极化调控GaN基三元合金能带和掺杂效应的研究

The further improvement of the performance of GaN based optoelectronic devices depends on optimization of the crystal quality, structure design, polarization effect and p-type doping and so on. Polarization-doping provides an attractive solution to p-type doping problem by ionizing acceptor dopants using the built-in electronic polarization. Further, the polarization electric field can modify the energy band of GaN based ternary alloys, which is expected to improve band bending, consequently enhancing the wave function overlap of the hole and electron . Based on our previous work of the polarization effect of III-V nitride semiconductors, we will use the polarization field to modify the energy band and doping effect of GaN based ternary alloy by using the metal organic chemical vapor deposition method and theoretical calculation in this research. We will investigate the formation mechanism and the scatter mechanism of holes in polarization-controled GaN based ternary alloys; analyse the relationship between the electrical properties and the polarization effect of the materials, study the mechanism of polarization electric field on the band. Then the polarization-modified energy band and doping effect of GaN based ternary alloys with high crystal quality and good performance will be achieved. Based on the above research, we will prepare high efficiency GaN based light-emitting diodes with improved efficiency droop effect by using the polarization-doped graded AlGaN replacing the conventional AlGaN as electron blocking layer and using the polarization-modified graded InGaN as quantum well to enhance the wave function overlap of the hole and electron.

GaN基光电器件性能的继续提高依赖于晶体质量、结构设计、极化效应以及p型掺杂等各方面的不断优化，借助III族氮化物中的极化电场所产生的高浓度感应电荷进行极化掺杂，同时利用极化电场进行能带调控，将有利于改善p型掺杂中高受主电离能所导致的低p型电导问题和强极化电场所致的空间电荷分离问题，从而进一步促进器件的发光效率。本项目拟通过理论能带模拟计算和金属有机物化学气相沉积等方法，探索极化调控的p型GaN基三元合金的空穴形成机理及散射机制；分析材料的电学性能与极化效应的变化规律以及极化电场对能带的作用机制；在此基础上发展出性能稳定的高p型电导高质量III族氮化物极化掺杂方法，获得能带和掺杂均极化调控的GaN基三元合金；采用极化调控的组分渐变AlGaN提高空穴注入效率，并采用组分渐变InGaN量子阱的极化电场调控能带，改善空间电荷分离现象，获得高效率低droop的GaN基发光二极管。

本项目组成员严格按照项目任务书中所述研究内容、研究方案及年度研究计划开展了相关研究，顺利完成了AlGaN及InGaN等GaN基三元合金的能带和极化掺杂研究。按照项目中的研究计划，本项目组依次开展了极化掺杂的AlGaN及InGaN三元合金的MOCVD外延生长研究，获得了高晶体质量的极化掺杂GaN基三元合金，并实现了极化电子和空穴浓度的可控。以此为基础，本项目组通过精确的理论计算，设计生长了具有确定极化诱导空穴浓度的组分渐变AlGaN外延层，使该极化诱导空穴充分补偿背景电子，实现高阻特性。该研究可用于GaN基高电子迁移率晶体管（HEMT）中的高阻缓冲层技术中。本项目组进一步利用极化掺杂理论，研究了GaN/InGaN量子阱的能带调控机理，改善了传统LED量子阱中由于极化电场导致的能带弯曲造成电子空穴空间分离的问题，有效提高了GaN/InGaN基蓝光LED的发光效率，在一定程度上缓解了发光效率的droop问题。最后，作为拓展工作，本项目组创新性的将极化掺杂技术应用于GaN基双异质结晶体管（HBT）的研究中，设计并生长了极化掺杂的p型基区，有效提高了基区导电率，为GaN基HBT的研究开拓了新思路。