Preparation of ZnS-decorated MWCNTs/p-Si hybrid photodetector by pulsed laser deposition

Abstract

In the present work, a zinc sulfide (ZnS) nanostructure film is deposited on multi-walled carbon nanotubes (MWCNTs) by means of pulsed laser deposition technique. The structural, morphological, and optical properties of ZnS-decorated MWCNTs are investigated. X-ray diffraction (XRD) studies showed the presence of peaks related to polycrystalline faced-center cubic ZnS and MWCNTs. The best crystallinity is found for ZnS/MWCNTs nanocomposite prepared at 5.3 J/cm2. Scanning electron microscope (SEM) investigation shows that the deposited ZnS films have a smooth structure with some spherical particles attached to the film surface. The SEM image of the ZnS-decorated MWCNTs confirms the formation of a nanocomposite morphology structure. The optical energy gap of ZnS film decreases from 4 to 3.85 eV as laser fluence increases from 5.3 to 6.5 J/cm2, and in addition, the energy gap of ZnS-decorated MWCNTs nanocomposite film is smaller than that of ZnS film. The current-voltage characteristics of ZnS/Si and ZnS-decorated MWCNTs/Si heterojunction photodetectors are measured in dark and illumination conditions. The responsivity of n-ZnS/p-Si and n-ZnS/MWCNTs/p-Si prepared at 6.5 J/cm2 was found to be as high as 0.35 at 710 nm and 0.674 A/W at 610 nm, respectively. The figures of merit of the ZnS/Si photodetectors, including external quantum efficiency and specific detectivity, were improved after being embedded with MWCNTs. The band lineup of n-ZnS-decorated MWCNTs/p-Si under illumination was constructed.