p型GaN单晶衬底的HVPE制备及生长物理研究

The p-type GaN bulk substrate is not only favorable for the realization of LED structure with polarization electrical field and applied electrical field in the opposite direction, which contribute to improving internal quantum efficiency and resolving the critical problem of decrease of luminescent efficiency, but also helpful for the development of normally-off HEMT and MISFET. At the same time, it can be used as p-type conductive layer for ZnO-based semiconductor device. Therefore, it has great prospective future. However, the lack of p-GaN substrate with high quality, smooth surface and low resistivity prevents the development of above mentioned devices. The proposed project will fabricate p-GaN free-standing substrates by hydride vapor phase epitaxy (HVPE). For this purpose, the HVPE system will be improved and Mg will be used as dopant. The project will study the thermodynamic and kinetic of p-GaN growth and the influence mechanism of acceptor on strain and defects. As a result, the p-GaN free-standing substrate with thickness of 200 μm, the hole density of （1～5）E17/cm^3 and the FWMH of XRD less than 100 arcsec will be realized. Furthermore, the project will also study the luminescent mechanism of deep levels induced by acceptors. The new method of element co-doping will be explored to improve the electrical properties of p-GaN. The results of the project will provide material support for development of wide-band-gap semiconductor based optoelectronic and microelectronic devices of our country.

p型GaN单晶衬底，不仅能实现极化电场与外加电场反向的LED器件结构，有利于提升内量子效率并缓解发光效率下降这一关键难题，还有助于常关型HEMT器件及MISFET器件的研制，同时可为ZnO器件提供p型导电支撑，具有重要的研究意义。然而，由于缺乏晶体质量高、表面形貌平整、电阻率较低的p型GaN单晶衬底，严重限制了上述研究的发展。本项目拟采用氢化物气相外延（HVPE）法制备p型GaN单晶衬底。针对现有HVPE设备进行改进，以镁为掺杂元素，深入研究p型GaN材料生长的热力学及动力学效应，系统研究受主杂质对应力、缺陷的影响机理，获得厚度达200微米，空穴浓度达（1～5）E17/cm^3，X射线衍射半高宽小于100弧秒的p型GaN单晶衬底。本项目将进一步研究p-GaN中受主导致的深能级发光机理，探索元素共掺杂提升p型GaN电学性质的新途径。为我国宽禁带半导体光电子和微电子器件的发展提供材料支撑！

目前的光电子器件一般采用Ga极性外延生长，p型GaN层在有源区上。这种结构产生的内建电场和极化电场会导致量子限制斯塔克效应和器件发光效率的下降。p型GaN单晶衬底可以有效解决这个问题。MOCVD的生长方法生长速率慢，难以制备p型GaN单晶衬底，而HVPE方法则具有设备简单、成本低、生长速率快等优势，是制备P型GaN单晶衬底的良好技术手段。本项目通过改进 HVPE 设备的进气和导气结构以提高掺杂均匀性，通过调整生长温度、生长压力、各路源气体的流速及浓度以调控掺杂浓度。最后，结合表面热退火、表面活化剂等动力学调控手段，实现了 p 型 GaN 材料的高速度生长（大于 50 微米/小时），制备出厚度为500um，Mg掺杂浓度为1.3e19cm-3，X射线衍射半高宽小于100弧秒的高质量p型GaN单晶衬底。p型GaN单晶衬底的成功制备不仅有利于光电子器件发光效率的提升，同时有利于常关型HEMT器件的制备，具有重要的研究意义与广阔的应用前景。