不同质量GaN单晶衬底上AlGaN/GaN功率开关器件的电流崩塌机理研究

AlGaN/GaN based power devices are ideal electronic devices with high efficiency, high power and high frequencies, which have great application potential. Currently, one of the largest challenges is the current collapse, which may result from the traps induced by surface states and internal defects (mainly including dislocation and compensated impurity). The detailed mechanism of current collapse is still unclear now. The proposed project will fabricate the AlGaN/GaN power devices grown on GaN free-standing substrate with different quality and study the regulation mechanism of the dislocation density with a large range and dislocation type in current collapse. Furthermore, the influence of internal defects, surface states and their distributions on the current collapse under different measurement conditions, such as temperature, bias voltage and pulse condition will be systematically studied in the devices grown on high-quality GaN substrate with very low dislocation density of 10E4 cm＾-2. In addition, the correlation of the crystal microstructure and macroscopic electrical properties will be revealed to improve the understanding of current collapse. The project will distinguish the independent influenced law of dislocation, surface stats and compensated impurity on current collapse, and also study the influence of the interaction of these defects. By the association of theoretical simulation, the corresponding physical model will be constructed. The results of the project will contribute to the solution of current collapse and give great support for the development and commercialization of AlGaN/GaN power devices of our country.

AlGaN/GaN功率开关器件是一种理想的高效大功率高频电力电子器件，具有广阔的应用前景，目前面临的最大挑战之一是电流崩塌效应，表面态以及材料内部缺陷（包括位错和补偿杂质等）形成的电子陷阱都是可能的原因，具体的作用机理仍有待进一步研究。本项目拟采用不同质量的GaN单晶衬底生长制备AlGaN/GaN功率开关器件，深入分析大范围位错密度变化及类型对电流崩塌效应的调控机理。进一步研究低位错密度（10E4 cm＾-2）下材料内部缺陷、表面态及其分布对不同测试条件（温度、偏置电压、脉冲）下电流崩塌影响规律，并揭示晶体微观结构与宏观电学性质间的关联关系。探究位错、表面态、补偿杂质对电流崩塌效应的独立影响规律，以及三者相互作用对电流崩塌效应的影响机理。结合理论模拟，并建立相应物理模型，为解决电流崩塌这一难题并促进我国在AlGaN/GaN功率开关器件的产业化进程奠定基础。

AlGaN/GaN功率开关器件是一种理想的高效大功率高频电力电子器件，相较传统的Si基器件，可以有效降低能耗，符合国家节能减排的发展战略，具有广阔的应用前景和巨大的市场。然而电流崩塌效应一直是影响其推广的最大挑战之一，研究其发生机理对解决这一难题、推广此类器件的应用具有极其重要的意义。本项目采用不同位错密度和不同掺杂类型的GaN作为衬底外延生长器件结构，并研究位错对电流崩塌的影响。为解决器件间隔离漏电问题，本项目首先研究了B、F、N离子注入器件隔离，发现注入F离子器件隔离的热稳定性和工艺兼容性最好。并对介质层进行优化研究，实现LPCVD生长氮化硅的关态栅漏电比最大饱和输出电流低9个数量级的水平。通过上述器件工艺优化及其外延生长条件及补偿掺杂的调控，外延了不同位错密度和不同掺杂的GaN衬底上的AlGaN/GaN HEMT器件结构，研究了位错密度、表面态密度及其相互作用对电流崩塌效应的影响规律和影响机理。研究发现当位错密度由4×106 cm-2增加到5×108 cm-2时，表面态密度增加1-2倍。因此位错应该对表面态有贡献。而用来表征电流崩塌的动态电阻与静态电阻的比值，由位错密度为5×108 cm-2时的136倍，降低到位错密度为4×106 cm-2时的2倍，说明位错是引起电流崩塌的一个重要的因素。在极低位错密度下，所有器件的电流崩塌相近，但是氮化硅钝化后在测试条件下电流崩塌基本可以消除，说明此时电流崩塌主要来源于势垒层的表面态。另外无论对何种掺杂衬底，降低位错密度，都可以有效降低电流崩塌效应。本项目的实施阐明了位错和表面态对电流崩塌的影响规律，为进一步降低甚或消除电流崩塌效应提供了新的思路和方向，将有利于提高我国在GaN功率开关器件等领域的整体研制水平，为我国在GaN功率开关器件的研发及产业化奠定基础。