Photoconductivity of CdS powders by microwave loss measurement

We have studied the room-temperature photophysics of variously doped CdS and Cd(Hg)S powders by the microwave photoconductivity technique. Accordingly, we infer that both Cu and Ag are effective hole traps, the rate of hole trapping being limiting for the first order decay of photoconductivity. In CdS:Cu, states 0.14 and 0.33 eV below the conduction band are important to the photophysics of the powders; these have been demonstrated to be associated with sulfide vacancies. The presence of a (neutral) donor state associated with mercury appears to be a useful working hypothesis in the interpretation of observations made on Cd(Hg)S powders. Combination of donor (Ga or Eu) and acceptor (Cu or Ag) dopants leads to formation of spectroscopically detectable charge-transfer complexes in the CdS lattice; the conduction band can be populated directly from the acceptor state of the complex on irradiation.