Ultrasensitive Flexible κ-Phase GaO Solar-Blind Photodetector.

Flexible GaO photodetectors have attracted considerable interest owing to their potential use in the development of implantable, foldable, and wearable optoelectronics. In particular, β-phase GaO has been most widely investigated due to the highest thermodynamic stability. However, high-quality β-phase GaO relies on the ultrahigh crystallization temperature (usually ≥750 °C), beyond the thermal tolerance of most flexible substrates. In this work, we epitaxially grow a high-quality metastable κ-phase GaO (002) thin film on a flexible mica (001) substrate under 680 °C and develop a flexible κ-GaO thin film photodetector with ultrahigh performance. Epitaxial κ-GaO and the mica substrate are maintained to be thermally stable up to 750 °C, suggesting their potential for harsh environment applications. The responsivity, on/off ratio, detectivity, and external quantum efficiency of the fabricated photodetector are 703 A/W, 1.66 × 10, 4.08 × 10 Jones, and 3.49 × 10 %, respectively, for 250 nm incident light and a 20 V bias voltage. These values are record-high values reported to date for flexible GaO photodetectors. Furthermore, the flexible photodetector shows robust flexibility for bending radii of 1, 2, and 3 cm. More importantly, it shows strong mechanical stability against 10,000 bending test cycles. These results reveal the significance of high-quality κ-phase GaO grown heteroepitaxially on a flexible mica substrate, especially its potential for use in future flexible solar-blind detection systems.