Structural and optical studies of ZnS nanocrystal films prepared by sulfosalicylic acid (C7H6O6S)-assisted galvanostatic deposition with subsequent annealing

Abstract

Zinc sulfide (ZnS) semiconductor nanocrystal films have been prepared on indium tin oxide coated glass substrates by sulfosalicylic acid (C7H6O6S)-assisted galvanostatic deposition with subsequent annealing. The deposition was performed at 10mAcm−2 in acidic electrolytes containing 15–30mM Zn(CH3COO)2, 20mM Na2S2O3, 200mM LiCl, 0.375mM Na2SO3, and 0 or 0.2mM C7H6O6S. Results show that the presence of C7H6O6S can suppress the precipitation of Zn and S impurity phases during the ZnS deposition process. As the [C7H6O6S]=0.2mM and [Zn2+]=20mM, the deposited ZnS film exhibits only hexagonal structure with an ideal Zn/S atomic ratio of 1.03 and a close-packed granular morphology. But its band gap about 2.86eV is narrower than the common value of ZnS, probably due to the existence of some spurious acetate species and defect states. By annealing the film at 400°C for 60min, its band gap increased up to 3.70eV, despite that its crystalline phase transformed into cubic structure which usually shows the narrower band gap than hexagonal ZnS. The significant band gap widening could be ascribed to the degradation of spurious acetate species and the reduction of various possible defect states in the annealing process.