Exceptional Responsivity (>6 kA/W) and Dark Current (<70 fA) Tradeoff of n-Ga2O3/p-CuO Quasi-Heterojunction-Based Deep UV Photodetector

Abstract

Reduction of high dark current has been a challenge for high responsivity photodetector (PD). In this context, the present article demonstrates an ultralow dark current of Ga2O3-based deep ultraviolet (UV)-photodetectors (UV-PDs) with enhanced photoresponses by tailoring a p/n heterojunction. An n- Ga2O3/p-CuO quasi-heterostructure-based deep UV-PDs has been fabricated on a sapphire (0001) substrate using an inexpensive electrospraying technique. After Ga2O3 deposition, platinum (Pt) electrodes ( $\sim 50$ nm) are fabricated as a metal–semiconductor–metal (MSM) device using sputtering. The device exhibits a very low dark current in the order of few fA $(6.94\times 10^{-14}$ A) at 5 V because of the enhanced depletion width at p/n heterojunction and Pt/ Ga2O3 metal–semiconductor contacts, which provides a narrow path for free carriers to travel from one metal contact to other under dark condition. The depletion layers get thinner due to the absorption of UV-photons in the UV-illumination condition. Hence, the photogenerated carriers get a wider channel to get collected at Pt-electrodes. Thus, in addition to ultralow dark current, the device exhibits an extraordinary photodetection characteristics, such as a high responsivity ( $\sim 6.33 \times 10^{3} \mathrm{AW}^{-1}$ ), remarkable phototo-dark current ratio ( $\sim 2.99 \times 10^{6}$ ), very high detectivity ( $\sim 4.44 \times 10^{14} \mathrm{mHz}^{0.5} \mathrm{~W}^{-1}$ ), and exceptional external quantum efficiency of $\sim 3.1 \times 10^{6}$ % at 5 V.