Improved Carrier Mobility of Thin Ge Films on Insulator by Solid-Phase Crystallization Combined with Interface-Modulation

High-carrier-mobility thin (≤ ~50 nm) films on insulator are needed to realize high-performance fully-depleted transistors. To achieve this, an advanced solid-phase crystallization technique of Sn-doped Ge (GeSn) on insulator has been developed. By introduction of a-Si under-layers between GeSn/substrate interfaces, energy barrier for carriers at grain-boundaries in grown films is significantly decreased. As a result, thin (~50 nm) poly-GeSn films with high carrier mobility of ~300 cm2/Vs are obtained by using a-Si under-layers. This mobility is the highest among ever reported data for Ge and GeSn thin-films (≤50 nm) on insulator grown at low-temperatures (≤500°C).