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In this paper, the optical properties of Au-doped rhenium diselenide (ReSe2:Au) single crystals have been reported. The doping effects of the material were characterized by polarization-dependent transmittance, piezoreflectance (PzR), and photoreflectance (PR) measurements in the temperature range of 15–300 K. The indirect energy gap of ReSe2:Au shows a slight redshift with respect to the undoped sample. The low temperature PzR and PR spectra reveal an E1ex feature at E∥b polarization as well as two features, E2ex and E3ex, at E⊥b polarization. The angular dependence of the excitonic feature amplitudes agrees well with Malus’ law. In comparison with the undoped ReSe2, the excitonic transition energies remain practically unchanged, while the broadening parameter of the excitonic transition features slightly increases due to impurity scattering. In addition, the parameters that describe the temperature variations of the band-edge excitonic transitions were evaluated and discussed. [ABSTRACT FROM AUTHOR]

We present an optical characterization of a Bridgman-grown zinc-blende-type Zn0.81Be0.04Mg0.15Se mixed crystal in the near-band-edge interband transitions using temperature-dependent photoluminescence (PL), contactless electroreflectance (CER), and photoreflectance (PR) in the temperature range of 15–400 K. Typical PL spectrum at low temperature consists of an exciton line, an edge emission due to recombination of shallow donor-acceptor pairs, and a broad band related to recombination through deep level defects. Interband transitions, originating from the band edge and spin-orbital splitting critical points of the sample, have been observed in the CER/PR spectra. The peak positions of the excitonic emission lines in the PL spectra correspond quite well to the energies of the fundamental transitions determined from electromodulation data. The parameters that describe the temperature dependence of the fundamental and spin split-off band gaps, and the broadening function of the band edge exciton are evaluated and discussed. [ABSTRACT FROM AUTHOR]

In this study, the optical properties of niobium-doped rhenium disulphide (ReS2:Nb) single crystals have been reported. The doping effects of the material were characterized by polarization-dependent transmittance, photoluminescence (PL), and piezoreflectance (PzR) measurements in the temperature range of 10–300 K. The indirect energy gap of ReS2:Nb shows a slight redshift with respect to the undoped sample. The low temperature PL spectra reveal two near direct band-edge excitonic peaks as well as two additional prominent features at higher energy side. The results agree well with that of the PzR investigation of the sample. In comparison with the undoped ReS2, the excitonic transition energies remain practically unchanged, while the broadening parameter of the excitonic transition features slightly increases due to impurity scattering. In addition, the parameters that describe the temperature variations of the band-edge excitonic transitions were evaluated and discussed. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]