Solution-Processed-2D on 3D Heterojunction UV–Visible Photodetector for Low-Light Applications

We have demonstrated a heterojunction photodetector (PD) based on reduced graphene oxide (r-GO) and metal–organic chemical vapor deposition (MOCVD)-grown gallium nitride (GaN) that can sense very low light intensities in the above-band-gap and below-band-gap regimes, showing no and high photoconductive gains, respectively. The current–voltage characteristics of the device transforms from quasi photoconductive to photodiode behavior once the illumination wavelength is in the below-band-gap regime. The device exhibits a very low dark current of 0.85 pA at zero bias. In the self-powered mode with low-light conditions (∼0.38 μW/cm2) at 360 nm illumination, the light-to-dark current (ILight/IDark) ratio, responsivity (Rλ), specific detectivity (D*), and external quantum efficiency (EQE) of the fabricated PD were calculated to be ∼1 × 104, 0.22 A/W, 1.486 × 1014 Jones (cm Hz1/2 W–1), and 77%, respectively. The response and recovery time of the PD were typically 485 and 886 μs, respectively under 280 Hz light switching frequency at zero bias. The device also shows significant photoconductive response with a typical persistent photoconductivity behavior at an applied bias of 5 V with extremely large ILight/IDark ratio of ∼107 at 360 nm (∼0.15 mW/cm2). The Rλ, D*, and EQE were found to be 529 A/W, 4.25 × 1016 Jones, and ∼2 × 105 %, respectively, for 360 nm illumination under low-light conditions (∼0.38 μW/cm2), at 5 V applied bias. The extraordinary performance of the device in both photovoltaic and photoconductive modes makes r-GO/GaN heterojunction scheme suitable for dual-mode low-light UV–visible applications.