Ge/SiGe multiple quantum well fabrication by reduced-pressure chemical vapor deposition

In this paper we deposit structures comprising a stack of 10 periods made of 15-nm-Thick Ge multiple quantum wells (MQWs) enclosed in a 15-nm-Thick SiGe barrier on SiGe virtual substrates (VSs) featuring different Ge content in the 85%-100% range to investigate the influence of heteroepitaxial strain on SiGe and Ge growth. With increasing Ge concentration of the VS, the growth rate of SiGe in the MQWs increases. Si incorporation into the SiGe layer also becomes slightly higher. However, almost no influence of the growth rate is observed for Ge growth in the MQWs. We argue that increased tensile strain promotes the Si reaction at the surface. In the case of SiGe growth on Ge, we observe a smeared interface due to Ge segregation during the growth. Furthermore, we observe that the interface width increases with increasing Ge concentration of the VS. We attribute this observation to the increased segregation of Ge driven by increased strain energy accumulated in the SiGe layers. We also observe that the MQW layer "filters out" threading dislocations formed in the VS.