Study of sub gap optical absorption parameters in Pb doped CdSe thin films

Abstract

Thin films of Pb doped CdSe have been prepared by thermal evaporation technique using inert gas condensation method. Constant photocurrent method is used to determine absorption coefficient in the low energy region. The absorption coefficient in the sub gap region follows an exponential Urbach tail. The value of Urbach energy increases after Pb doping in CdSe which indicates increase in structural disorder in the material. Energetic distribution of occupied density of states is calculated from sub gap absorption spectra using derivative procedure. The number density of defect states of thin films has also been calculated from Urbach energy.