Preparation and characteristics study of CdS/macroporous silicon/c-Si double heterojunction photodetector by spray pyrolysis technique

In this paper, a thin film of undoped cadmium sulfide CdS was deposited on p-type macroporous silicon by spray pyrolysis technique. Porous silicon was synthesised by electrochemical etching at 30 mA/cm2 for 15 min. The optical and structural properties of polycrystalline CdS sprayed at substrate temperature of 350 and 450 °C were investigated by using atomic force microscopy AFM, x-ray diffraction XRD and UV-vis spectroscopy. Scanning electron microscopy and optical microscopy were performed to study the structure of the porous silicon. XRD results confirmed formation of crystalline hexagonal CdS with preferential orientation along (002) plane. The electrical and optoelectronic characteristics of CdS/PSi/c-Si junction were investigated. The current-voltage characteristics of CdS/PSi/c-Si heterojunctions showed rectification characteristics and the ideality factor was greater than unity. The values of on/off ratio were 146 and 426 at 6 V for photodetectors prepared at 350 and 450 °C, respectively. The spectral responsivity results revealed that the CdS/PSi/c-Si junction prepared at 350 °C has two peaks of response located at 455 and 814 nm, while the peaks of response of CdS/PSi/c-Si photodetector prepared at 450 °C were located at 455 and 840 nm. The specific detectivity and carrier lifetime of the heterojunctions have been measured.