蓝宝石邻晶面衬底MBE生长GaN薄膜的瞬态光电导弛豫特性研究

在实验优化MBE工艺条件的基础上，采用蓝宝石(0001)邻晶面衬底制备出了具有较高质量的GaN薄膜.XRD分析表明邻晶面衬底生长的GaN薄膜晶体结构质量明显提高，AFM表征结果显示邻晶面生长的样品表面形貌显著改善.蓝宝石衬底GaN薄膜的瞬态光电导弛豫特性对比实验研究发现，常规衬底生长的GaN薄膜光电导弛豫特性出现双分子复合、单分子复合和弛豫振荡三个过程，持续时间分别为0.91，7.7和35.5ms；蓝宝石邻晶面衬底生长的GaN薄膜光电导弛豫过程主要是双分子复合和单分子复合过程，持续时间分别为0.78和14ms.理论分析表明MBE生长GaN薄膜的持续光电导效应主要起源于本生位错缺陷引发的深能级. 关键词： 邻晶面蓝宝石衬底 GaN薄膜 瞬态光电导 弛豫特性

Instantaneous relaxation of photoconductivity in GaN film grown on vicinal sapphire substrate by MBE

By optimizing the technique and conditions experimentally, we have grown GaN film on vicinal sapphire (0001) substrates by radio frequency plasma-assisted molecular beam epitaxy (MBE). It was found that the films grown on vicinal sapphire (001) substrates have better quality than that grown on conventional substrate, as shovn by XRD and AFM characterization. Through investigation of the instantaneous relaxation behaviors of photoconductivity in GaN films grown on vicinal and common sapphire substrates, three stages of carrier recombination in the conventional MBE GaN film were discovered. The stages consist of bimolecular, monomolecular and persistent recombination phases in which the relaxation times are 0.91, 7.7 and 35.5ms, respectively. In comparison, only bimolecular and monomolecular recombination processes of photo-generated carriers were found in the GaN film grown on vicinal sapphire (0001) substrate, the relaxation time was measured to be 0.78 and 14 ms, respectively. Theoretical considerations directly show that the persistent conductivity mainly originates from the native dislocation defects in GaN film grown by MBE.