Record-High Hole Mobility Germanium on Flexible Plastic with Controlled Interfacial Reaction
Toshifumi Imajo, Takamitsu Ishiyama, Noriyuki Saitoh, Noriko Yoshizawa, Takashi Suemasu, Kaoru Toko
Abstract
A semiconductor thin film with high carrier mobility was fabricated on a flexible film. During the solid-phase crystallization process of the densified amorphous Ge layer, the interfacial reaction with the GeOx underlayer is controlled by the GeOx thickness (0–300 nm) and the growth temperature (375–450 °C). The appropriate amount of oxygen diffusion from GeOx to Ge produces large Ge grains (up to 13 μm in diameter) with high crystal quality. The use of a high heat-resistant polyimide film allows postannealing at 500 °C and improves the hole mobility of Ge to 690 cm2 V–1 s–1 while maintaining flexibility. This hole mobility is higher than that of any other semiconductor thin films directly formed on insulators, including single-crystal Ge grown at high temperatures, and even higher than that of a Si wafer. The findings open up the possibility of incorporating high-speed transistors on flexible devices that surpass Si metal–oxide–semiconductor field-effect transistors.