Advances in Condensed Matter Physics The latest articles from Hindawi Publishing Corporation © 2015 , Hindawi Publishing Corporation . All rights reserved. Structural and Electronic Properties of GaN (0001)/α-Al2O3 (0001) Interface Wed, 20 May 2015 11:34:49 +0000 Structural and electronic properties of the interface between α-Al2O3 (0001) and GaN (0001) surfaces are investigated through ab initio calculations within the density functional theory. Two different structural models have been investigated interface N(Ga)-terminated. The interface N-terminated GaN surface seems to exhibit the lowest formation energy. The studied interface models are metallic, with the levels at energy spatially confined in the interface region. Our calculations show strong hybridization between atoms in the interface region. M. B. Pereira, E. M. Diniz, and S. Guerini Copyright © 2015 M. B. Pereira et al. All rights reserved. Shape-Dependent Energy of an Elliptical Jellium Background Sun, 17 May 2015 11:33:31 +0000 The jellium model is commonly used in condensed matter physics to study the properties of a two-dimensional electron gas system. Within this approximation, one assumes that electrons move in the presence of a neutralizing background consisting of uniformly spread positive charge. When properties of bulk systems (of infinite size) are studied, shape of the jellium domain is irrelevant. However, the same cannot be said when one is dealing with finite systems of electrons confined in a finite two-dimensional region of space. In such a case, geometry and shape of the jellium background play a role on the overall properties of the system. In this work, we assume that the region where the electrons are confined is represented by a jellium background charge with an elliptical shape. It is shown that, in this case, the Coulomb self-energy of the elliptically shaped region can be exactly calculated in closed analytical form by using suitable mathematical transformations. The results obtained reveal the external influence of geometry/shape on the properties of two-dimensional systems of few electrons confined to a small finite region of space. Orion Ciftja, LeDarion Escamilla, and Ryan Mills Copyright © 2015 Orion Ciftja et al. All rights reserved. Band Structure Analysis of La0.7Sr0.3MnO3 Perovskite Manganite Using a Synchrotron Thu, 14 May 2015 08:34:54 +0000 Oxide semiconductors and their application in next-generation devices have received a great deal of attention due to their various optical, electric, and magnetic properties. For various applications, an understanding of these properties and their mechanisms is also very important. Various characteristics of these oxides originate from the band structure. In this study, we introduce a band structure analysis technique using a soft X-ray energy source to study a (LSMO) oxide semiconductor. The band structure is formed by a valence band, conduction band, band gap, work function, and electron affinity. These can be determined from secondary electron cut-off, valence band spectrum, O 1s core electron, and O K-edge measurements using synchrotron radiation. A detailed analysis of the band structure of the LSMO perovskite manganite oxide semiconductor thin film was established using these techniques. Hong-Sub Lee and Hyung-Ho Park Copyright © 2015 Hong-Sub Lee and Hyung-Ho Park. All rights reserved. Influence of Size Effect on the Electronic and Elastic Properties of Graphane Nanoflakes: Quantum Chemical and Empirical Investigations Mon, 04 May 2015 09:34:36 +0000 By application of empirical method it is found that graphene nanoflake (graphane) saturated by hydrogen is not elastic material. In this case, the modulus of the elastic compression of graphane depends on its size, allowing us to identify the linear parameters of graphane with maximum Young’s modulus for this material. The electronic structure of graphane nanoflakes was calculated by means of the semiempirical tight-binding method. It is found that graphane nanoflakes can be characterized as dielectric. The energy gap of these particles decreases with increasing of the length tending to a certain value. At the same time, the ionization potential of graphane also decreases. A comparative analysis of the calculated values with the same parameters of single-walled nanotubes is performed. A. S. Kolesnikova, M. M. Slepchenkov, M. F. Lin, and O. E. Glukhova Copyright © 2015 A. S. Kolesnikova et al. All rights reserved. Si- and Ge-Based Electronic Devices Mon, 27 Apr 2015 12:44:44 +0000 Yi Zhao, Rui Zhang, Jiwu Lu, and Wenfeng Zhang Copyright © 2015 Yi Zhao et al. All rights reserved. Characteristics and Breakdown Behaviors of Polysilicon Resistors for High Voltage Applications Mon, 27 Apr 2015 08:09:28 +0000 With the rapid development of the power integrated circuit technology, polysilicon resistors have been widely used not only in traditional CMOS circuits, but also in the high voltage applications. However, there have been few detailed reports about the polysilicon resistors’ characteristics, like voltage and temperature coefficients and breakdown behaviors which are critical parameters of high voltage applications. In this study, we experimentally find that the resistance of the polysilicon resistor with a relatively low doping concentration shows negative voltage and temperature coefficients, while that of the polysilicon resistor with a high doping concentration has positive voltage and temperature coefficients. Moreover, from the experimental results of breakdown voltages of the polysilicon resistors, it could be deduced that the breakdown of polysilicon resistors is thermally rather than electrically induced. We also proposed to add an N-type well underneath the oxide to increase the breakdown voltage in the vertical direction when the substrate is P-type doped. Xiao-Yu Tang and Ke Dong Copyright © 2015 Xiao-Yu Tang and Ke Dong. All rights reserved. Transformation of Holes Emission Paths under Negative Bias Temperature Stress in Deeply Scaled pMOSFETs Mon, 27 Apr 2015 06:25:24 +0000 We examine the impact of negative bias temperature (NBT) stress on the fluctuations in and for deeply scaled pMOSFETs and find that the relative high NBT stress triggers -RTN and -step. Through the analysis of the field dependence of emission constant and the carrier separation measurement, it is found that under the relative high NBT stress some traps keep charged state for very long time, as observing step-like behaviors in , while other traps emit charged holes to the gate side through TAT process, which originate both -step and ID-RTN. Yiming Liao, Xiaoli Ji, Qiang Guo, and Feng Yan Copyright © 2015 Yiming Liao et al. All rights reserved. DC Characteristics Optimization of a Double G-Shield 50 V RF LDMOS Thu, 23 Apr 2015 14:02:39 +0000 An N-type 50 V RF LDMOS with a RESURF (reduced surface field) structure of dual field plates (grounded shield, or G-shield) was investigated. The effect of the two field plates and N-drift region, including the junction depth and dopant concentration, on the DC characteristics was analyzed by employing the Taurus TCAD device simulator. A high BV (breakdown voltage) can be achieved while keeping a low (on-resistance). The simulation results show that the N-drift region dopant concentration has an obvious effect on the BV and and the junction depth affected these values less. There is an optimized length for the second field plate for a given dopant concentration of the N-drift region. Both factors should be optimized together to determine the best DC characteristics. Meanwhile, the effect of the first field plate on the BV and can be ignored. According to the simulation results, 50 V RF LDMOS with an optimized RESURF structure of a double G-shield was fabricated using 0.35 µm technologies. The measurement data show the same trend as the TCAD simulation, where a BV of 118 V and of 26 ohm·mm were achieved. Xiangming Xu, Pengliang Ci, Xiaoyu Tang, Jing Shi, Zhengliang Zhou, Jingfeng Huang, Peng-Fei Wang, and David Wei Zhang Copyright © 2015 Xiangming Xu et al. All rights reserved. Design of a Novel W-Sinker RF LDMOS Thu, 23 Apr 2015 13:19:49 +0000 A novel RF LDMOS device structure and corresponding manufacturing process are presented in this paper. Deep trench W-sinker (tungsten sinker) is employed in this technology to replace the traditional heavily doped diffusion sinker which can shrink chip size of the LDMOS transistor by more than 30% and improve power density. Furthermore, the W-sinker structure reduces the parasitic resistance and inductance and improves thermal conductivity of the device as well. Combined with the adoption of the techniques, like grounded shield, step gate oxide, LDD optimization, and so forth, an advanced technology for RF LDMOS based on conventional 0.35 m CMOS technology is well established. An power amplifier product with frequency range of 1.8–2.1 GHz is developed for the application of 4G LTE base station and industry leading performance is achieved. The qualification results show that the device reliability and ruggedness can also meet requirement of the application. Xiangming Xu, Han Yu, Jingfeng Huang, Chun Wang, Wei Ji, Zhengliang Zhou, Ying Cai, Yong Wang, Pingliang Li, Peng-Fei Wang, and David Wei Zhang Copyright © 2015 Xiangming Xu et al. All rights reserved. High-Electron-Mobility SiGe on Sapphire Substrate for Fast Chipsets Thu, 23 Apr 2015 12:46:10 +0000 High-quality strain-relaxed SiGe films with a low twin defect density, high electron mobility, and smooth surface are critical for device fabrication to achieve designed performance. The mobilities of SiGe can be a few times higher than those of silicon due to the content of high carrier mobilities of germanium (p-type Si: 430 cm2/V·s, p-type Ge: 2200 cm2/V·s, n-type Si: 1300 cm2/V·s, and n-type Ge: 3000 cm2/V·s at 1016 per cm3 doping density). Therefore, radio frequency devices which are made with rhombohedral SiGe on -plane sapphire can potentially run a few times faster than RF devices on SOS wafers. NASA Langley has successfully grown highly ordered single crystal rhombohedral epitaxy using an atomic alignment of the direction of cubic SiGe on top of the direction of the sapphire basal plane. Several samples of rhombohedrally grown SiGe on -plane sapphire show high percentage of a single crystalline over 95% to 99.5%. The electron mobilities of the tested samples are between those of single crystals Si and Ge. The measured electron mobility of 95% single crystal SiGe was 1538 cm2/V·s which is between 350 cm2/V·s (Si) and 1550 cm2/V·s (Ge) at 6 × 1017/cm3 doping concentration. Hyun Jung Kim, Yeonjoon Park, Hyung Bin Bae, and Sang H. Choi Copyright © 2015 Hyun Jung Kim et al. All rights reserved. Responsivity Enhanced NMOSFET Photodetector Fabricated by Standard CMOS Technology Thu, 23 Apr 2015 12:41:33 +0000 Increasing the responsivity is one of the important issues for a photodetector. In this paper, we demonstrate an improved NMOSFET photodetector by using deep-n-well (DNW) structure which can improve the responsivity of the photodetector significantly. The experimental results show that the responsivity can be enhanced greatly by the DNW structure and is much larger than the previous work when DNW is biased with 0.5 V, while the dark current exhibits almost no increase. Further characterization indicates that the diode formed by the bulk and DNW can efficiently absorb photons and has a large gain factor of the photocurrent especially under low light condition, which gives a more promising application for the detector to detect the weak light. Fuwei Wu, Xiaoli Ji, and Feng Yan Copyright © 2015 Fuwei Wu et al. All rights reserved. The Investigation of Field Plate Design in 500 V High Voltage NLDMOS Thu, 23 Apr 2015 12:38:40 +0000 This paper presents a 500 V high voltage NLDMOS with breakdown voltage () improved by field plate technology. Effect of metal field plate (MFP) and polysilicon field plate (PFP) on breakdown voltage improvement of high voltage NLDMOS is studied. The coeffect of MFP and PFP on drain side has also been investigated. A 500 V NLDMOS is demonstrated with a 37 μm drift length and optimized MFP and PFP design. Finally the breakdown voltage 590 V and excellent on-resistance performance ( = 7.88 ohm * mm2) are achieved. Donghua Liu, Xiangming Xu, Feng Jin, Wenting Duan, Huihui Wang, Jing Shi, Yuan Yao, Jun Hu, Wensheng Qian, Pengfei Wang, and David Wei Zhang Copyright © 2015 Donghua Liu et al. All rights reserved. Interface Engineering and Gate Dielectric Engineering for High Performance Ge MOSFETs Thu, 23 Apr 2015 12:24:09 +0000 In recent years, germanium has attracted intensive interests for its promising applications in the microelectronics industry. However, to achieve high performance Ge channel devices, several critical issues still have to be addressed. Amongst them, a high quality gate stack, that is, a low defect interface layer and a dielectric layer, is of crucial importance. In this work, we first review the existing methods of interface engineering and gate dielectric engineering and then in more detail we discuss and compare three promising approaches (i.e., plasma postoxidation, high pressure oxidation, and ozone postoxidation). It has been confirmed that these approaches all can significantly improve the overall performance of the metal-oxide-semiconductor field effect transistor (MOSFET) device. Jiabao Sun and Jiwu Lu Copyright © 2015 Jiabao Sun and Jiwu Lu. All rights reserved. Ozone Treatment Improved the Resistive Switching Uniformity of HfAlO2 Based RRAM Devices Thu, 23 Apr 2015 11:55:12 +0000 HfAlO2 based resistive random access memory (RRAM) devices were fabricated using atomic layer deposition by modulating deposition cycles for HfO2 and Al2O3. Effect of ozone treatment on the resistive switching uniformity of HfAlO2 based RRAM devices was investigated. Compared to the as-fabricated devices, the resistive switching uniformity of HfAlO2 based RRAM devices with the ozone treatment is significantly improved. The uniformity improvement of HfAlO2 based RRAM devices is related to changes in compositional and structural properties of the HfAlO2 resistive switching film with the ozone treatment. Lifeng Liu, Yi Hou, Weibing Zhang, Dedong Han, and Yi Wang Copyright © 2015 Lifeng Liu et al. All rights reserved. Retracted: Quadrupole Excitation in Tunnel Splitting Oscillation in Nanoparticle Mn12 Thu, 16 Apr 2015 07:34:27 +0000 Advances in Condensed Matter Physics Copyright © 2015 Advances in Condensed Matter Physics. All rights reserved. Chemical Reduction of Nd1.85Ce0.15CuO4−δ Powders in Supercritical Sodium Ammonia Solutions Wed, 08 Apr 2015 13:10:58 +0000 Nd1.85Ce0.15CuO4−δ powders are chemically reduced in supercritical sodium ammonia solutions from room temperature to 350°C. The crystallographic structure of the reduced powders is investigated from Rietveld refinement of X-ray powder diffraction. The atomic positions are maintained constant within experimental errors while temperature factors of all atoms increase significantly after the chemical treatments, especially of Nd/Ce atoms. The ammonothermally reduced Nd1.85Ce0.15CuO4−δ powders show diamagnetic below 24 K which is contributed to the lower oxygen content and higher temperature factors of atoms in the treated compound. The ammonothermal method paves a new way to reduce oxides in supercritical solutions near room temperature. Yasmin Dias, Hui Wang, Haiqing Zhou, Feng Lin, and Yucheng Lan Copyright © 2015 Yasmin Dias et al. All rights reserved. A Generalization of Electromagnetic Fluctuation-Induced Casimir Energy Wed, 25 Mar 2015 12:48:31 +0000 Intermolecular forces responsible for adhesion and cohesion can be classified according to their origins; interactions between charges, ions, random dipole—random dipole (Keesom), random dipole—induced dipole (Debye) are due to electrostatic effects; covalent bonding, London dispersion forces between fluctuating dipoles, and Lewis acid-base interactions are due to quantum mechanical effects; pressure and osmotic forces are of entropic origin. Of all these interactions, the London dispersion interaction is universal and exists between all types of atoms as well as macroscopic objects. The dispersion force between macroscopic objects is called Casimir/van der Waals force. It results from alteration of the quantum and thermal fluctuations of the electrodynamic field due to the presence of interfaces and plays a significant role in the interaction between macroscopic objects at micrometer and nanometer length scales. This paper discusses how fluctuational electrodynamics can be used to determine the Casimir energy/pressure between planar multilayer objects. Though it is confirmation of the famous work of Dzyaloshinskii, Lifshitz, and Pitaevskii (DLP), we have solved the problem without having to use methods from quantum field theory that DLP resorted to. Because of this new approach, we have been able to clarify the contributions of propagating and evanescent waves to Casimir energy/pressure in dissipative media. Yi Zheng Copyright © 2015 Yi Zheng. All rights reserved. Quadrupole Excitations in Magnetic Susceptibility of Magnetic Nanoparticle Fe8 Tue, 24 Mar 2015 13:52:22 +0000 Magnetic susceptibility dependence on temperatures in different magnetic fields will be discussed. Until today, to calculate magnetization and magnetic susceptibility, only dipole excitations have been considered, but, due to the symmetry of operators in Hamiltonian and also to achieve more accuracy, other multiple excitations must be taken into account too. To this end, here, both dipole and quadruple excitations are considered and then the resulting curves will be plotted in presence of different magnetic fields. Finally, seen that the graphs obtained using the multipole excitations more accurately with results taken by experimental data. Yousef Yousefi Copyright © 2015 Yousef Yousefi. All rights reserved. Low-Dimensional Semiconductor Structures for Optoelectronic Applications Tue, 24 Mar 2015 09:20:40 +0000 Wei Lu, Hong Chen, Weida Hu, Guofeng Song, Wen Lei, and Ying Fu Copyright © 2015 Wei Lu et al. All rights reserved. Rebirth of Liquid Crystals for Sensoric Applications: Environmental and Gas Sensors Mon, 23 Mar 2015 08:39:27 +0000 Films and droplets of liquid crystals may soon become an essential part of sensitive environmental sensors and detectors of volatile organic compounds (VOCs) in the air. In this paper a short overview of recent progress in the area of sensors based on liquid crystals is presented, along with the studies of low molar mass liquid crystals as gas sensors. The detection of VOCs in the air may rely on each of the following effects sequentially observed one after the other: (i) slight changes in orientation and order parameter of liquid crystal, (ii) formation of bubbles on the top of the liquid crystalline droplet, and (iii) complete isotropisation of the liquid crystal. These three stages can be easily monitored by a photo camera and/or optical microscopy. Detection limits corresponding to the first stage are typically lower by a factor of at least 3–6 than detection limits corresponding to isotropisation. The qualitative model taking into account the reorientation of liquid crystals is presented to account for the observed changes. P. V. Shibaev, M. Wenzlick, J. Murray, A. Tantillo, and J. Howard-Jennings Copyright © 2015 P. V. Shibaev et al. All rights reserved. Tuning Rheological Performance of Silica Concentrated Shear Thickening Fluid by Using Graphene Oxide Mon, 23 Mar 2015 08:39:14 +0000 The addition of a small amount of graphene oxide into a traditional colloidal silica-based shear thickening fluid (STF) can lead to a significant change in viscosity, critical shear rate, storage modulus, and loss modulus of STF. This finding provides an effective way to prepare stronger and light-weight STFs. Wenchao Huang, Yanzhe Wu, Ling Qiu, Cunku Dong, Jie Ding, and Dan Li Copyright © 2015 Wenchao Huang et al. All rights reserved. Synthesis, Characterization, and Photoluminescence on the Glass Doped with AgInS2 Nanocrystals Sun, 22 Mar 2015 14:12:03 +0000 We demonstrated a synthetic process on the glass doped with AgInS2 nanocrystals through sol-gel method under a controlled atmosphere. X-ray powder diffraction and X-ray photoelectron spectra revealed that the AgInS2 crystalline phase had formed in the glass matrix. Transmittance electron microscopy showed that these AgInS2 crystals had spherical shape and good dispersed form in the glass matrix, and their diameter distribution was mainly focused on three size regions. Furthermore, the glass doped with AgInS2 nanocrystals exhibited three photoluminescence peaks located at 1.83 eV, 2.02 eV, and 2.21 eV, which were ascribed to the introduction of AgInS2 nanocrystals in the glass. Dewu Yin, Lang Pei, Zhen Liu, Xinyu Yang, Weidong Xiang, and Xiyan Zhang Copyright © 2015 Dewu Yin et al. All rights reserved. Analysis of Low Dimensional Nanoscaled Inversion-Mode InGaAs MOSFETs for Next-Generation Electrical and Photonic Applications Sun, 22 Mar 2015 10:53:02 +0000 The electrical characteristics of In0.53Ga0.47As MOSFET grown with Si interface passivation layer (IPL) and high gate oxide HfO2 layer have been investigated in detail. The influences of Si IPL thickness, gate oxide HfO2 thickness, the doping depth, and concentration of source and drain layer on output and transfer characteristics of the MOSFET at fixed gate or drain voltages have been individually simulated and analyzed. The determination of the above parameters is suggested based on their effect on maximum drain current, leakage current, saturated voltage, and so forth. It is found that the channel length decreases with the increase of the maximum drain current and leakage current simultaneously. Short channel effects start to appear when the channel length is less than 0.9 μm and experience sudden sharp increases which make device performance degrade and reach their operating limits when the channel length is further lessened down to 0.5 μm. The results demonstrate the usefulness of short channel simulations for designs and optimization of next-generation electrical and photonic devices. C. H. Yu, X. Y. Chen, X. D. Luo, W. W. Xu, and P. S. Liu Copyright © 2015 C. H. Yu et al. All rights reserved. Shell Thickness-Dependent Strain Distributions of Confined Au/Ag and Ag/Au Core-Shell Nanoparticles Sun, 22 Mar 2015 10:03:23 +0000 The shell thickness-dependent strain distributions of the Au/Ag and Ag/Au core-shell nanoparticles embedded in Al2O3 matrix have been investigated by finite element method (FEM) calculations, respectively. The simulation results clearly indicate that there is a substantial strain applied on both the Au/Ag and Ag/Au core-shell nanoparticles by the Al2O3 matrix. For the Au/Ag nanoparticles, it can be found that the compressive strain existing in the shell is stronger than that on the center of core and reaches the maximum at the interface between the shell and core. In contrast, for the Ag/Au nanoparticles, the compressive strain applied on the core is much stronger than that at the interface and that in the shell. With the shell thickness increasing, both of the strains in the Au/Ag and Ag/Au nanoparticles increase as well. However, the strain gradient in the shell decreases gradually with the increasing of the shell thickness for both of Ag/Au ad Au/Ag nanoparticles. These results provide an effective method to manipulate the strain distributions of the Au/Ag and Ag/Au nanoparticles by tuning the thickness of the shell, which can further have significant influences on the microstructures and physical properties of Au/Ag and Ag/Au nanoparticles. Feng Liu, Honghua Huang, Ying Zhang, Ting Yu, Cailei Yuan, and Shuangli Ye Copyright © 2015 Feng Liu et al. All rights reserved. Modeling and Simulation of a Resonant-Cavity-Enhanced InGaAs/GaAs Quantum Dot Photodetector Sun, 22 Mar 2015 09:16:18 +0000 We simulated and analyzed a resonant-cavity-enhancedd InGaAs/GaAs quantum dot n-i-n photodiode using Crosslight Apsys package. The resonant cavity has a distributed Bragg reflector (DBR) at one side. Comparing with the conventional photodetectors, the resonant-cavity-enhanced photodiode (RCE-PD) showed higher detection efficiency, faster response speed, and better wavelength selectivity and spatial orientation selectivity. Our simulation results also showed that when an AlAs layer is inserted into the device structure as a blocking layer, ultralow dark current can be achieved, with dark current densities 0.0034 A/cm at 0 V and 0.026 A/cm at a reverse bias of 2 V. We discussed the mechanism producing the photocurrent at various reverse bias. A high quantum efficiency of 87.9% was achieved at resonant wavelength of 1030 nm with a FWHM of about 3 nm. We also simulated InAs QD RCE-PD to compare with InGaAs QD. At last, the photocapacitance characteristic of the model has been discussed under different frequencies. W. W. Wang, F. M. Guo, and Y. Q. Li Copyright © 2015 W. W. Wang et al. All rights reserved. Modeling and Design of Graphene GaAs Junction Solar Cell Sun, 22 Mar 2015 09:02:29 +0000 Graphene based GaAs junction solar cell is modeled and investigated by Silvaco TCAD tools. The photovoltaic behaviors have been investigated considering structure and process parameters such as substrate thickness, dependence between graphene work function and transmittance, and n-type doping concentration in GaAs. The results show that the most effective region for photo photogenerated carriers locates very close to the interface under light illumination. Comprehensive technological design for junction yields a significant improvement of power conversion efficiency from 0.772% to 2.218%. These results are in good agreement with the reported experimental work. Yawei Kuang, Yushen Liu, Yulong Ma, Jing Xu, Xifeng Yang, Xuekun Hong, and Jinfu Feng Copyright © 2015 Yawei Kuang et al. All rights reserved. Photoelectric Characteristics of Double Barrier Quantum Dots-Quantum Well Photodetector Sun, 22 Mar 2015 08:54:53 +0000 The photodetector based on double barrier AlAs/GaAs/AlAs heterostructures and a layer self-assembled InAs quantum dots and In0.15Ga0.85As quantum well (QW) hybrid structure is demonstrated. The detection sensitivity and detection ability under weak illuminations have been proved. The dark current of the device can remain at 0.1 pA at 100 K, even lower to  A, at bias of −1.35 V. Its current responsivity can reach about  A/W when 1 pw 633 nm light power and −4 V bias are added. Meanwhile a peculiar amplitude quantum oscillation characteristic is observed in testing. A simple model is used to qualitatively describe. The results demonstrate that the InAs monolayer can effectively absorb photons and the double barrier hybrid structure with quantum dots in well can be used for low-light-level detection. M. J. Wang, F. Y. Yue, and F. M. Guo Copyright © 2015 M. J. Wang et al. All rights reserved. Determination of Temperature-Dependent Stress State in Thin AlGaN Layer of AlGaN/GaN HEMT Heterostructures by Near-Resonant Raman Scattering Sun, 22 Mar 2015 08:54:43 +0000 The temperature-dependent stress state in the AlGaN barrier layer of AlGaN/GaN heterostructure grown on sapphire substrate was investigated by ultraviolet (UV) near-resonant Raman scattering. Strong scattering peak resulting from the A1(LO) phonon mode of AlGaN is observed under near-resonance condition, which allows for the accurate measurement of Raman shifts with temperature. The temperature-dependent stress in the AlGaN layer determined by the resonance Raman spectra is consistent with the theoretical calculation result, taking lattice mismatch and thermal mismatch into account together. This good agreement indicates that the UV near-resonant Raman scattering can be a direct and effective method to characterize the stress state in thin AlGaN barrier layer of AlGaN/GaN HEMT heterostructures. Yanli Liu, Xifeng Yang, Dunjun Chen, Hai Lu, Rong Zhang, and Youdou Zheng Copyright © 2015 Yanli Liu et al. All rights reserved. Experimental Determination of Effective Minority Carrier Lifetime in HgCdTe Photovoltaic Detectors Using Optical and Electrical Methods Sun, 22 Mar 2015 08:48:42 +0000 This paper presents experiment measurements of minority carrier lifetime using three different methods including modified open-circuit voltage decay (PIOCVD) method, small parallel resistance (SPR) method, and pulse recovery technique (PRT) on pn junction photodiode of the HgCdTe photodetector array. The measurements are done at the temperature of operation near 77 K. A saturation constant background light and a small resistance paralleled with the photodiode are used to minimize the influence of the effect of junction capacitance and resistance on the minority carrier lifetime extraction in the PIOCVD and SPR measurements, respectively. The minority carrier lifetime obtained using the two methods is distributed from 18 to 407 ns and from 0.7 to 110 ns for the different Cd compositions. The minority carrier lifetime extracted from the traditional PRT measurement is found in the range of 4 to 20 ns for . From the results, it can be concluded that the minority carrier lifetime becomes longer with the increase of Cd composition and the pixels dimensional area. Haoyang Cui, Jialin Wang, Chaoqun Wang, Can Liu, Kaiyun Pi, Xiang Li, Yongpeng Xu, and Zhong Tang Copyright © 2015 Haoyang Cui et al. All rights reserved. Photoresponse of Long-Wavelength AlGaAs/GaAs Quantum Cascade Detectors Thu, 19 Mar 2015 14:21:09 +0000 We study the photoresponse and photocurrents of long-wavelength infrared quantum cascade detectors (QCDs) based on AlGaAs/GaAs material system. The photocurrent spectra were measured at different temperatures from 20 K to 100 K with a low noise Fourier transforming infrared spectrometer. The main response peak appeared at 8.9 μm while four additional response peaks from 4.5 μm to 10.1 μm were observed as well. We confirmed that the photocurrent comes from phonon assisted tunneling and the multipeak behavior comes from the complicated optical transition in the quantum cascade structure. This work is valuable for the future design and optimization of QCD devices. Liang Li and Dayuan Xiong Copyright © 2015 Liang Li and Dayuan Xiong. All rights reserved.