RECOMBINATION MECHANISMS IN HIGHLY DOPED CDSIN

Time-resolved luminescence measurements of CdS:In crystals in the near -band-gap region are presented for a wide range of indium doping level s, i.e., for concentrations between 10(17) and 10(20) cm-3. Interactio ns of the indium dopants lead to a broad luminescence band near the ba nd-gap energy and alter the luminescence dynamics. A decrease of the l ifetimes of both donor and acceptor bound exciton complexes is observe d at medium doping levels (10(17)-10(18) CM-3 ). This is explained by the reduction of the effective binding energies leading to shorter dec ay constants of these complexes. The decay of the donor-acceptor-pair recombination luminescence is also investigated for indium concentrati ons below the Mott density. A statistical model proposed by Thomas and Hopfield is used to determine the electronically active impurity conc entration. At higher doping levels (up to 10(20) CM-3 the degeneracy o f the conduction band leads to a luminescence band attributed to radia tive non-k-conserving band-to-band transitions. The measured lifetimes reflect the number of occupied states in the conduction band and the number of free states in the valence band. A nonexponential fit reveal s the concentration of electronically active impurity centers. A corre lation between photogenerated and doping-generated carriers is establi shed for high excitation densities.