Investigation on the effective mass of Ge1-xSnx alloys and the transferred-electron effect

The electron band structures of Ge1-xSnx alloys were calculated using the nonlocal empirical pseudopotential method. The electron and hole effective masses were extracted, and the mobility enhancement over Ge was comprehensively analyzed. For the direct gap Ge1-xSnx with high Sn compositions, only a small fraction of electrons occupy the Gamma valley with high mobility at room temperature. Hence, the negative differential mobility resulting from the transferred-electron effect may not be observed, and the electron mobility enhancement over Ge is only two-fold. Low temperature conditions may lead to the transferred-electron effect and a significantly enhanced electron mobility. (C) 2015 The Japan Society of Applied Physics