Improved Carrier Mobility of Poly-Ge Ultrathin Films on Insulator by Solid-Phase Crystallization Combined with a-Si Capping Layers

Abstract

To improve the carrier mobility of poly-Ge ultrathin films (thickness: ~20 nm) on insulating substrates, a novel solid-phase crystallization (SPC) technique is developed. Carrier mobility of poly-Ge films obtained by conventional SPC of a-Ge films on insulator significantly decreases with decreasing thickness and cannot be measured for ultrathin films (thickness: ~20 nm). This phenomenon is attribute to retardation of SPC due to introduction of air into the surface regions of a-Ge films. To solve this problem, capping of the a-Ge films is examined. Interestingly, by introducing a-Si capping layers, carrier mobility is increased. As a result, high carrier mobility of ~80 cm2/Vs is obtained even for ultrathin films (thickness: ~20 nm). This technique will be useful to realize advanced thin-film devices for next-generation electronics.