Post deposition annealing: a route to bandgap tailoring of ZnSe thin films

Abstract

The ZnSe semiconductor thin films thermally evaporated on a glass substrate and an ITO substrate are studied and compared for their optical properties. Surprisingly, two different values of band gaps 2.49 and 2.91 eV in ZnSe thin films are observed, respectively deposited on glass substrate and ITO substrate. Similarly, the ZnSe films on ITO substrate has shown a hexagonal crystal structure with higher crystallinity as compared to that of ZnSe on glass. The ZnSe thin films deposited on glass substrate are also annealed at 350, 400, 450 and 500 °C under vacuum conditions, which has been resulted in improvement in crystallinity and increase in band gap energy from 2.45 to 2.54 eV. The ZnSe thin film deposited on ITO coated glass were annealed in vacuum and air at 450 °C. The air annealing has been resulted in a large increase in energy bandgap from 2.9 to 3.21 eV. It is also observed from these studies that the electrical conductivity of the films annealed in vacuum is higher than those of the annealed in air.