High-performance nanostructured p-Cu2S/n-Si photodetector prepared by chemical bath deposition technique

Abstract

In this study, we have fabricated and characterized high photosensitivity anisotype Cu2S/Si heterojunction photodetector by chemical bath deposition CBD technique without using a buffer layer or annealing. The effect of deposition time on the structural, optical and electrical properties of Cu2S film was studied. The optical data revealed that the optical energy gap was in the range of (2.65–2.8) eV depending on the deposition time. X-ray diffraction XRD data indicates the film deposited at 30 min was amorphous, while the films deposited at 50, 70 and 90 min were polycrystalline in nature with monoclinic chalcocite structure. Scanning electron microscopy SEM investigation confirms the formation of nanostructured Cu2S film with grain size ranged from 25 to 60 nm depending on the deposition time. Raman spectroscopy study shows two peaks located 265 and 474 cm−1 which assigned to the Cu–S bond vibration and to vibrational stretching mode, respectively. Hall measurement revealed that all the films are p-type and the film conductivity decreases as deposition time increase. The figure of merit of the films was calculated as a function of deposition time. Current–voltage characteristics of p-Cu2S/n-Si photodetectors under dark and illumination conditions were investigated. The responsivity of all photodetectors exhibits two peaks of response at 450 nm and 800 nm and the maximum responsivity was about 0.43 A/W at 450 nm and 0.58 A/W at 800 nm obtained for the photodetector prepared at 90 min. The figures of merit confirm that the deposition affecting the on/off ratio, specific detectivity and minority carrier lifetime of the photodetectors. The illuminated band diagram of p-Cu2S/n-Si photodetector was constructed.