Using oxygen-plasma treatment to improve the photoresponse of Mg0.18Zn0.82O/p-Si heterojunction photodetectors

Oxygen-plasma treatment was carried out on Mg0.18Zn0.82O thin films, grown on Si substrates, and the effects of oxygen-plasma treatment on Mg0.18Zn0.82O/p-Si heterojunction photodetectors (HPDs) were studied. It was found that with increasing of oxygen-plasma treatment time, the leakage current of Mg0.18Zn0.82O/p-Si HPDs is reduced. As compared to without treatment, the leakage current of treated HPDs is drastically decreased by 180 times and the rectification ratio improved greatly from 94.1 to 32,500. All Mg0.18Zn0.82O/p-Si HPDs appear about the same visible responsivity, in contrast the ultraviolet (UV) responsivity increases with longer oxygen-plasma treatment time. The UV (320 nm) responsivity increases from 0.56 A/W to 4.21 A/W for the untreated and 50-min treated HPDs, respectively. However a reduced UV responsivity is observed for the 70-min-treated HPDs, attributing to the oxygen atoms saturate at 50-min treatment time. The extended treatment time (over 50 min) causes more plasma bombardment on the Mg0.18Zn0.82O surface, thus degrading the responsivity. Two issues leads to the reduced leakage current and enhanced UV responsivity. One is that the introduced oxygen atoms fill the oxygen vacancy, and hence suppress the oxygen-vacancy-related defects. Another issue is that the excess oxygen atoms build a stable MgO film on the Mg0.18Zn0.82O surface, effectively passivating the HPDs. (C) 2015 Elsevier B.V. All rights reserved.