Thickness-dependent behavior of strain relaxation and Sn segregation of GeSn epilayer during rapid thermal annealing

The behavior of strain relaxation and Sn segregation of GeSn epilayers during growth and thermal annealing is very complex depending on the growth method, thickness and Sn content of the GeSn epilayer. Herein, we report on the thickness-dependent behavior of fully strained Ge1-xSnx epilayers (x = 0.097) on Ge (100) substrate grown by molecular beam epitaxy during rapid thermal annealing (RTA). It is found that when the GeSn epilayer is thinner than the critical thickness at Sn segregation temperature (hc(Ts)), GeSn epilayers would hardly be relaxed before Sn segregation during RTA. While for GeSn epilayer thicker than the hc(Ts), GeSn epilayers will undergo the process of strain relaxation before Sn segregation. The results indicate that the competition between Sn segregation and strain relaxation by generation of misfit dislocations strongly depends on the thickness of GeSn epilayers. A semi-quantitative model is proposed to explain the priority of Sn segregation or strain relaxation during RTA in terms of temperature-dependent critical thickness, which can be used to guide the design of strain-relaxed GeSn epilayer without Sn segregation for optoelectronic device application.