The Effect of annealing on structural, optical and electrical properties of ZnS/porous silicon composites

ZnS films were prepared by pulsed laser deposition (PLD) on porous silicon (PS) substrates. This paper investigates the effect of annealing temperature on the structural, morphological, optical and electrical properties of ZnS/PS composites by x-ray diffraction (XRD), scanning electron microscope (SEM), photoluminescence (PL) and I--V characteristics. It is found that the ZnS films deposited on PS substrates were grown in preferred orientation along β-ZnS (111) direction, and the intensity of diffraction peak increases with increasing annealing temperature, which is attributed to the grain growth and the enhancement of crystallinity of ZnS films. The smooth and uniform surface of the as-prepared ZnS/PS composite becomes rougher through annealing treatment, which is related to grain growth at the higher annealing temperature. With the increase of annealing temperature, the intensity of self-activated luminescence of ZnS increases, while the luminescence intensity of PS decreases, and a new green emission located around 550~nm appeared in the PL spectra of ZnS/PS composites which is ascribed to the defect-center luminescence of ZnS. The I--V characteristics of ZnS/PS heterojunctions exhibited rectifying behavior, and the forward current increases with increasing annealing temperature.