Enhanced UV Photodetector Efficiency with a ZnO/Ga$_2$O$_3$ Heterojunction

Heterostructures comprising uncoated ZnO and coated with thin layers of Ga$_2$O$_3$ were produced using spin-coating and subsequent hydrothermal processing. X-ray diffraction examination verifies the structural integrity of the synthesized heterostructures (HTs). Optical and photoluminescence spectra were recorded to assess the variation in absorption and emission of the Ga$_2$O$_3$-coated HTs in comparison to the pristine ZnO. We conducted comparative density-functional theory (DFT) computations to corroborate the measured band gaps of both categories of HTs. To assess the stability of our devices, the transient response to on/off light switching under zero bias has been studied. The rise time $\tau_{r1}$ ($\tau_{r2}$) is 2300 (500) ms and the decay time $\tau_{d1}$ ($\tau_{d2}$) is 2700 (5000) ms have been observed for bare ZnO and ZnO/Ga$_2$O$_3$ HTs, respectively. A significant amount of change was also observed in the electrical transport properties from bare ZnO to ZnO/Ga$_2$O$_3$. To see the performance of device, responsivity (R) and detectivity (D = 1/NEP$_B$) have been measured. It is evident from observation that responsivity of a device shows maximum value in UV region while it is reducing with visible region for HTs. In case of detectivity, the maximum value reached was $145 \times 10^{14}$ Hz$^{1/2}$/W (at ~ 200 nm) and $38 \times 10^{14}$ Hz$^{1/2}$/W (at 300 nm) for Ga$_2$O$_3$ coated ZnO, and bare ZnO HTs, respectively. The maximum responsivity measured for the bare ZnO HTs is 7 (A/W) while that of Ga$_2$O$_3$ coated ZnO HTs is 38 (A/W). It suggests a simple way of designing materials for fabricating broad-range cost-effective photodetectors.