Photoluminescence and surface photovoltage spectroscopy characterization of Zn_(1-x-y)Be_xMg_ySe mixed crystals

摘要

This paper presents an optical characterization of three Bridgman-grown Zn_(1-x-y)Be_xMg_ySe mixed crystals in the near-band-edge interband transitions using temperature-dependent photoluminescence (PL) in the temperature range of 10-300 K and surface photovoltage spectroscopy (SPS) at room temperature. PL spectra at low temperatures of the investigated samples consist of an excitonic line, an edge emission due to radiative recombination of shallow donor-acceptor pairs, and a broad band related to recombination through deep level defects. The anomalous S-shape temperature dependence of the exciton emission peak for Zn_(1-x-y)Be_xMg_ySe crystals with high Mg content (y=0.26) can be explained as due to localization of excited carriers caused by statistical fluctuations of local composition. The peak positions of the excitonic emission lines in PL spectra correspond quite well to the energies of the fundamental transitions determined from SPS measurements. The parameters that describe the temperature dependence of the transition energy and broadening parameter of the band-edge excitonic emission are evaluated and discussed.