Studies of low-energy optical absorption and gap state density of a-CdS by the constant photocurrent method

The absorption coefficient α of thin amorphous CdS films is investigated by constant photocurrent method. At energies below 1.6 eV a shoulder in the dependence α(E)is observed. This shoulder is considered in connection with electron transitions from localized states below the Fermi level to extended states of the conduction band. The parameters characterizing these states are calculated (N1 ≈︁ 1017 cm−3, E1= 1.03 to 1.12 eV, and W= 0.06 to 0.11 eV). It is assumed that the defects giving rise to the investigated localized states play the role of slow recombination centers.