Liu Nanliu, Jiang Yongjing, Xiao Jian, Liang Zhiwen, Wang Qi, Zhang Guoyi
School of Physics and Electronics, Qiannan Normal University for Nationalities, Duyun, China.
Dongguan Institute of Opto-Electronics, Peking University, Dongguan, China.
Front Chem. 2021 Apr 22;9:671720. doi: 10.3389/fchem.2021.671720. eCollection 2021.
Free-standing GaN substrates are urgently needed to fabricate high-power GaN-based devices. In this study, 2-inch free-standing GaN substrates with a thickness of ~250 μm were successfully fabricated on double-polished sapphire substrates, by taking advantage of a combined buffer layer using hydride vapor phase epitaxy (HVPE) and the laser lift-off technique. Such combined buffer layer intentionally introduced a thin AlN layer, using a mix of physical and chemical vapor deposition at a relatively low temperature, a 3-dimensional GaN interlayer grown under excess ambient H, and a coalescent GaN layer. It was found that the cracks in the epitaxial GaN layer could be effectively suppressed due to the large size and orderly orientation of the AlN nucleus caused by pre-annealing treatment. With the addition of a 3D GaN interlayer, the crystal quality of the GaN epitaxial films was further improved. The 250-μm thick GaN film showed an improved crystalline quality. The full width at half-maximums for GaN (002) and GaN (102), respectively dropped from 245 and 412 to 123 and 151 arcsec, relative to those without the 3D GaN interlayer. The underlying mechanisms for the improvement of crystal quality were assessed. This method may provide a practical route for fabricating free-standing GaN substrates at low cost with HVPE.
制造高功率氮化镓基器件迫切需要独立的氮化镓衬底。在本研究中，利用氢化物气相外延（HVPE）和激光剥离技术相结合的缓冲层，在双面抛光蓝宝石衬底上成功制备了厚度约为250μm的2英寸独立氮化镓衬底。这种组合缓冲层通过在相对较低温度下使用物理和化学气相沉积的混合方法有意引入了一层薄的氮化铝层、在过量的环境氢气下生长的三维氮化镓中间层以及一个合并的氮化镓层。研究发现，由于预退火处理导致氮化铝核尺寸大且取向有序，外延氮化镓层中的裂纹可以得到有效抑制。通过添加三维氮化镓中间层，氮化镓外延膜的晶体质量进一步提高。250μm厚的氮化镓膜显示出改善的晶体质量。相对于没有三维氮化镓中间层的情况，氮化镓（002）和氮化镓（102）的半高宽分别从245和412下降到123和151弧秒。评估了晶体质量改善的潜在机制。该方法可能为利用HVPE低成本制造独立氮化镓衬底提供一条实用途径。
