Effects of UV-ozone treatment on the performance of deep-ultraviolet photodetectors based on ZnGa2O4 epilayers

Abstract

ZnGa2O4 epilayers have been grown on sapphire using the metalorganic chemical vapor deposition system. However, there is a trade-off between high conductivity and large defect density (oxygen vacancies) with the growth time of the growth of ZnGa2O4 epilayers. The ultraviolet (UV)-ozone treatment on the ZnGa2O4 epilayer at 100 ° C was proposed to reduce the number of oxygen vacancies in ZnGa2O4. The effect of UV-ozone treatment on the performance of ZnGa2O4 metal-semiconductor-metal (MSM) photodetector (PD) was evaluated. X-ray photoelectron spectroscopy analysis showed a decrease in the number of oxygen vacancies after UV-ozone treatment of ZnGa2O4. The measured lattice parameter near the surface around 10 nm of untreated ZnGa2O4 was 8.3434 ± 0.0120 A˙ and increased slightly to 8.3775 ± 0.0083 A˙ after UV-ozone treatment due to the decrease in oxygen vacancies. The dark current (at 5 V) of ZnGa2O4 PD was significantly reduced from 251 to 20.2 pA before and after UV-ozone treatment; it resulted in a substantial one-order enhancement in the on/off ratio of the PDs from 2.7 × 105 and 2.15 × 106 after the UV-ozone treatment. Furthermore, the rejection ratio also improved between 240 and 470 nm from 35 to 84 after UV-ozone treatment. The relationship between photocurrent and light intensity and the improvement in raising and falling time also showed the reduced density of trap states by UV-ozone treatment. This indicates that UV-ozone treatment can enhance the characteristics of ZnGa2O4 PDs for UV sensing applications.