Optical characterization of Zn 0.95-x Be x Mn 0.05 Se mixed crystals

A systematic study of a series of ${\text{Zn}}_{0.95\ensuremath{-}x}{\text{Be}}_{x}{\text{Mn}}_{0.05}\text{Se}$ mixed crystals with different Be content $(0.05\ensuremath{\le}X\ensuremath{\le}0.20)$ grown by the modified high-pressure Bridgman method were carried out by room-temperature surface photovoltage spectroscopy (SPS), temperature-dependent photoluminescence (PL), and contactless electroreflectance (CER). A typical PL spectrum at low temperature consists of free exciton line, an edge emission due to recombination of shallow donor-acceptor pairs, and the ${\text{Mn}}^{2+}$-related intraionic emission. The near band-edge transition energies determined by analyzing the CER and SPS spectra showed a blueshift with the increase in Be content. The peak positions of band-edge exciton features in the PL spectra shifted slightly toward lower energies as compared to the corresponding transition energies obtained from CER and SPS data. The observed increases in the CER-PL shift with the increasing of Be content are explained by the increasing compositional disorder causing the smearing of the band-edge energies. The excitonic line broadening for the samples with larger Be/Zn ratio are attributed in part to the alloy-scattering effects and also to the poorer crystalline quality of the samples with higher content of Be. In addition, the parameters that describe the temperature dependence of the transition energies and broadening parameters of the band-edge excitonic transitions were evaluated and discussed.