Optical characterization of Cd1−x−yBexZnySe mixed crystals

Abstract

A detailed optical characterization of a series of wurtzite-type Cd1−x−yBexZnySe mixed crystals grown by the modified high pressure Bridgman method has been carried out via photoluminescence (PL) and contactless electroreflectance (CER) in the temperature range of 15–300 K. Room temperature surface photovoltage spectroscopy has been used as a diagnostic technique for checking the surface condition of the sample. For the mechanically polished sample, the surface photovoltage spectrum at room temperature recorded a below band edge broad feature which is most likely related to the surface states induced by mechanical defect. This feature can be eliminated via mechanical polishing and followed by chemical etching, and hence, only the exciton line was observed for the damage-removed sample. Typical PL spectrum at low temperature consists of an exciton line, an edge emission due to recombination of shallow donor-acceptor pairs, and a broadband related to recombination through deep level defects. Various interband transitions, originating from the band edge and spin-orbit splitting critical points, of the samples have been observed in the CER spectra. Comparison of PL and CER data for the Cd1−x−yBexZnySe samples shows that for a low Zn and Be content the peak positions of the excitonic emission lines in the PL spectra correspond quite well to the transition energies of the A exciton from the CER data. For samples with higher Be and Zn contents, the results indicate that localization of excitons has taken place at low temperatures. The parameters that describe the temperature dependence of the transition energy and broadening parameter of the fundamental band edge exciton have been evaluated and discussed.