Insights into recombination channels in a CVT grown ZnSe single crystal

Native defects and unintentional contaminations during growth can strongly influence the optical properties of semiconductors and their applications. The tailoring of these optical properties requires a deep understanding of the role of defects and hence contributes to the improvement of the crystal quality of the epitaxially grown active layer in optoelectronic devices. In this work, a ZnSe single crystal grown by chemical vapour transport was deeply investigated by photoluminescence. The observed luminescence comprises four narrow radiative transitions in the near-band edge, due to free-to-bound recombination processes involving acceptor defects, and three deep defect-related transitions at lower energies, involving the localization of a charge carrier in the electrostatic field created by an electrical charge of the opposite sign with a higher binding energy. In the latter case, the thermal activation of non-radiative de-excitation channels results in the release of the less bound carrier, whose ionization energies are estimated to be in the range of 176–206 meV. For the radiative transition observed at 2.135 eV, the proposed model comprises a donor state and a deeper acceptor state likely related to a Zn vacancy. Although the crystal evidences a low doping level, the density of ionized defects is high enough to determine the dominant dispersion mechanism in the lattice.