Sn-Assisted Low-Temperature Growth and Crystallization of Ge Thin Films on Flexible Polyimide Substrates

Low-temperature fabrication of crystalline germanium (Ge) thin films on flexible substrates remains a critical challenge for flexible electronics. In this work, we demonstrate a tin (Sn)-assisted plasma-enhanced chemical vapor deposition approach for growing high-quality Ge thin films on flexible polyimide (PI) substrates at <240 °C. An ultrathin (∼1 nm) Sn layer promotes Ge nucleation and grain growth, resulting in improved crystallinity. Systematic optimization of deposition time, temperature, pressure, radio frequency (RF) power, and gaseous doping reveals an optimal growth window at 240 °C and 400 Pa, where Raman full width at half-maximum (FWHM) values as low as 14 cm–1 are achieved on PI. Phosphorus doping exhibits a strong synergistic effect with Sn catalysts, whereas excessive boron doping degrades crystallinity. Electrical measurements under bending, supported by simulations, reveal that resistance variation is strongly influenced by electrode configuration and strain distribution.