Reduction of threading dislocations in group III nitride grown by vapor phase epitaxy and in-situ monitoring of the grown-in stress

我们于1986年建立的低温沉积缓冲层法在蓝宝石衬底上生长III族氮化物薄膜的高产率生长技术虽然带来了明亮的蓝、绿色发光二极管和紫色激光二极管，但仍然存在高密度的穿透位错问题，为了减少III族氮化物薄膜中的穿透位错，我们在生长过程中有意施加水平双轴应力，从而使穿透位错弯曲。通过形成沟槽结构施加有意应力，通过该沟槽结构，生长平面从c轴方向倾斜。位错周围的自感应力场在位错生长面上产生沿着方向的诱导力，从而使几乎所有类型的位错（包括纯螺型、纯刃型和混合型位错）发生弯曲。这一机制不仅适用于GaN，也适用于AlGaN，首次实现了低位错密度AlGaN，在本研究中，我们还建立了原位应力监测系统，通过该系统，我们可以精确地确定裂纹形成的临界厚度。我们还首次在氮化物中发现了杂质硬化效应。

Although high yield growth technology of group III nitrides on sapphire using low temperature deposited buffer layer which had been established by us in 1986 brought about the bright blue and green light emitting diodes and violet laser diodes, it still has the problem of high density threading dislocations.In order to reduce threading dislocations in the group III nitride films, we intentionally applied horizontal biaxial stress during growth, thereby bend the threading dislocations. Intentional stress was applied by forming trench structure, by which growth plane was inclined from the c-axis direction. Self induced stress field around dislocations causes inductive force along growth plane, thereby almost all types of dislocations including pure-screw, pure-edge, and mixed type dislocations are bent. This mechanism can be applied not only in case of GaN but also applicable to AlGaN.Low dislocation density AlGaN has been achieved for the first time.In this study, we also established the in-situ stress monitoring system, by which we can precisely determined the critical thickness for crack formation. We also found the impurity hardening effect in nitrides for the first time.