Low temperature growth of Ge1 − xSnx buffer layers for tensile–strained Ge layers

We have investigated the dependence of Sn precipitation and crystallinity of Ge1 − xSnx layers on the growth temperature. We also demonstrated a growth of a tensile–strained Ge layer on strain-relaxed Ge1 − xSnx buffer layers. In order to suppress Sn precipitation in Ge1 − xSnx layers and improve the crystalline quality, we strongly suggest that point defects have to be introduced by using low temperature growth MBE. The point defects effectively contribute to the lateral propagation of misfit dislocations at the Ge1 − xSnx/virtual Ge substrate. The point defects would be also effective to stabilize substitutional Sn atoms in Ge1 − xSnx layers due to the formation of Sn-vacancy pairs. As a result, Sn precipitation was suppressed in the Ge1 − xSnx layer by low temperature growth, and we realized the Ge1 − xSnx layer with a Sn content of 7.1%. We also achieved the formation of the Ge layer with a tensile–strain value of 0.71%.