High-Performance Flexible Thin-Film Transistors Based on Single-Crystal-Like Germanium on Glass

Thin-film transistors (TFTs) grown on a flexible glass substrate using single-crystal-like germanium (Ge) channel to simultaneously achieve high carrier mobility, high performance characteristics, mechanical flexibility, and cost-effective large-area manufacturing are reported. High-crystalline-quality materials of biaxially textured CeO2 deposited at room temperature by ion-beam-assisted deposition followed by single-crystal-like Ge epitaxially grown at 550 °C by plasma-enhanced chemical vapor deposition on an amorphous substrate are developed. p-type Ge with {111} surface shows well-aligned grains in both out-of-plane and in-plane directions, as characterized by reflection high-energy electron diffraction, X-ray diffraction, and Raman spectroscopy. The material structures are fabricated to transistor devices with top-gate geometry. The devices (channel width and length = 80 and 14 μm) exhibit performance characteristics with on/off ratio of ≈106, a field-effect mobility of ≈105 cm2 V−1 s−1, and saturation current levels of ≈3.5 mA, which are significantly higher than performance metrics of other state-of-the-art TFTs based on amorphous Si, organic semiconductors, and semiconducting oxides. This development can open a new avenue for next-generation TFTs beyond the display applications.