A broadband self-powered UV photodetector of a β-Ga₂O₃/γ-CuI p-n junction

The symmetric Ti/Au bi-layer point electrodes have been successfully patterned on the β-Ga₂O₃ films which are prepared by metal-organic chemical vapor deposition (MOCVD) and the γ-CuI films which are prepared by spin-coating. The fabricated heterojunction has a large open circuit voltage (V_oc) of 0.69 V, desired for achieving self-powered operation of a photodetector. Irradiated by 254-nm ultraviolet (UV) light, when the bias voltage is -5 V, the dark current (I_dark) of the device is 0.47 pA, the photocurrent (I_photo) is -50.93 nA, and the photo-to-dark current ratio (I_photo/I_dark) reaches about 1.08×10⁵. The device has a stable and fast response speed in different wavelengths, the rise time (τ_r) and decay time (τ_d) are 0.762 s and 1.741 s under 254-nm UV light illumination, respectively. While the τ_r and τ_d are 10.709 s and 7.241 s under 365-nm UV light illumination, respectively. The time-dependent (I-t) response (photocurrent in the order of 10^-10 A) can be clearly distinguished at a small light intensity of 1 μW·cm^-2. The internal physical mechanism affecting the device performances is discussed by the band diagram and charge carrier transfer theory.