First-principles calculation of alloy scattering and n -type mobility in strained Ge - Sn

We use first-principles electronic-structure theory to determine the intra- and intervalley electron-alloy scattering parameters in n-type Ge-Sn alloys. These parameters are used to determine the alloy scattering contributions to the n-type electron mobility of Ge-Sn at 300 and 15K using a first iteration of the Boltzmann transport equation in the relaxation-time approximation. For unstrained Ge-Sn, we find that an Sn concentration of at least 13.5% is needed to achieve an electron mobility greater than that of Ge. Our results show that the mobility of Ge-Sn can be over 25 times that of Ge, or 105cm2/(Vs). At 15K, incorporation of less than 6% Sn into Ge quadruples its mobility, which suggests that Ge-Sn has potential applications as a high-mobility 2D electron gas. Applying biaxial tensile strain to Ge-Sn further increases the mobility and achieves this improvement at lower Sn content than in unstrained Ge-Sn.