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We report a detailed investigation of the temperature dependence of the band-edge excitonic transitions of three Zn1-x-yBexMgySe mixed crystals using contactless electroreflectance (CER) and photoreflectance (PR) in the temperature range of 15–400 K. The samples were grown by the modified high pressure Bridgman methods. The fundamental transition energy E0 and broadening parameters are determined via a lineshape function fit to the CER and PR spectra. The parameters that describe the temperature dependence of the band-edge excitonic transition energy and broadening parameters are evaluated and discussed. [ABSTRACT FROM AUTHOR]

A detailed optical characterization of Zn0.96Be0.04Se and Zn0.93Mg0.07Se mixed crystal samples grown by the modified high-pressure Bridgman method has been carried out via photoluminescence (PL), contactless electroreflectance (CER), and photoreflectance (PR) in the temperature range of 15–400 K. With these optical diagnostic tools we observed features originating from exciton emission, an edge emission due to recombination of shallow donor-acceptor pairs (DAPs), and a broad band related to recombination through deep-level defects, as well as band-edge and spin-orbit splitting critical points interband transitions in CER and PR experiments. The optical properties of these two mixed crystals are compared. Our comparative study revealed that the beneficial effect of beryllium (Be) incorporation is superior to that of magnesium (Mg), in the sense that a Be-containing ternary alloy resulted in better crystalline quality with more intense excitonic emission line and weaker DAPs and deep-level defect-related bands. The peak positions of the excitonic emission lines in the PL spectra correspond quite well to the energies of the fundamental transitions obtained by means of electromodulation spectra. The parameters that describe the temperature dependence of the fundamental and spin split-off band gaps, and the broadening function of the band-edge excitons, are 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]

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]

Photoacoustic spectroscopy is a sensitive and useful method to investigate the quality of semiconducting A2B6 crystals. An imperfection of surface quality can strongly influence photoacoustic spectra but it shows the different character for the different kinds of semiconducting materials. To properly interpret the amplitude and phase spectra, the temperature distribution and its modifications, due to the surface defects, are needed. The Blonskij model of the temperature distribution was used to investigate the influence of the defect on the amplitude and phase spectra. [ABSTRACT FROM AUTHOR]

Piezoelectric photothermal spectroscopy has been used for measurements of the optical and thermal parameters of semiconductors. The investigated crystals were grown by the high-pressure Bridgman method under argon overpressure. The obtained photoacoustic (PA) spectra show the complexity of the effects observed for the different groups of selected A2B6 crystals. These effects comprise ideal samples and samples with damaged surfaces. The spectra show the influence of the surface treatment on the PA amplitude and phase spectra. [ABSTRACT FROM AUTHOR]

Abstract: We have performed a contactless electroreflectance (CER) study of the near band-edge interband transitions of a Bridgman-grown wurtzite-type Cd0.925Be0.075Se mixed crystal in the temperature range of 15–450K. The transition energies and broadening function of the excitonic features are determined via a lineshape fit to the CER spectra. The parameters that describe the temperature dependence of the transition energies of excitons A and C, and the broadening function of the exciton A are evaluated and discussed. [Copyright &y& Elsevier]

Abstract: This paper presents basics of the space selective piezoelectric photothermal spectroscopy method. This method is illustrated with the experimental piezoelectric amplitude and phase spectra of ZnBeMgSe(4%Be, and 15%Mg) samples and with the corresponding optical transmission spectra. The fitting of theoretical curves computed in the piezoelectric space sensitive spectroscopy method to experimental data indicated the presence of surface states located on both surfaces of the sample. From the fitting procedure the optical absorption coefficient spectra connected with the surface absorption on both sides of the sample were determined. [Copyright &y& Elsevier]