The Experts below are selected from a list of 39723 Experts worldwide ranked by ideXlab platform
Andrea Leto - One of the best experts on this subject based on the ideXlab platform.
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spatially resolved residual stress assessments of gan film on Sapphire Substrate by cathodoluminescence piezospectroscopy
Journal of Applied Physics, 2008Co-Authors: Giuseppe Pezzotti, Alessandro Alan Porporati, Andrea LetoAbstract:Two cathodoluminescence piezospectroscopic (CL/PS) approaches for measuring the residual stress distribution in thin films are critically examined and compared using an intrinsic GaN film sample (2.5μm in thickness) grown on a (0001)-oriented Sapphire Substrate. The first approach invokes an analytical model to fit experimental stress distributions as retrieved in both film and Substrate at the edge of an artificially created cross section of the sample. Such an edge-stress distribution takes into account both the thermal expansion mismatch between the film and Substrate and the mechanistics of film growth process. In the second approach, we directly and nondestructively measure the bulk residual stress field from the sample top surface on the film side using an increase in electron beam voltage (maintaining a constant beam power) as a means for screening the film subsurface. In this latter case, the combined effects of self-absorption and misfit dislocations on the GaN spectrum severely affect the CL/PS ...
B Monemar - One of the best experts on this subject based on the ideXlab platform.
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effect of Sapphire Substrate thickness on the curvature of thick gan films grown by hydride vapor phase epitaxy
Journal of Applied Physics, 2007Co-Authors: T Paskova, Linda Becker, T Bottcher, D Hommel, Plamen Paskov, B MonemarAbstract:The effect of Sapphire-Substrate thickness on the curvature and stress in thick hydride vapor phase epitaxial GaN films was studied by high-resolution x-ray diffraction at variable temperatures. The curvature was found to have the maximum value for comparable thicknesses of the film and the Substrate, while the stress at the film surface decreases with increasing film thickness and increases with increasing Substrate thickness, which is in very good agreement with the simulation results. The curvature at the growth temperature was found to be strongly influenced by the value of the intrinsic tensile strain, which is determined by the film/Substrate thickness ratio. © 2007 American Institute of Physics.
Yaju Lee - One of the best experts on this subject based on the ideXlab platform.
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enhanced conversion efficiency of ingan multiple quantum well solar cells grown on a patterned Sapphire Substrate
Applied Physics Letters, 2011Co-Authors: Yaju Lee, M H Lee, Chun Mao Cheng, Chia Hao YangAbstract:This study demonstrated the enhanced conversion efficiency of an indium gallium nitride (InGaN) multiple quantum well (MQW) solar cell fabricated on a patterned Sapphire Substrate (PSS). Compared to conventional solar cells grown on a planar Sapphire Substrate, threading dislocation defects were found to be reduced from 1.28 × 109 to 3.62 × 108 cm−2, leading to an increase in short-circuit current density (JSC = 1.09 mA·cm−2) of approximately 60%. In addition, the open-circuit voltage and fill factor (VOC = 2.05 V; FF = 51%) of the solar cells grown on PSS were nearly identical to those of conventional devices. The enhanced performance is primarily due to improvements in the crystalline quality of the epitaxial layers, reducing the trapping of photogenerated electrons and holes by nonradiative recombination centers in MQW, with a corresponding increase in the transport efficiency of the carriers outside the device.
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study of gan based light emitting diodes grown on chemical wet etching patterned Sapphire Substrate with v shaped pits roughening surfaces
Journal of Lightwave Technology, 2008Co-Authors: Yaju Lee, Haochung Kuo, Shingchung Wang, Kei May Lau, Zupo Yang, A S P Chang, Shawnyu LinAbstract:We investigate the mechanism responding for performance enhancement of gallium nitride (GaN)-based light-emitting diode (LED) grown on chemical wet-etching-patterned Sapphire Substrate (CWE-PSS) with V-Shaped pit features on the top surface. According to temperature-dependent photoluminescence (PL) measurement and the measured external quantum efficiency, the structure can simultaneously enhance both internal quantum efficiency and light extraction efficiency. Comparing to devices grown on planar Sapphire Substrate, the threading dislocation defects of LED grown on CWE-PSS are reduced from 1.28 times 109/cm2 to 3.62 times 108/cm2, leading to a 12.5% enhancement in internal quantum efficiency. In terms of the theoretical computing of radiation patterns, the V-Shaped pits roughening surface can be thought of as a strong diffuser with paraboloidal autocorrelation function, increasing the escape probability of trapped photons and achieving a 20% enhancement in light extraction efficiency. Moreover, according to the measurement of optical diffraction power, CWE-PSS demonstrated superior guided light extraction efficiency than that of planar Sapphire Substrate, thus an extra 7.8% enhancement in light extraction efficiency was obtained. Therefore, comparing to the conventional LED, an overall 45% enhancement in integrated output power was achieved.
Tongchang Zheng - One of the best experts on this subject based on the ideXlab platform.
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in situ self release of thick gan wafer from Sapphire Substrate via graded strain field engineering
Applied Physics Letters, 2014Co-Authors: Jiejun Wu, Hongmei Xu, Tongchang ZhengAbstract:We present a scheme for in situ self-release of thick GaN 2-in. wafer from Sapphire Substrate by engineering the gradient of misfit strains. Release energies of a-, m-, and c-planes of wurtzite GaN are systematically calculated under different biaxial strains by using first-principles method. The results reveal that the c-plane separation will take place under graded strains around −2.8%, where a drastic transition interface of release energy may strongly reduce the strength of c-plane bonding. Based on this mechanism, uniform thick GaN epilayer (>450 μm) is grown on (0001) Sapphire Substrate by hydride vapor phase epitaxy and subjected to a graded compressive strain field by bowing, fulfilling the c-plane separation condition. As a result, high quality free-standing GaN wafer (350 μm) can be achieved by self-release simply during the cooling process.
Jianbin Luo - One of the best experts on this subject based on the ideXlab platform.
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effects of the ultrasonic flexural vibration on the interaction between the abrasive particles pad and Sapphire Substrate during chemical mechanical polishing cmp
Applied Surface Science, 2011Co-Authors: Guoshun Pan, Yuanzhong Lei, Jianbin LuoAbstract:Abstract In this paper, the technique of ultrasonic flexural vibration assisted chemical mechanical polishing (UFV-CMP) was used for Sapphire Substrate CMP. The functions of the polishing pad, the silica abrasive particles, and the chemical additives of the slurry such as pH value regulator and dispersant during the Sapphire's UFV-CMP were investigated. The results showed that the actions of the ultrasonic and silica abrasive particles were the main factors in the Sapphire material removal rate (MMR) and the chemical additives were helpful to decrease the roughness of Sapphire. Then the effects of the flexural vibration on the interaction between the silica abrasive particles, pad and Sapphire Substrate from the kinematics and dynamics were investigated to explain why the MRR of UFV-CMP was bigger than that of the traditional CMP. It indicated that such functions improved the Sapphire's MRR: the increasing of the contact silica particles’ motion path lengths on the Sapphire's surface, the enhancement of the contact force between the contact silica particles and the Sapphire's surface, and the impaction of the suspending silica particles to the Sapphire's surface.
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ultrasonic flexural vibration assisted chemical mechanical polishing for Sapphire Substrate
Applied Surface Science, 2010Co-Authors: Guoshun Pan, Yuanzhong Lei, Jianbin LuoAbstract:Abstract The Sapphire Substrates are polished by traditional chemical mechanical polishing (CMP) and ultrasonic flexural vibration (UFV) assisted CMP (UFV–CMP) respectively with different pressures. UFV–CMP combines the functions of traditional CMP and ultrasonic machining (USM) and has special characteristics, which is that ultrasonic vibrations of the rotating polishing head are in both horizontal and vertical directions. The material removal rates (MRRs) and the polished surface morphology of CMP and UFV–CMP are compared. The MRR of UFV–CMP is two times larger than that of traditional CMP. The surface roughness (root mean square, RMS) of the polished Sapphire Substrate of UFV–CMP is 0.83 A measured by the atomic force microscopy (AFM), which is much better than 2.12 A obtained using the traditional CMP. And the surface flatness of UFV–CMP is 0.12 μm, which is also better than 0.23 μm of the traditional CMP. The results show that UFV–CMP is able to improve the MRR and finished surface quality of the Sapphire Substrates greatly. The material removal and surface polishing mechanisms of Sapphire in UFV–CMP are discussed too.
