Preparation of n-ZnO/p-Si heterojunction photodetector via rapid thermal oxidation technique: effect of oxidation time

Abstract

Isotype n-ZnO/p-Si heterojunction photodetectors were prepared by thermally deposited zinc film on the single-crystalline silicon substrate followed by rapid thermal oxidation (RTO) at 550 °C for different oxidation times (50, 100 and 150 s). The influence of oxidation time on the structural, optical, morphological, and electrical properties of prepared ZnO film was investigated. The experimental data showed that the oxidation time affecting the optical properties of ZnO films, the optical energy gap of ZnO film increased from 3.18 to 3.7 eV when the oxidation time increased from 50 to 150 s. X-ray diffraction XRD results revealed that the grown ZnO films are polycrystalline with hexagonal wurtzite structure. Preferred orientation along (101) plane was observed for ZnO film oxidized at 150 s. Scanning electron microscope (SEM) results confirmed that morphology and grain size of oxidized ZnO films were depended on the oxidation time. The current–voltage characteristics of ZnO/p-Si heterojunction photodetectors under dark and illuminated conditions have been studied as the function of oxidation time. The ideality factor of the heterojunction was calculated as the function of oxidation time. The responsivity, quantum efficiency, specific detectivity and rise time of the photodetectors were investigated. Increasing the oxidation time from 50 to 150 s resulted in increasing the responsivity of the photodetector from 220 to 300 mA/W at 750 nm.