Ga液滴在不同溶蚀时间下的形貌演变分析

Influence of Etching Time on Nanostructure Evolution of Ga-Droplets on GaAs Substrate

采用分子束外延技术在Ga As缓冲层上沉积Ga液滴,探究溶蚀时间对Ga液滴形貌的影响。实验中溶蚀阶段的衬底温度为340℃,沉积6单原子层Ga液滴,在无As环境下分别溶蚀5、10和12. 5 min,待达到溶蚀时间后打开As阀,快速晶化Ga液滴。实验发现在低温、低沉积量的情况下,在溶蚀阶段Ga液滴并没有表现出在高温条件下的熟化现象而是进行一种原位的扩散。随着溶蚀时间的增加,液滴形貌逐渐由环盘结构向孔洞结构转变,内环的生长也表现出各向异性,倾向于沿[110]方向生长。随着溶蚀时间的延长内环的生长将集中于[110]方向的一边上,其高度明显高于其余三边。[110]方向上内环的高度差随溶蚀时间的增加而增加,但增速变缓。本文分析了这些现象的原因,并提出了Ga液滴在溶蚀阶段形貌演变的模型。

The influence of the etching time on the nanostructures of the Ga-droplets,deposited on GaAs substrate in molecular beam epitaxy（MBE） reactor, was investigated with scanning tunneling microscope（STM）. The preliminary results show that the etching time had a major impact. To be specific, Ga droplets were deposited on c （4 × 4 ） GaAs surfaces before the rapid re-crystallization involving As-deposition. In the first 5 min of Ga-droplet etching,oval discs formed at the Ga-droplet sites due to in-situ diffusion at 340℃. From 5 to 10 min,the oval discs changed into bigger hollow-discs on top of etched pits, accompanied by an anisotropical growth of the inner edge with [ 110] as the preferential orientation; moreover,the average height in [ 110] was found to be the highest,indicating the preferential diffusion, accumulation and growth of Ga. From 10 to 12. 5 min, only the etched pits existed. Possible Ga-droplet etching mechanism was proposed.