Ultrasensitive Flexible\nκ‑Phase Ga₂O₃ Solar-Blind Photodetector

Abstract

Flexible Ga₂O₃ photodetectors have\nattracted\nconsiderable interest owing to their potential use in the development\nof implantable, foldable, and wearable optoelectronics. In particular,\nβ-phase Ga₂O₃ has been most widely investigated\ndue to the highest thermodynamic stability. However, high-quality\nβ-phase Ga₂O₃ relies on the ultrahigh\ncrystallization temperature (usually ≥750 °C), beyond\nthe thermal tolerance of most flexible substrates. In this work, we\nepitaxially grow a high-quality metastable κ-phase Ga₂O₃ (002) thin film on a flexible mica (001) substrate\nunder 680 °C and develop a flexible κ-Ga₂O₃ thin film photodetector with ultrahigh performance. Epitaxial\nκ-Ga₂O₃ and the mica substrate are maintained\nto be thermally stable up to 750 °C, suggesting their potential\nfor harsh environment applications. The responsivity, on/off ratio,\ndetectivity, and external quantum efficiency of the fabricated photodetector\nare 703 A/W, 1.66 × 10⁷, 4.08 × 10¹⁴ Jones, and 3.49 × 10⁵ %, respectively, for 250 nm\nincident light and a 20 V bias voltage. These values are record-high\nvalues reported to date for flexible Ga₂O₃ photodetectors.\nFurthermore, the flexible photodetector shows robust flexibility for\nbending radii of 1, 2, and 3 cm. More importantly, it shows strong\nmechanical stability against 10,000 bending test cycles. These results\nreveal the significance of high-quality κ-phase Ga₂O₃ grown heteroepitaxially on a flexible mica substrate,\nespecially its potential for use in future flexible solar-blind detection\nsystems.