Nanocrystalline and polycrystalline β-Ga₂O₃ thin films for deep ultraviolet detectors

The wide band gap and high breakdown field of β-Ga₂O₃ single crystals and thin films have recently attracted considerable attention not only for high-power applications, fabricating devices such as transistors and diodes, but also for several other applications such as deep-UV (DUV) sensors, with a cutoff at ∼280 nm, resulting in visible-blind detectors. Currently, most of the UV- and DUV-based simple metal−semiconductor− metal (MSM) systems use interdigitated electrodes, which requires high-quality, defect-free films. β-Ga₂O₃ films deposited by simple methods such as magnetron sputtering are scarce, and most high-quality β-Ga₂O₃ thin films have been demonstrated using pulsed laser deposition (PLD) and molecular beam epitaxy (MBE). Herein, we show a comprehensive study to effectively control the structural, optical, and electrical properties of β-Ga₂O₃ thin films deposited by sputtering. Highly oriented polycrystalline or nanocrystalline n-type β-Ga₂O₃ thin films were deposited by this method and evaluated as DUV detectors using a simple MSM structure under DUV light with 254 and 232 nm wavelengths. Different structures varying the number of fingers Are evaluated, under different light intensities and applying different electric fields. High responsivities are obtained, especially for nanocrystalline β-Ga₂O₃ thin films. The high responsivity for both films is attributed to self-trapped holes resulting in an internal gain. Higher responsivity is also observed for higher electric fields, lower light intensities, and a smaller number of fingers. Rise and decay times are comparable, in the range of 11−13 and 14−15 ms, respectively. Our results indicate that sputtered β-Ga₂O₃ thin films are promising for visible-blind DUV detectors. The paper also demonstrates simple strategies to control the crystallinity of sputtered β-Ga₂O₃ thin films.