Exciton localization by magnetic polarons and alloy fluctuations in the diluted magnetic semiconductor Cd1-xMnxTe.

Abstract

Photoluminescence was measured on the diluted magnetic semiconductor alloys ${\mathrm{Cd}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Mn}}_{\mathit{x}}$Te with 0.1x0.35, at temperatures between 4.2 and 60 K. Detailed line-shape analysis of the exciton luminescence is carried out to show the temperature dependence of peak positions, integrated intensities, line broadening, and asymmetry of the spectral shape. The luminescence intensity of the so-called ${\mathit{L}}_{2}$ line grows abruptly at low temperatures, and is attributed to exciton localization caused either by exciton magnetic polarons (EMP's) or alloy potential fluctuations (APF's). Only the lowest possible laser-power excitation enables us to observe the effect caused by the former. The characteristic line shape, especially the asymmetry of the luminescence line, is discussed in accordance with a type of localization: EMP's or APF's. We have determined the binding energies of localization from EMP's and APF's, as a function of Mn alloy concentrations. The results are compared with existing theories. It is found that the EMP energy depends on the cube of the number of Mn isolated local spins, and EMP formation is barely realized at x>0.20, and most stable at 0.05x0.1. We found that the primary localization due to APF's is not necessary for EMP formation, but that the possibility of spin-fluctuation localization still remains.