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

我们在1986年建立的利用低温沉积缓冲层在蓝宝石上生长III族氮化物的高产技术虽然带来了明亮的蓝、绿发光二极管和紫色激光二极管，但仍然存在高密度线错的问题。为了减少III族氮化物薄膜中的螺纹位错，我们有意在生长过程中施加水平双轴应力，从而弯曲螺纹位错。通过形成沟槽结构施加有意应力，使生长面向c轴方向倾斜。位错周围自生应力场沿生长面产生感应力，使得纯螺型、纯边型和混合型位错几乎所有类型的位错都发生弯曲。该机制不仅适用于GaN，也适用于AlGaN。首次实现了低位错密度的AlGaN。在本研究中，我们还建立了地应力监测系统，通过该系统可以精确地确定裂缝形成的临界厚度。我们还首次发现了氮化物中杂质的硬化效应。

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.