Highly responsive and low-cost ultraviolet sensor based on ZnS/p-Si heterojunction grown by chemical bath deposition

Abstract

The chemical bath deposition method has been widely used to synthesize low-cost and large scalable UV light photodetectors. Herein, nanocrystalline ZnS thin films were deposited on p-Si substrates. The crystalline quality of the as-deposited ZnS thin films was studied using X-ray diffraction (XRD) and scanning transmission electron microscopy (STEM). It was found that ZnS films showed good crystallinity with the growth direction along the (111) planes of a cubic zinc blend structure, as confirmed by both XRD and STEM analysis. The crystallite size was calculated to be 2.49 nm which is very close to the Bohr radius. Optical measurements revealed a blue shift of 5 nm which indicates quantum confinement effects in the as-deposited ZnS films. Furthermore, the morphology and grain size of ZnS film was estimated from scanning electron microscopy (SEM). Photoluminescence (PL) measurements showed evidence of multiple emissions in the as-deposited ZnS films, indicating the presence of commonly known intrinsic defects, for instance, Zn and S vacancies. The fabricated heterojunction ZnS/p-Si yields a high sensitivity (1.98 ×104), fast response and high peak detectivity (4.29 × 1012). The device showed a good responsivity of (68.98 mA/W) without biasing towards the UV light (350 nm) regime. Moreover, the linear Dynamic Range of 85.92 dB and the External Quantum Efficiency (EQE) of 23.42 % was obtained that can be utilized for UV photodetectors applications.