QUANTUM-DIMENSIONAL PHOTOLUMINESCENCE IN THE p-CdTe/n-CdS HETEROSTRUCTURE WITH CdTe MICROCRYSTALS

A new mechanism for the formation of near-edge photoluminescence due to the presence of a thin polycrystalline CdTe layer in a p-CdTe/n-CdS film heterostructure has been studied. The possibility of detecting low-dimensional effects in microcrystals of the linear size being on the order of one micron is considered. The effect has been found that shows the appearance in the low-temperature photoluminescence spectra of CdTe microcrystals of a dominant narrow "superhot" emission band which is located in energy above the fundamental edge of the intrinsic absorption of the bulk material. A theoretical model is developed according to which an anomalous emission band arises as a result of optical transitions of electrons from near-surface levels of spatial quantization to states of the valence band. It is shown that additional illumination of the heterostructure from the side of the transparent substrate with light from the CdS intrinsic absorption spectral region leads to quenching of the anomalous short-wavelength emission band and simultaneous “ignition” of the CdTe exciton-polariton luminescence. This effect finds a natural explanation if we take into account the illumination-induced generation of additional charge carriers, which compensate for the positive charge of the microcrystal surface and the negative space charge of acceptors. In the future, studies of the luminescence spectra of p-CdTe/n-CdS film heterostructures with transparent ohmic contacts are of interest, first of all, from the applied point of view in order to create new film solar cells on their basis. Such studies should include a more thorough analysis of the dependences on the size of microcrystals, the thickness of the CdS and CdTe layers, the doping method, temperature, the spectral composition of illumination, and its intensity, as well. It is necessary to develop a method for the theoretical calculation of the spectrum of superhot radiation under conditions of near-surface quantum-well recombination of photoelectrons taking into account their Coulomb interaction with free photoholes, which can be considered rigorously only in the framework of many-particle problem.

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