Substitutional Sulfur in CdSe: Localized Vibrational Modes

The substitutional sulfur at the selen site in wurtzite CdSe is identified by a combination of infrared absorption spectroscopy and first principles calculations. The dominant isotope gives rise to two local vibrational modes at 270.6 and 271.4 cm−1 (10 K) assigned to the nondegenerate and the twofold degenerate E representations of the point group. The corresponding signals of the isotope occur at 263.6 and 264.4 cm−1. The results of measurements performed on a set of samples supplied by different manufacturers highlight that sulfur is an ubiquitous impurity in CdSe unintentionally incorporated into the crystals during the process of growth.