Effect of oxygen on the properties of encapsulated polycrystalline CdSe films

This paper presents a comprehensive study of the effects of annealing silicon dioxide encapsulated CdSe films in oxygen on the microstructure, resistivity, photosensitivity and energy levels. The energy levels were investigated by using the independent methods of thermally stimulated current, photocurrent spectral response, and Hall measurements. The film structure is wurtzite with grains of average size 0.35 mu m, which extend through the thickness of the films. Annealing the films in oxygen at 450 degrees C increases the resistivity from 10 ohm cm to 10(6) ohm cm. The electron mobility, which has an activation energy of 0.08 eV, remains constant at about 100 cm(2) V-1 s(-1) during the anneal steps. The change in the resistivity is due to a combination of thermal rearrangement and oxygen diffusing uniformly into the films. Various energy levels ranging from 0.11 eV to 1.3 eV were detected and the density of all these decreased on annealing.