Enhanced Photoelectric Properties of n-ZnO NWs/p-Si Heterojunction LEDs by Inserting an Insulating MgO Layer Using Sol–Gel Method

ZnO nanowires (ZnO NWs) were synthesized by hydrothermal method on Si (100) substrates, in which an insulating MgO layer deposited using sol–gel method was inserted between the seed layer and Si substrate. The effects of MgO layer on the microstructure, luminescence and electrical properties of ZnO NWs as well as n-ZnO NWs/p-Si heterojunction LEDs were investigated. With the insertion of MgO layer, well-aligned ZnO NWs with good crystalline quality are obtained, which can be attributed to the smooth seed layer with homogeneous globular particles. The electroluminescence spectra of n-ZnO NWs/MgO/p-Si heterojunction LEDs exhibit a broad emission band from near ultraviolet to yellow-green region. n-ZnO NWs/MgO/p-Si heterojunction also shows an enhanced ultraviolet photoluminescence efficiency, and its defect-related visible emission is greatly suppressed compared with that of n-ZnO NWs/p-Si heterojunction. The current–voltage curves of both heterojunction LEDs present a typical rectifying behavior, but the rectification ratio increases almost 5 times by inserting MgO layer, which is ascribed to a reduction in the leakage current under reverse bias voltage.