Systematic study of epitaxy growth uniformity in a specific MOCVD reactor

Gallium nitride (GaN) is a direct bandgap semiconductor widely used in bright light‐emitting diodes (LEDs). Thin‐film GaN is grown by metal‐organic chemical vapour deposition (MOCVD) technique. Reliability, efficiency and durability of LEDs are influenced critically by the quality of GaN films. In this report, a systematic study has been performed to investigate and optimize the growth process. Fluid flow, heat transfer and chemical reactions are calculated for a specific close‐coupled showerhead (CCS) MOCVD reactor. Influences of reactor dimensions and growth parameters have been examined after introducing the new conceptions of growth uniformity and growth efficiency. It is found that GaN growth rate is mainly affected by the concentration of (CH3)3Ga:NH3 on the susceptor, while growth uniformity is mainly influenced by the recirculating flows above the susceptor caused by natural convection. Effect of gas inlet temperature and the susceptor temperature over the growth rate can be explained by two competing mechanisms. High growth efficiency can be achieved by optimizing the reactor design.     

氧化镓的同步辐射研究

 利用金刚石对顶砧（DAC）高压装置产生高压，使用体积比为16∶3∶1的甲醇、乙醇和水混合液作为传压介质，通过原位高压同步辐射技术对氧化镓的高压行为进行了研究（0～42.5 GPa）。实验发现在室温下13.3 GPa压力附近，单斜结构的氧化镓发生了结构相变，变成三角结构。相变后镓离子由原来同时位于由氧离子围成的四面体和八面体的中心位置变成只位于八面体的中心位置。卸压后的X射线衍射谱表明，氧化镓又恢复为单斜结构，该相变为可逆相变。     

Self-screening of the polarized electric field in wurtzite gallium nitride along [0001] direction

The strong polarization effect of GaN-based materials is widely used in high-performance devices such as white-light-emitting diodes (white LEDs), high electron mobility transistors (HEMTs), and GaN polarization superjunctions. However, the current researches on the polarization mechanism of GaN-based materials are not sufficient. In this paper, we studied the influence of polarization on electric field and energy band characteristics of Ga-face GaN bulk materials by using a combination of theoretical analysis and semiconductor technology computer-aided design (TCAD) simulation. The self-screening effect in Ga-face bulk GaN under ideal and non-ideal conditions is studied respectively. We believe that the formation of high-density two-dimensional electron gas (2DEG) in GaN is the accumulation of screening charges. We also clarify the source and accumulation of the screening charges caused by the GaN self-screening effect in this paper and aim to guide the design and optimization of high-performance GaN-based devices.     

确定磁性体在绝热磁化过程中达到最高温度的方法

在磁性体磁化过程中, 决定其能够达到的最高温度, 对磁热材料的优化选取是重要的. 本文以钆镓石榴石(Gd₃Ga₅O₁₂) 为例, 根据高磁场下趋近饱和定律的思想, 给出了低温、超强磁场下, Gd₃Ga₅O₁₂晶体等效磁化率的定量形式. 在外磁场从0---40 T范围内, 计算了该晶体的磁熵变、声子熵变以及磁性体温度随外磁场的变化, 结果均与实验值符合较好. 利用声子熵变与饱和磁熵变曲线交点的唯一性, 给出了在磁性体磁化过程中, 确定其温度达到最大值的方法, 预言了Gd₃Ga₅O₁₂晶体在绝热磁化过程中达到的最高温度为64.7K. 该方法还可以对所加外磁场大小进行预言或估计.     

A study of GaN MOSFETs with atomic-layer-deposited Al2O3 as the gate dielectric

Accumulation-type GaN metal-oxide-semiconductor field-effect transistors (MOSFETs) with atomic-layer-deposited Al₂O₃ gate dielectrics are fabricated. The device, with atomic-layer-deposited Al₂O₃ as the gate dielectric, presents a drain current of 260 mA/mm and a broad maximum transconductance of 34 mS/mm, which are better than those reported previously with Al₂O₃ as the gate dielectric. Furthermore, the device shows negligible current collapse in a wide range of bias voltages, owing to the effective passivation of the GaN surface by the Al₂O₃ film. The gate drain breakdown voltage is found to be about 59.5 V, and in addition the channel mobility of the n-GaN layer is about 380 cm²/Vs, which is consistent with the Hall result, and it is not degraded by atomic-layer-deposition Al₂O₃ growth and device fabrication.     

Electrical and structural properties of Pd/V/n‐type InP (111) Schottky structure as a function of annealing temperature

Palladium/Vanadium (Pd/V) Schottky structures are fabricated on n‐type InP (100) and the electrical, structural and surface morphological characteristics have been studied at different annealing temperatures. The extracted barrier height of as‐deposited Pd/V/n‐InP Schottky diode is 0.59 eV (I–V) and 0.79 eV (C–V), respectively. However, the Schottky barrier height of the Pd/V Schottky contact slightly increases to 0.61 eV (I–V) and 0.84 eV (C–V) when the contact is annealed at 200 °C for 1 min. It is observed that the Schottky barrier height of the contact slightly decreases after annealing at 300, 400 and 500 °C for 1 min in N₂ atmosphere. From the above observations, it is clear that the electrical characteristics of Pd/V Schottky contacts improve after annealing at 200 °C. This indicates that the optimum annealing temperature for the Pd/V Schottky contact is 200 °C. Basing on the auger electron spectroscopy and X‐ray diffraction results, the formation of Pd‐In intermetallic compound at the interface may be the reason for the increase of barrier height upon annealing at 200 °C. The formation of phosphide phases at the Pd/V/n‐InP interface could be the reason for the degradation in the barrier heights after annealing at 300, 400 and 500 °C. From the AFM results, it is evident that the overall surface morphology of the Pd/V Schottky contacts is fairly smooth. Copyright © 2011 John Wiley & Sons, Ltd.     

ChemInform Abstract: Synthesis,Structure, and Electronic Structure of CsAgGa2Se4.

The new title compound is prepared from a mixture of AgGaSe₂ (obtained from the elements at 900 °C, 2 d) and CsI in the molar ratio 1:2 (silica tube, Ar, 800 °C, 48 h).     

Spectrofluorimetric Determination of Gallium with 5-Bromosalicylidene-o-Aminophenol

Abstract

A method for the determination of trace amounts of gallium has been developed, based on the formation of a fluorescent complex between Ga (III) and 5-Bromosalicylidene-o-aminophenol (5-BrSOAPh). With excitation at 425 nm the chelate has an emission maximum at 520 nm. The reaction is carried out at apparent pH (pH?) 5.40 in an aqueous-ethanol medium (60% V/V ethanol). The influence of the reaction variables is discussed.     

电感耦合等离子体光谱法测定高纯镓中的痕量元素

比较了乙醚和甲基异丁基酮（MIBK）两种萃取剂对高纯镓中基体与杂质的分离效果。选择MIBK作为萃取剂,将高纯镓中的基体元素镓萃入有机相,绝大多数金属杂质则留在水相中,用电感耦合等离子体发射光谱法测定了水溶液中 的14种痕量元素。方法的加标回收率为805－110％,检出限在0.001-0.075ug/mL之间。