Optical band gaps, Eg, up to 0.5 eV higher than in single-crystal samples, are observed for chemically deposited films of CdSe and explained in terms of a quantum-size effect, whereby the electrons are localized in individual crystallites. The increase in Eg depends strongly on deposition temperature, with the greatest increase obtained at the lowest temperature. Annealing at temperatures above the deposition temperature causes a decrease in Eg; this decrease is stronger at higher annealing temperature. Structural studies of the as-deposited layers showed them to be composed of microcrystalline, cubic CdSe, and electron microscopy resolved them into individual crystallites of typically 4080-A diameter, depending on deposition temperature. This is the first example reported of a three-dimensional quantum-size effect in a film. © 1987 The American Physical Society

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We show that photo-induced current transients in semi-insulating GaAs are well fitted by a unique sum of exponentials including the anomalous case, in which one of the exponentials has a negative amplitude. This fitting procedure is proposed as a more reliable method to be used in obtaining the trap emission constant. We also present an analytic solution for the kinetic equations of carriers taking into account the background current and the carrier recapture processes, which have been neglected in the previous approaches. This solution contains a very simple and physically coherent explanation for the appearance of negative peaks in the spectra of photo-induced transient current spectroscopy.

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