The fabrication and detailed electrical properties of heterojunction diodes based on n-type ZnO and p-type Si were reported. The effect of interface modification by H2O2 treatment on the electrical properties of n-type ZnO/p-type Si diodes was investigated. The n-type ZnO/p-type Si diode without H2O2 treatment showed a poor rectifying behavior with an ideality factor (n) of 2.5 and high leakage, indicating that the interfacial ZnSixOy layer influenced the electronic conduction through the device. However, the n-type ZnO/p-type Si diode with H2O2 treatment showed a good rectifying behavior with n of 1.3 and low leakage. This is because the thin SiOx layer acts as a thermodynamically stable buffer layer to suppress interfacial reaction between ZnO and Si. In addition, the enhanced photo-responsivity can be interpreted by the device rectifying performance and interface passivation. (C) 2012 Elsevier B.V. All rights reserved.