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.

We study light-extraction efficiency (LEE) of AlGaN-based deep-ultraviolet light-emitting diodes (DUV-LEDs) using flip-chip (FC) devices with varied thickness in remaining sapphire substrate by experimental output power measurement and computational methods using 3-dimensional finite-difference time-domain (3D-FDTD) and Monte Carlo ray-tracing simulations. Light-output power of DUV-FCLEDs compared at a current of 20 mA increases with thicker sapphire, showing higher LEE for an LED with 250-μm-thick sapphire by ~39% than that with 100-μm-thick sapphire. In contrast, LEEs of visible FCLEDs show only marginal improvement with increasing sapphire thickness, that is, ~6% improvement for an LED with 250-μm-thick sapphire. 3D-FDTD simulation reveals a mechanism of enhanced light extraction with various sidewall roughness and thickness in sapphire substrates. Ray tracing simulation examines the light propagation behavior of DUV-FCLED structures. The enhanced output power and higher LEE strongly depends on the sidewall roughness of the sapphire substrate rather than thickness itself. The thickness starts playing a role only when the sapphire sidewalls become rough. The roughened surface of sapphire sidewall during chip-separation process is critical for TM-polarized photons from AlGaN quantum wells to escape in lateral directions before they are absorbed by p-GaN and Au-metal. Furthermore, the ray tracing results show a reasonably good agreement with the experimental result of the LEE.

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