Comparative studies of single-crystalline-like Ge thin film on inexpensive flexible metal substrates

Single-crystalline-like germanium thin films on flexible metallic substrates are being developed for III-V compound semiconductors and silicon. The germanium films were deposited via reel-to-reel radio-frequency magnetron sputtering on multi-layered templates fabricated by ion beam assisted deposition (IBAD) and on Ni-5%W metal foils, prepared by Rolling Assisted Biaxially-Textured Substrates (RABiTS) process. In both cases, the germanium thin films were epitaxially grown on biaxially-textured CeO₂ films. The Ge film on IBAD template was found to exhibit a better crystallographic texture quality compared to films fabricated on Ni-W substrate. Although a similar micro-scale roughness was observed in Ge on both types of substrates, the grain size of Ge thin film on Ni-W was found to be more than 30μm which is much larger than that on IBAD tape with grain size of hundreds of nanometers.