S. Łęgowski

Temperature-dependent photoluminescence characterization of Cd1−x−yBexZnySe mixed crystals

Temperature-dependent photoluminescence (PL) characterization of a series of wurtzite-type Cd1−x−yBexZnySe mixed crystals has been carried out in the temperature range between 15 and 300 K. The samples were grown by the modified high pressure Bridgman method. A 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. The peak positions of the excitonic emission line in the PL spectra correspond quite well to the transition energies of exciton A from previously reported electromodulation reflectance data (Liu et al 2005 J. Appl. Phys. 98 083519). The parameters that describe the temperature dependence of the transition energy and broadening parameter of the band-edge excitonic emission are evaluated and discussed.

Optical characterization of Cd1−x−yBexZnySe mixed crystals

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 interba...

Temperature dependence of the edge excitonic transitions of the wurtzite Cd1−x−yBexZnySe crystals

We report a detailed investigation of the temperature dependence of the edge excitonic transitions of three Bridgman-grown wurtzite-type Cd1−x−yBexZnySe-mixed crystals using contactless electroreflectance (CER) and photoreflectance (PR) in the temperature range of 15–400 K. X-ray investigations show that the samples with beryllium (Be) content up to x=0.1 are uniform in composition and exhibit a single wurtzite phase or a wurtzite as the main phase. The transition energies of the A,B, and C excitons of Cd1−x−yBexZnySe are determined via a line-shape fit to the CER and PR spectra. The parameters that describe the temperature dependence of the interband transition energies and the broadening function of the excitonic features are evaluated and discussed.

Photoluminescence and electromodulation spectroscopy characterization of a Zn0.81Be0.04Mg0.15Se mixed crystal

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 15–400K. 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...

Optical characterization of Zn0.96Be0.04Se and Zn0.93Mg0.07Se mixed crystals

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 ba...

Temperature dependence of energies and broadening parameters of near band edge interband excitonic transitions in wurtzite ZnCdMgSe

An optical characterization of two wurtzite ZnCdMgSe crystalline alloys grown by the modified high-pressure Bridgman method was carried out by temperature-dependent photoluminescence (PL) and contactless electroreflectance (CER) in the temperature range of 10–300 K and photoreflectance (PR) measurements between 300–400 K. Low temperature PL spectra of the investigated samples consisted of the excitonic line, the “edge-emission” due to radiative recombination of shallow donor-acceptor pairs and a broad band related to recombination through deep level defects. Three excitonic features, A, B, and C, in the vicinity of band edge were observed in the CER and PR spectra. The peak positions of band edge excitonic features in the PL spectra were shifted slightly toward lower energies as compared to the lowest corresponding transition energies of A exciton determined from CER and PR data. The increase in the CER-PL shift with the increasing of Mg content in the investigated crystals was explained by the rising of ...

Optical characterization of bulk Zn1−xBexTe crystals

This paper presents an optical characterization of three bulk sphalerite Zn1−xBexTe crystals grown by the modified high pressure Bridgman method. The study was conducted in the near-band-edge interband transition regime using low temperature photoluminescence (PL), temperature-dependent contactless electroreflectance (CER) and/or photoreflectance (PR) in the temperature range of 15–400 K, and surface photovoltage spectroscopy (SPS) at room temperature. PL spectra at low temperatures of the samples investigated consist of an excitonic line, a band due to recombination of free electrons with holes located at shallow acceptors and a broad band related to recombination through deeper level defects. The band-edge excitonic transitions have been observed in the CER/PR spectra. The fundamental transition energies E0 are determined via lineshape fits to the CER/PR spectra. The values of E0 at room temperature obtained from CER/PR spectra correspond well to that determined from SPS measurements, and the Be contents x of the samples are determined using a linear equation which describes the room temperature band gap dependence on composition for the Zn1−xBexTe alloy system. The parameters describing the temperature dependence of the band-edge excitonic transition energies are evaluated and discussed.

Temperature dependent electromodulation characterization of Zn1−x−yBexMgySe mixed crystals

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.