P-NiO/n-ZnO heterojunction photodiodes with an MgZnO/ZnO quantum well insertion layer

Abstract

P-NiO/n-ZnO heterojunction photodiodes (HPDs) with an MgxZn1-xO/ZnO quantum well (QW) insertion layer were fabricated by using a radio-frequency magnetron sputtering system. The mechanisms of QW on reducing leakage current and enhancing ultraviolet (UV)/visible rejection ratio of p-NiO/QW/n-ZnO HPDs were studied in detail. Compared with the HPDs without a QW, the leakage current is reduced by about 30 times in the HPDs with a QW, which enhances the rectification ratio from 10.6 to 90. The QW greatly suppresses the defect density by about 29.3 times and enhances the barrier height form 0.56–0.67 eV at p-NiO/n-ZnO interface. These issues largely decrease visible-response by a factor of 2241 and increase the UV (320 nm)/visible (500 nm) rejection ratio from 14 for the HPDs without a QW to 3070 for the HPDs with a QW, representing a factor of 220 improvement. Band-diagram shows the photo-generated electrons and holes from visible light are extracted to the outer circuit in the HPDs without a QW, contributing a large visible-response. In contrast, the visible-generated carriers are few in the HPDs with a QW due to less defect density and these carriers are effectively confined within the ZnO well layer because the QW introduces a large barrier height, which drastically reduces visible-response.