54 mV is observed at IB = -5 mA. To our knowledge, the offset voltage of the device is the lowest value among of the reported InP/InGaAs pnp HBTs. The ideality factors nc for collector current is nearly equal to unity at low current level. It means that the thermionic-emission and diffusion mechanisms dominate the hole transportation across the E-B heterojunction. Also, a low turn-on voltage of E-B junction about 0.37 V is obtained at the current level of 0.1 mA, attributed to the elimination of the potential spike and the use of the small energy-gap InGaAs base. This can reduce the operation voltage and decrease the power consumption in circuit application. On the other hand, the ideality factor nb for base current is equal to 1.2 at low current level, which means that the addition of a thin p+-InGaAs emitter does not increase base recombination current and degrade the device performance. Furthermore, a high current gain is observed at low current level based on the elimination of potential spike. Thus, the studied device exhibiting high device linearity, i.e., current gain versus IB, is proper for linear and signal amplifier applications.

B4-S5.12
Investigation of Field-Plate Gate on Heterojunction Doped-Channel Field Effect Transistors. (#645) Meng-Kai Hsu¹, Shao-Yen Chiu¹, Chung-Hsien Wu¹, Kang-Ping Liu¹, Jung-Hui Tsai², Wen-Shiung Lour¹; ¹Department of Electrical Engineering, National Taiwan Ocean University, Taiwan ; ²Electrical Engineering, National Kaohsiung Normal University, Taiwan.

Heterojunction doped-channdel field effect transistors (HDCFETs) with field-plate gate (FP-gate) were fabricated and investigated. The arrangement of FP-gate that the gate metal is based across a step undercut between the Schottky barrier and the insulator-like bulk layer is the key configuration and therefore a controllably reduced gate length was simultaneously performed. The 2D semiconductor simulator software was employ to investigate the electric field reducing effect of FP-gate on HDCFET. Comparing the measured results of fabricated devices with FP-gate were identical as well as simulated results that the FP-gate could effectively reduce the electric field under the Schottky metal between the gate to drain side, hence the characteristic improvement were achieved. A HDCFET with a gate-metal length of 0.4 um, a field-plate length of 0.6 um, and an insulator-thickness of 120 nm was successfully fabricated for comparing to that with a traditional 1-um planar gate. Current density (451 mA/mm), transconductance (225 mS/mm), breakdown voltages (VBD(DS)/VBD(GD)=22/-25.5 V), gate-voltage swing (2.24 V), unity current-gain and power-gain frequencies (ft/fmax=17.2/32 GHz) are improved as compared to those of 1-um planar gate device without field plates. At a VDS of 4.0 V a maximum PAE of 36 % with an output power of 13.9 dBm and a power gain of 8.7 dB was obtained. Saturated output power and linear power gain are 316 mW/mm and 13 dB, respectively.

B4-S5.13
Laser Beam Induced Current for Qualitative Evaluation of HgCdTe van der Pauw Sample Uniformity. (#986) Benjamin Alan Park, School of Electrical Electronic and Computer Engineering, The University of Western Australia, Australia.

HgCdTe is a semiconductor that is commonly used to fabricate high-performance infrared detectors. Highly desirable features of this material include the ability to tune the bandgap of this material across the entire infrared spectrum with near-constant lattice parameter, in addition to the direct bandgap and high quantum efficiency. However, it is also a very difficult material to work with, primarily due to the relatively weak bonding of Hg in the crystal lattice, and suffers from yield and uniformity issues. Carrier transport characterization is typically done by measuring the Hall and resistivity properties of a material, from which it is theoretically possible to calculate the concentration and mobility of mobile charged carriers. Such information is particularly useful when evaluating the quality of material and designing devices. In the case of HgCdTe, this characterization is generally very difficult, primarily due to the often unintentional existence of multiple layers and multiple carriers of different signs. The conditioning of the raw Hall and resistivity data with reversed magnetic field polarity and/or reversed current direction must meet strict requirements before it is appropriate to perform further calculations to extract the carrier transport properties. For HgCdTe, the conditioning of the raw Hall and resistivity data is particularly sensitive to the material uniformity. Laser beam induced current (LBIC) is an optically-based characterization tool that can be used to investigate the electrical properties of a material. It involves raster-scanning a low-power focused laser beam across the sample surface, which generates electron-hole pairs in the material. If these photogenerated carriers can diffuse to an electric field, such as that associated with an electrically active defect or junction, they will be swept apart and the induced current can be measured between two remote contacts. LBIC has previously been investigated for applications in material quality screening and as a means to determine the properties of n-on-p junctions. In this work, the conditioning of Hall and resistivity measurements of HgCdTe van der Pauw samples has been correlated with LBIC measurements to investigate the probable causes of "anomalous" trends in the behaviour of these measured voltages with changing magnetic field direction or polarity. It has been found that spatial nonuniformity in the electrical properties of the sample is associated with poorly conditioned Hall and resistivity measurements. In addition, the quantitative carrier transport results from the Hall and resistivity measurements have also been compared to the qualitative features of the LBIC profiles. Increases in the peak LBIC magnitude, and a longer characteristic length of decay away from this peak, can be positively associated with a thicker and/or higher quality n-type layer on underlying p-type material. This is a potentially useful and simpler alternative to the Hall and resistivity measurements for a qualitative indication of the n-on-p layer carrier transport properties.

B4-S5.14
Investigation of the Behavior of the VCSEL Linewidth Enhancement Factor under Optical Feedback using the Self-Mixing Technique. (#1051) A. Ashrif A. Bakar¹, Tom Taimre², Yah Leng Lim¹, Russell Kliese¹, Aleksandar D. Rakić; ¹School of Information Technology and Electrical Engineering, The University of Queensland, Brisbane, Australia ; ²Department of Mathematics, The University of Queensland, Brisbane, Australia.

Operating lasers under optical feedback induces spectral effects, such as improved side mode suppression of a Fabry-Perot type laser, narrowing or broadening the laser linewidth and reducing the laser chirp. It also can be used for tuning laser emission frequency as the feedback will change the wavelength of the laser. However, optical feedback may also be disadvantageous to semiconductor laser operation. Excessive optical feedback may cause instabilities to the laser where intensity noise increases tremendously. The linewidth enhancement factor, ?? is also affected by the optical feedback. Changes in ? will affect the relation between intensity and phase modulation, AM/FM noise correlation, injection locking, line-shape, linewidth and phase noise. Being able to measure ??will allow the calculation of laser linewidth and consequently the coherence length. Several techniques have been proposed so far for measuring ?, including direct measurement of the sub-threshold optical spectrum as the injected current is varied, analysis of the locking regimes induced by optical injection from a master laser and optical heterodyning methods. The self-mixing interferometer, however, offers a simple and compact solution for measuring the linewidth enhancement factor. In this paper, we measure the linewidth enhancement factor using the self-mixing interferometer based on a VCSEL under different levels of optical feedback. The significant changes of the line-shape and linewidth due to the optical feedback are investigated using an optical homodyne technique and compared to the results obtained using self-mixing.

B4-S5.16
Scattering of Carries in ?-Doped Mn InGaAs Quantum Well with Hole-Mediated Ferromagnetism. (#1234) Ljudmila Shchurova, Vladimir Kulbachinskii; Department of Solid State Physics, Physical Institute of RAS, Moscow, Russian Federation.

Transport properties of ferromagnetic quantum wells have revealed interesting properties resulting from the interplay between carrier transport and magnetic behavior. The ferromagnetic phase with Tc about 400 K was detected in ?-doped Mn GaAs/InxGa1-xAs/GaAs quantum well by SQUID magnetometer. Temperature dependences of sheet resistance, magnetoresistance(magnetic field up to 7 T, and perpendicular to the sample plane) in ?-doped GaAs/InxGa1-xAs/GaAs quantum well have been measured in the temperature range 4.2-300 K. All samples had p-type conductivity and high hole mobility. In the temperature range between 50 and 110K at zero magnetic field a kink in the temperature dependence of sheet resistance is visible. At higher temperatures the resistance increases with temperature. Negative magnetoresistance is observed in a temperature interval 4.2 - 35 K and is the most pronounced at low temperatures (lower 20 K). The magnetoresistance changes from colossal negative to enhanced positive with increasing temperature near 35 K. The calculations of temperature dependence of resistance due to scattering by interface roughness, LA phonons, alloy disorder, ionized impurities and magnetic centers have been carried out. The quantitative consistency of the calculated and of the measured temperature dependence of sheet resistance was obtained. Coulomb scattering, and also spin-flip scattering give comparable contributions to the sheet resistance at temperatures smaller then 50 K. Numerical calculations of magnetoresistance in GaAs(?-Mn)/In0.17Ga0.83As/GaAs quantum wells with low Mn concentrations have been determined. The reasons of occurrence of negative magnetoresistance are explained as the reduction of the spin-flip scattering by aligning spins by magnetic field.

B4-S5.17
Influences of Substrate Temperature on the Surface Planarization of Indium Tin Oxide for Optoelectronics Applications. (#650) Woo-Sun Lee, Gwon-Woo Choi, Yong-Jin Seo; Department of Electrical Engineering, Daebul University, Yeongam County, South Jeolla, Republic of Korea.

Indium tin oxide (ITO) thin films have been attracted intensive interest because of their unique properties of good conductivity, high optical transmittance over the visible region and easy patterning ability. ITO thin films have found many applications in anti-static coatings, thermal heater, solar cells, flat panel displays (FPD), liquid crystal display (LCD), electroluminescent devices, sensors and organic light-emitting diodes (OLED). In this paper, ITO films were deposited on glass substrate by radio frequency (RF) magnetron sputtering method. In order to achieve a high transmittance and a low resistivity of ITO thin film, we examined the various film deposition conditions such as substrate temperature, working pressure, annealing temperature, and deposition time. Next, we performed the chemical mechanical polishing (CMP) in order to improve the surface quality of ITO thin film, and compared the electrical and optical properties of the polished ITO thin film. And then, we studied the correlation between the substrate and annealing temperature and the CMP performances in order to achieve a good stability of ITO thin film for optoelectronics applications through the optimal CMP process. This work was supported by grant No. R01-2006-000-11275-0 from the Basic Research Program of the Korea Science & Engineering Foundation and Korea Research Foundation Grant (KRF-2006-005-J00902).

B4-S5.18
Negative Magnetoresistance Behaviour in Insulating n-type InP and CdSe Semiconductors and Localized Magnetic Moments at Very Low Temperatures. (#98) Abdelhamid El kaaouachi, Rachid Abdia, Abdelhakim Nafidi; Faculty of Sciences, University Ibn Zohr, Agadir, Morocco.

We present results of an experimental study of magnetoresistance (MR) in insulating n-type InP and CdSe samples showing Variable Range Hopping (VRH) conductivity. The MR is found to be negative in a wide range of low temperature (1.5-7 K) and in the range of moderate magnetic fields (0 - 2.1T) for CdSe sample, and in (0.115-2.55 K) and (0-0.35 T) for InP sample. As theories based on quantum interference effects are only valid for very low magnetic fields (B < 0.1 T), we made tentative analysis with a model of localized magnetic moments. The negative MR is quite well approximated by a Langevin function with an effective magnetic moment.

B4-S5.19
Fabrication and Characterization of Nitride Base Photodiodes with Nanostructure. (#1055) Tsair-Chun Liang¹, Shang-Chao Hung², Hsi-Shan Huang¹; ¹Graduate Institute of Electro-Optical Engineering, National Kaohsiung First University of Science and Technology, Kaohsiung City, Taiwan ; ²Department of Information Technology and Communication, Shih Chien University, Kaohsiung, Taiwan.

In this study, Nitride base photodiodes with nanostructure were successfully fabricated by metal-organic chemical vapor deposition (MOCVD) growth; we achieved nanoscale InGaN self-assembled Quantum Dots (QDs) in the well layers of the active region. It was found that the turn on voltage in forward bias and the break down voltage in reverse bias are about 3 and -13.5 V, respectively. The RT PL spectrum peak position for the fabricated InGaN / GaN multi-QDs p-n junction PDs is located at 464.6 nm and FWHM is 24.2 nm. Furthermore, with 1, 2, and 3V applied bias, the maximum responsivity of the fabricated multi-QDs p-n junction PD was observed at 350 nm, and the minimum of spectral response was measured at 465 nm. It was also found that the responsivity was nearly a constant from 390 to 440 nm It seems to suggest that the spectral response in the range of 390- 440nm is due to the effect of the InGaN dots in a well active layers. Keywords: MOCVD; nanostructure; Photodiodes; Quantum Dots; QCSE :

B4-S5.20
Dielectric Study and Thermodynamic Properties of Fluorobenzene and Liquid Crystal Structure in Polar and Non-Polar Solvent at Different Temperatures. (#1380) Amid Ranjkesh, Department of Chemistry, Guilan University, Iran.

The valuable information about the nature and strength of interactions in liquid solutions, over a range of mole fractions, can be obtained using dielectric studies. A large amount of investigation has been carried out in recent years on the dielectric measurements of polar solutions with various molecular structure and different functional groups, in order to understand and provide further information about the dielectric behavior and solution chemistry of chosen compounds. Experimental results of dielectric investigations for solutions of Fluorobenzene, FB, and its mesogenic derivative (1-fluoro-4-(4-pentylcyclohexyl) benzene, FPCHB, in 1,4-dioxane and 1-butanol were reported for various mole fractions and temperatures. The molecular dipole moments were determined using Guggenheim-Debye and Higasi methods in the temperature range of (298.2-318.2) K.

B4-S5.21
Various Annealing Methods for Activation of Arsenic in Molecular Beam Epitaxy Grown HgCdTe. (#844) Gordon Keen Onn Tsen, Jing Zhang, Charles A Musca, John M Dell, Jarek Antoszewski, Lorenzo Faraone; School of Electrical Electronic and Computer Engineering, The University of Western Australia, Australia.

The semiconductor compound, Mercury Cadmium Telluride (HgCdTe), currently dominates the field of infrared detection. By varying the Cd to Hg mole fraction during the growth process, the material can be tailored to respond to spectral wavelengths of interest in the infrared regime. The preferred growth method for HgCdTe is Molecular Beam Epitaxy (MBE) due to the controllable growth rate achievable and the low growth temperatures required for Hg based structures that require abrupt interfaces. To achieve higher performance, fabricated infrared detectors are normally operated in the photovoltaic mode which requires a stable and reproducible technology in terms of extrinsic doping of the material during growth. While extrinsic n-type doping using indium and/or iodine during MBE growth is now a routine process, to date, there has not been a consistent in-situ MBE doping approach to obtain extrinsically p-type material. Out of the many potential p-type dopants possible, arsenic has been the most extensively studied due to its low diffusivity in HgCdTe. However, under optimum MBE growth conditions, incorporated arsenic tends to reside on the cation sublattice sites forming complexes which generally result in as-grown material having n-type characteristics. The conventional approach for arsenic activation is a high temperature post growth anneal under Hg saturated conditions to move arsenic to the anion sublattice sites where they act as p-type dopants. This anneal is undesirable as structural defects may be introduced proving detrimental to detector performance. Furthermore, the high temperatures involved may cause interdiffusion in the material, altering composition and doping, hence posing a limit towards the fabrication of more advance detectors such as heterostructures or superlattices which employ multiple p-n junctions. To fully utilise the benefits of low temperature MBE growth, methods must be devised to either obtain p-type material as-grown by modifying growth methods and conditions or using lower temperature anneals under varying Hg pressures so as to obtain the same conditions as the high temperature anneal for arsenic activation. The latter approach is the main subject of discussion in this paper. In this study, several arsenic doped HgCdTe samples were grown in-house by MBE using an arsenic cracker cell as the dopant source. The samples underwent various annealing approaches that include varying Hg partial pressures and anneal duration. Electrical characterisation of the material will comprise of Fourier Transform Infrared Radiation (FTIR), Secondary Ion Mass Spectrometry (SIMS) and Magneto-Transport Hall measurements coupled with the Quantitative Mobility Spectrum Analysis (QMSA). The effectiveness of each anneal will be studied closely with optimum annealing strategies for arsenic activation to be proposed.