Study of Deep Level Defect in Polycrystalline Cadmium Sulfide Films

Abstract

Photoluminescence (PL) spectroscopy is used to study the deep defect levels in CdS films grown by chemical bath deposition (CBD) and thermal evaporation (TE) techniques. The characteristics of PL bands and their evolution are studied mainly in three different types of (a) near stoichiometrically grown CBD (there after CBD-a), (b) off stoichiometrically grown CBD (there after CBD-b), and (c) near stoichiometrically grown TE samples to identify the origin of different defect levels in them. In general, TE filins present more distinct features in PL spectra than the CBD filins especially in the subband edge spectral region, indicating a lower concentration of defect states in them. A remarkable change in composition on thermal treatment (TT) of CBD-b [there after CBD-b (TT)] filins is observed along with the usual change in phase (cubic to hexagonal). It has been observed that the green emission (GE) band is more related to the crystalline phase of the films than to their chemical composition. The evolutions of other low energy emissions, e.g., so-called red emission (RE) and yellow emissions (YE) on temperature and film composition are studied.