Electronic Processes and Fluctuations in Optically Quenched CdS and CdSe Crystals

A detailed analysis is given of the electronic fluctuations in a “five‐level” photoconductor, the “levels” being the conduction band, valence band. electron traps, shallow hole traps, and quenching centers. Two recombination paths are open to the electrons, viz. via the deep traps and via the quenching centers. It is assumed that the former process prevails at the surface and the latter mainly in the bulk. As a consequence fluctuations arise from diffusion to the surfaces, in addition to the effects of the electronic transitions. The various effective diffusion constants and lifetimes are complex. The resulting spectra are evaluated with the Green's function method and reveal ω −2 ‐, ω −5/2 ‐, and ω −3/2 ‐contributions. It is shown that the ω −5/2 ‐term disappears if there is no quenching, and that it is highly unlikely for this spectral dependence to appear in a more simple model than analyzed here. Surface recombination enhances the feasibility of the ω −5/2 ‐spectrum. The results, in as far as they can be analytically pursued, are in reasonable agreement with the previously described experimental data [1].