AlGaN紫外探测器p电极的Ni/Au/Ni/Au欧姆接触结构研究

研究了AlGaN半导体p电极的Ni/Au/Ni/Au接触结构的性能和组织结构。退火 前,p电极接触具有明显的整流特性。经空气中550℃/3 min一 次退火和N2气氛中750℃/30 s二 次退火后,电极呈现出了良好的欧姆接触。采用扫描电镜(Scanning Electron Microscope, SEM)、透射 电镜(Transmission Electron Microscope, TEM)、能量分散谱仪(Energy Dispersive Spectrometer, EDS)和X射 线光电子能谱(X-ray Photoelectron Spectroscopy, XPS)观察了电极退火后金--半界面微结构的演化过程。结果表明,完全退火后的p电极 界面及金属层出现了明显的互扩散和界面反应现象;金--半界面上形成了存在良好共格/半共格关系的外延结 构。初始沉积的金属电极分层现象消失,形成了单一的电极结构。Ni向外扩散并与O发生反应,Au扩散至p-GaN 表面。在金-半接触界面上,Ga扩散至金属电极,造成界面附近的金属层中富集Au和Ga元素;Au和Ni明显扩散 至半导体表层,在金-半界面附近形成了Au、Ga和Ni富集现象。这些现象应该对于降低势垒高度和形成欧姆接触具有重要作 用。     

Performance assessment and sub-threshold analysis of gate material engineered AlGaN/GaN HEMT for enhanced carrier transport efficiency

The present work explores the features of gate material engineered (GME) AlGaN/GaN high electron mobility transistor (HEMT) for enhanced carrier transport efficiency (CTE) and suppressed short channel effects (SCEs) using 2-D sub-threshold analysis and device simulation. The model accurately predicts the channel potential, electric field and sub-threshold current for the conventional and GME HEMT, taking into account the effect of work function difference of the two metal gates. This is verified by comparing the model results with the ATLAS simulation results. Further, simulation study has been extended to reflect the wide range of benefits exhibited by GME HEMT for its on-state and analog performance. The simulation results demonstrate that the GME HEMT exhibits much higher on current, lower conductance and higher transconductance as compared to the conventional HEMT due to improved CTE and reduced SCEs. This in turn has a direct bearing on the device figure of merits (FOMs) such as intrinsic gain, device efficiency and early voltage. Tuning of GME HEMT in terms of the relative lengths of the two metal gates, their work function difference and barrier layer thickness has further been carried out to enhance the drive current, transconductance and the device FOMs illustrating the superior performance of GME HEMT for future high-performance high-speed switching, digital and analog applications.     

Scanning Ion Probe Studies of Silicon Implantation Profiles in AlGaN/GaN HEMT Heterostructures

This paper reports results of scanning ion probe studies of silicon implantation profiles in source and drain regions of AlGaN/GaN high-electron-mobility transistor (HEMT) heterostructures. It is shown that both the undoped channel length and the transition region between implanted and non- implanted regions become wider with increasing depth in the structure. These results may explain the previously reported existence of resistance associated with the transition region between implanted and non-implanted semiconductor regions in AlGaN/GaN HEMT heterostructures with non-alloyed Si-implanted source and drain ohmic contact regions.     

AlGaN/GaN界面特性研究进展

GaN是一种宽禁带半导体材料,由于具有优越的热稳定性和化学稳定性,使这种材料和与其相关的器件可以工作在高温和恶劣的环境中,并可用于大功率微波器件。本文主要介绍AlGaN/GaN有关界面特性,该特性反映了纵向纳米尺度下的能带特性;从AlGaN/GaNHEMT设计出发,给出了材料性质和结构参数对AlGaN/GaN异质结二维电子气特性影响的研究结果;讨论了AlGaN/GaN界面2DEG载流子的输运性质;分析了材料缺陷对AlGaN/GaN界面2DEG性质的影响;指出了有待研究的问题和方向。     

退火对高Al组分AlGaN P-I-N二极管光电性能的影响

研究了不同条件下的退火对高Al组分AlGaN P-I-N二极管性能的影响。研究结果表明，合适的退火条件既能使AlGaN与电极之间形成良好的欧姆接触，同时又能显著降低AlGaN P-I-N二极管的反向漏电流，反偏压5V时，暗电流密度由2.0×10-1A／cm2降为5.7×10-5A／cm2，串阻由18.01kΩ减小到1.071kΩ，从而优化了AlGaN P-I-N二极管的I-V特性。分析认为这与退火改善接触电极特性，同时消除器件制备工艺中引入的损伤、降低缺陷态密度有关。     

MOCVD生长不同Al组分AlGaN薄膜

本文研究了利用金属有机物化学汽相淀积系统(MOCVD)生长高质量不同Al组分AlxGa1-xN薄膜(0.13AlGaN层与GaN支撑层的应力，使AlGaN表面平整无裂纹，原子力显微镜(AFM)测量得到所有AlGaN薄膜粗糙度均小于1nm。通过原位干涉谱发现，AlGaN薄膜生长速率主要由Ga流量大小控制，随Al组分升高逐渐降低。利用X射线衍射和卢瑟福背散射(RBS)两种方法确定AlGaN薄膜的Al组分，发现Al组分与摩尔比TMAl/(TMGa+TMAl)关系为线性，说明在优化的生长条件下，Al原子与NH3的寄生反应得到了有效的抑制。     

High-temperature transport properties of 2DEG in AlGaN/GaN heterostructures

Transport properties of the two-dimensional electron gas (2DEG) in fully strained and partially strain-relaxed Al_0.22Ga_0.78N/GaN heterostructures at temperatures from 300 to 680 K have been investigated by Hall effect measurements. The 2DEG mobility was found to decrease rapidly with increasing temperature at the initial stage and then decrease slowly as temperature is further increased. Those features indicate strongly that the 2DEG mobility is primarily limited by LO phonon scattering processes at high temperatures. Meanwhile, the calculated results show that more electrons transfer to the higher-order sub-bands with increasing temperature, and hence the effect of screening on LO phonon scattering is weakened and the alloy scattering of the AlGaN layer on the 2DEG becomes stronger. Thus variation of 2DEG occupation in different sub-bands with increasing temperature also decreases mobility of the 2DEG.     

The effects of LT AlN buffer thickness on the properties of high Al composition AlGaN epilayers

To fabricate nitride-based ultraviolet optoelectronic devices, a deposition process for high-Al-composition AlGaN (Al content > 50%) films with reduced dislocation densities must be developed. This paper describes the growth of high-Al-composition AlGaN film on (0001) sapphire via a LT AlN nucleation layer by low pressure metalorganic chemical vapor deposition (LPMOCVD). The influence of the low temperature AlN buffer layer thickness on the high-Al-content AlGaN epilayer is investigated by triple-axis X-ray diffraction (TAXRD), scanning electron microscopy (SEM), and optical transmittance. The results show that the buffer thickness is a key parameter that affects the quality of the AlGaN epilayer. An appropriate thickness results in the best structural properties and surface morphology.     

Impact of Device Technology Processes on the Surface Properties and Biocompatibility of Group III Nitride Based Sensors

In this work we have investigated the impact of typical device processing steps on the surface properties (roughness, chemical composition, contact angle to water) of group III‐nitride based chemical sensors with emphasis on the electrical performance of the sensor and the biocompatibility. Basic sensing device is an AlGaN/GaN high electron mobility transistor. The widely distributed mammalian cell cultures HEK 293FT and CHO‐K1 served as biological model systems. The processing of the devices had only little influence on the cell growth onto the sensor. In all cases it was superior to silicon surfaces. Fluorine dry etching smoothes the surface and forms an oxide, which improves the electrical properties of the AlGaN/GaN sensor. In contrast, autoclave treatment enhances the carbon contamination with negative impact on the sensor properties and increased the contact angle to water. For all other treatments the contact angle recaptures a value of about 50 ± 5° after exposure to air or water droplets for some hours due to the contamination by hydrocarbons.     

Impact of strain relaxation of AlGaN barrier layer on the performance of high Al-content AlGaN/GaN HEMT

Owing to large direct bandgap energy, high saturation drift velocity, large conduction band discontinuities, high thermal stability and strong piezoelectric and spontaneous po- larization[1-4], AlGaN/GaN HEMTs have advantages over electronic devices based on Si, GaAs and their alloys in high-frequency, -temperature and -power applications. Many researches show[5,6] that the characteristics of AlGaN/GaN HEMTs depend on two-dimensional gas (2DEG) in heterostructures which has intimate r…