热应力作用降低LPE层中的位错

提出由温差造成热剪切应力,引起衬底穿线位错滑移,形成<110>界面位错,从而降低LPE层中位错的模型。稳定自然对流下的温度梯度液相外延,存在衬底厚度方向的温差,能在边缘固定的衬底中造成热剪切应力。生长了厚GaAs和Ga_1-xAl_xAs层(x<0.3),估算的热剪切应力大于产生<110>暗线缺陷的临界剪切应力。表面腐蚀坑观察表明,外延层位错密度下降,或无位错。界面蚀槽和阴极荧光观察表明,衬底穿线位错在界面弯曲成<110>界面位错。透射电子显微镜观察表明,界面位错多关键词：

REDUCTION OF DISLOCATIONS IN LPE LAYERS DUE TO THE ACTION OF THERMAL STRESSES

We present here a model of the reduction of dislocations in LPB layers by the formation of <110> oriented interfacial dislocations parallel to the surface of the substrate due to the glide motion of substrate threading dislocations which is drived by the thermal stress produced by a temperature difference. In the temprature gradient LPE under a steady natural convection flow, there is a temperature difference across the thickness of the substrte. The temperature difference can cause a thermal shear stress in the fixed substrate. Thick GaAs and Ga_1-xAl_xAs (x<0.3) layers were grown on (100) GaAs substrates. The estimated value of the thermal stress is slightly greater than the critical resolved shear stress for the formation of <110> oriented dark line defects. The observation of subface etch pits shows that the epitaxial layers have lower dislocation densities than that of the substrates or are even dislocation-free. The observations of interfacial etch grooves and cathodoluminescence show that substrate threading dislocations bent so that segments run along the interface and a interfacial dislocation network is formed. The transmission electron microscopy observation shows that the majority of these interfacial dislocations are 60° type dislocations and the minority are Lomer dislocations. It implies that it is possible to eliminate all substrate threading dislocations with the introduction of interfacial dislocations by thermal shear stress.