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 Si0.2Ge0.8 barrier on SiGe virtual substrates (VSs) featuring different Ge content in the 85%–100% range to investigate the influence of heteroepitaxial strain on Si0.2Ge0.8 and Ge growth. With increasing Ge concentration of the VS, the growth rate of Si0.2Ge0.8 in the MQWs increases. Si incorporation into the Si0.2Ge0.8 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 Si0.2Ge0.8 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 Si0.2Ge0.8 layers. We also observe that the MQW layer "filters out" threading dislocations formed in the VS.