Twin-mediated orientation engineering for high-mobility Ge thin film via laser crystallization

Abstract

High-crystallinity germanium (Ge) thin films are crucial for advanced electronic applications, particularly for monolithic three-dimensional (M3D) integration under strict thermal budget constraints. However, conventional solid-phase crystallization (SPC) typically yields low crystallinity and randomly oriented grains. In this study, Ge thin films with pronounced orientation toward (1 1 0) are achieved by optimizing the power of continuous-wave (CW) laser crystallization to 1.8 W. This orientation was accompanied by an increased density of {1 1 1}-related twin traces and stable directional growth along the scan direction, suggesting a twin-related contribution to the orientation evolution during laser crystallization. The optimized Ge thin films exhibit improved crystallinity and reduced tensile stress compared to those crystallized via SPC or under non-optimized laser conditions. Hall-effect measurements indicate that the (1 1 0)-oriented Ge thin films achieve a low carrier concentration (2.21 x 1016 cm-3) and a high mobility (552 cm2V-1s-1), comparing favorably with many previously reported Ge thin films. Notably, among Ge films with comparable grain sizes, the (1 1 0)-oriented Ge thin films show significantly improved crystallinity and electrical properties. This suggests that grain size is not the only factor influencing electrical behavior and that crystallographic orientation substantially contributes to the observed performance enhancement. These findings provide a practical foundation for laser-based orientation engineering of Ge electronic materials for M3D integrated device applications.