Interfacial Nucleation Control in Amorphous GeSn Thin Films Using Bilayer Structure

Remarkable progress has been made in germanium-based thinfilm transistors in recent years. However, achieving both high field-effect mobility and a high on-off ratio is difficult because the crystallinity of polycrystalline Ge degrades as it becomes thinner. In this study, we investigated the interfacial nucleation control and grain size enlargement in the solid-phase crystallization of amorphous Ge thin films (<= 50 nm). A bilayer structure consisting of top nucleation and bottom nucleation suppression layers promoted nucleation at the surface rather than at the substrate interface, resulting in a significant enlargement of the grain size. In addition, Sn doping in Ge increased the grain size to 12 mu m, which was larger than that of most polycrystalline Ge thin films and contributed to the reduction in acceptor defects and improvement in hole mobility. The resulting hole mobility (260 cm2 V-1 s-1) and hole concentration (3 x 1017 cm-3) in the GeSn layer were among the highest for polycrystalline Ge-based thin films. These results will contribute to the realization of low temperature Ge-based thin-film transistors that could be superior to single-crystal Si transistors, leading to innovations in display devices.

Automated summary

Remarkable progress has been made in recent years in germanium-based thin film transistors. This study investigates the control of interfacial nucleation and grain size enlargement to improve the performance of polycrystalline Ge thin films. By using a bilayer structure and Sn doping in Ge, the grain size was significantly increased, resulting in high hole mobility and concentration. These findings have the potential to lead to the development of low temperature Ge-based thin-film transistors with superior performance compared to single-crystal Si transistors, leading to innovations in display devices.