Photoluminescence analysis of zinc(1-x) manganese(x) selenium

Zn1-x is a ternary alloy belonging to a class of materials known as Diluted Magnetic Semiconductors (DMS's). Single-crystal samples of this material possesses a cubic (zinc-blende) structure for x<0.30 and a hexagonal (wurtzite) structure for 0.30<x<0.57. Photoluminescence spectra are taken on the samples with x=0.00080, 0.0029, 0.0093, 0.017, 0.029 and 0.038 in the temperature range between 26 --> 300 K. Three emission bands are detected and are named the YEL (centered ~2.12 eV), ORA (centered 1.91 --> 1.98 eV) and IR bands. The shift of the YEL band is observed and related to the d-d interaction of the Mn^+2 ions and to thermal lattice expansion. The electron-phonon interaction is used to explain the broadening of the YEL band. A model is proposed to explain the existence of the ORA band and the shift of its energy with temperature and Mn concentration. This model for the first time provides a detailed explanation of the anomalous behavior of the energy gap of this material for low Mn concentrations.