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ABSTRACT: 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.
International Journal of Thermophysics 04/2012; 31(1):208-217. · 0.95 Impact Factor
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ABSTRACT: The concentration dependence of the thermal conductivity and thermal diffusivity were determined for Cd1-x
Mg
x
Se mixed crystals in the temperature range between 20◦C and 40◦C. To determine the thermal transport properties, the photopyroelectric setup in the back detection configuration was constructed.
In the concentration range 0<x<0.36, both thermal conductivity and thermal diffusivity were found to decrease with increasing magnesium concentration as
well as with increasing temperature. The observed concentration dependence is discussed in the framework of the Adachi model.
International Journal of Thermophysics 04/2012; 31(1):187-198. · 0.95 Impact Factor
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ABSTRACT: 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.
Journal of Physics Condensed Matter 05/2008; 20(25):255227. · 2.55 Impact Factor
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ABSTRACT: 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.
Journal of Applied Physics 01/2008; 103(1):013501-013501-6. · 2.17 Impact Factor
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ABSTRACT: Zn1-x-yBexMnySe solid solutions were grown from the melt by the high pressure Bridgman method. Optical, luminescence, photoelectric and photothermal properties of this material were investigated. Interpretation of the piezoelectrically detected photoacoustic spectra was performed using Jackson and Amer theory. From the spectral dependence of the amplitude and phase of photoacoustic signal as well as from photoluminescence spectra the variation of energy gap with composition was determined. The values of thermal diffusivity were derived from the dependence of photoacoustic signal on modulation frequency of the laser radiation illuminating the sample. The photoluminescence-excitation spectra and photoconductivity spectra were measured. The origin of luminescence in Zn1-x-yBexMnySe was discussed. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Crystal Research and Technology 11/2007; 42(12):1352 - 1358. · 0.95 Impact Factor
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ABSTRACT: We present an optical characterization of a Bridgman-grown wurtzite-type Cd0.85Mg0.15Se mixed crystal in the near-band-edge interband transitions using temperature-dependent contactless electroreflectance (CER) and photoreflectance (PR) in the temperature range 15–400 K. The interband excitonic transitions A and C originating from the band edge and spin–orbital splitting critical points of the sample, respectively, have been observed in the CER/PR spectra. The transition energies and broadening function of the excitonic features are determined via a lineshape fit to the CER/PR spectra. The parameters that describe the temperature dependence of the transition energies of excitons A and C, and the broadening function of exciton A, are evaluated and discussed.
Journal of Physics Condensed Matter 05/2007; 19(26):266002. · 2.55 Impact Factor
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ABSTRACT: 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.
Journal of Physics Condensed Matter 02/2007; 19(9):096216. · 2.55 Impact Factor
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ABSTRACT: Optical properties related to lattice vibrations of bulk Zn1-xBexSe, Zn1-x-yBexMnySe and Cd1-xBexSe alloys are reported. Optical phonons of the mixed crystals grown by the Bridgman method have been investigated by infrared spectroscopic ellipsometry in the wave-number range 300-8000 cm-1. The complex dielectric functions can be reproduced using a model with two or three classical damped oscillators corresponding to the BeSe-like transverse-optical phonon-modes and a Drude contribution from the free carriers. The frequencies of longitudinal-optical phonons have been found from the imaginary parts of the dielectric loss functions. The influence of the alloy composition on the zone-centre optical phonon frequencies is discussed. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Crystal Research and Technology 05/2006; 41(6):580 - 587. · 0.95 Impact Factor
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ABSTRACT: This paper presents the results of the studies of a thermal diffusivity of a series of mixed Zn1–xBexSe crystals by means of the piezoelectric technique. For determination of a thermal diffusivity of samples the method based on the measurement of the phase of the piezoelectric signal, in the rear configuration, as a function of a frequency of modulation was chosen. This method enabled analysis of the influence of Be concentration and the process of annealing of crystals on the values of their thermal diffusivities. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
physica status solidi (c) 03/2006; 3(4):746 - 749.
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ABSTRACT: The current-voltage, capacitance-voltage, and resistivity-voltage characteristics of metal-semiconductor-metal structures are studied. Experimental AuCdTeAu structures are made from n-type CdTe with carrier concentrations of 2.1 × 1020 m−3 and thicknesses of (12 ± 3) μm. A theoretical treatment is given of the current transport in the structures based upon the application of thermionic diffusion theory to double Schottky diodes. Good agreement is obtained between the experimental results and theoretical predictions.Die Strom-Spannungs-, Kapazität-Spannungs- und Widerstand-Spannungs-Kennlinien einer Metall-Halbleiter-Metall-Struktur werden untersucht. MSM-Strukturen werden aus n-CdTe mit einer Ladungsträgerkonzentration von 2,1 × 1020 m−3 und einer Dicke von (12 ± 3) μm hergestellt. Theoretisch wird der Stromtransport in den Strukturen auf der Basis der thermischen Diffusionstheorie für eine Doppel-Schottky-Diode berechnet. Die Messungen bestätigen gut die theoretischen Vorhersagen.
physica status solidi (a) 02/2006; 59(1):341 - 346. · 1.21 Impact Factor
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ABSTRACT: Cd1-xBexSe and Cd1-xMgxSe solid solutions were grown from the melt by the high pressure Bridgman method. Optical, luminescence and photothermal properties of these materials were investigated. Spectroscopic ellipsometry was applied for determination of the spectral dependence of the complex dielectric function (E) and refractive index n(E) at room temperature in the photon energy range 0.75-6.5 eV for samples with optic axis (c-axis) perpendicular to the air-sample interface. The critical point (CP) parameters for E0 and E1 transitions were determined using a standard excitonic CP function to fit the numerically calculated differential spectra ∂2ε2/∂E2. The dispersion of the refractive index of the alloys was modelled using a Sellmeier-type relation. The values of fundamental and exciton band-gap energies were estimated from the ellipsometric and photoluminescence measurements. The origin of luminescence in Cd1-xBexSe and Cd1-xMgxSe was discussed. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Crystal Research and Technology 03/2005; 40(4‐5):386 - 394. · 0.95 Impact Factor
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ABSTRACT: Photoelectric properties of Zn0.8Mg0.2Se mixed crystals grown by high pressure Bridgman method were investigated. Spectral distributions and temperature characteristics of photoconductivity as well as thermal and optical stimulation and quenching of luminescence and photoconductivity were measured. Relaxation of stored carriers were discussed in terms of random local potential fluctuation (RLPF) due to statistical fluctuations of composition. Based on the observed photoinduced phenomena in ZnxMg1−xSe, the potential applications of II–VI solid solutions for construction of optoelectronic devices were discussed. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
physica status solidi (c) 02/2004; 1(4):916 - 920.
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ABSTRACT: Optical and luminescence properties of Cd0.925Be0.075Se crystal grown by the modified Bridgman method are reported. Ellipsometric spectra were measured in the photon energy range 0.75–6.5 eV for a high symmetry orientation of the optic axis (c axis) being perpendicular to the air–substrate interface. The structure in the complex dielectric function was identified as E0(A), E0(C), E1(A), E1(B), E1(C), and E2 threshold energies. A large bowing of the main energy gap was estimated. Luminescence spectra were measured in the temperature range from 38 K to room temperature. Exciton emission at room temperature has a maximum at 1.873 eV. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
physica status solidi (c) 02/2004; 1(4):641 - 644.
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ABSTRACT: Optical properties related to lattice vibrations and photoluminecence of Zn1−xBexSe and Zn1−x−yBexMnySe alloys are presented. Optical phonons of the mixed crystals grown in a sphalerite phase for composition 0≤x≤0.35 and 0≤y≤0.22 have been investigated by IR spectroscopic ellipsometry in the wave number range 230–8000 cm−1. The complex dielectric functions can be reproduced using a model with three classical damped oscillators corresponding to the BeSe-like modes and a Drude contribution from the free carriers. The zone-centre optical-phonon frequencies increase continuously with increasing Be concentration. The amplitudes of the vibrations are also increasing with Be content.
Thin Solid Films · 1.89 Impact Factor
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ABSTRACT: Spectroscopic ellipsometry in the photon energy range from 0.04 eV to 6.50 eV is used for investigation of the optical response of Zn1-xBexTe crystals grown by a high-pressure Bridgman method in the composition range x ≤ 0.12. Infrared spectra display absorption bands centred between 411 cm−1 and 420 cm−1 associated with BeTe-type optical phonon modes. The positions of the transverse-optical and longitudinal-optical phonon modes have been found by modelling the line shape of the complex dielectric functions, ε˜ and Im(−ε˜−1), using a classical damped Lorentzian oscillator approach. Ellipsometric measurements in the VIS–UV range allow determination of the fundamental energy-gap (E0) and the higher threshold energies (E1, E1 + Δ1, E2) originating from the band edge and spin-orbit splitting critical points. We have found that the Be content x = 0.12 causes an increase of the fundamental energy gap about 0.15 eV at room temperature when compared to the E0 = 2.23 eV of ZnTe crystal at the same temperature. Photoluminescence spectra were measured in the temperature range from 30 K to room temperature. Luminescence at temperature T > 200 K is very weak. The peak positions of the exciton emission lines agree well with the E0 band-gaps derived from ellipsometric data if corrected for their temperature dependence.
Thin Solid Films 519(9):2795-2800. · 1.89 Impact Factor
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ABSTRACT: Zn1−xMgxSe crystals grown by the high-pressure Bridgman method for 0<x<0.38 were investigated. Composition of the samples was determined by electron microprobe analysis. Photoluminescence (PL) spectra were measured in the temperature range from 40 K up to room temperature. It was found that PL spectra measured at 40 K, consist of the exciton, edge and deep level emission bands. The broadening of PL bands due to compositional and structural disorder was observed. Auger electron spectroscopy (AES) together with argon ion sputtering was used to determine sub-surface composition of Zn1−xMgxSe crystals. AES depth profiles, obtained by ion milling of the samples and consecutive Auger analysis, allowed to obtain distribution of Zn, Mg and Se near the crystal surface.
Surface Science.
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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.
Surface Science. 603(1):131-137.
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ABSTRACT: A systematic study of a series of Zn0.95−xBexMn0.05Se mixed crystals with different Be content (0.05≤X≤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 Mn2+-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.
Phys. Rev. B. 79(23).
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ABSTRACT: The piezoelectric photothermal results obtained for a series of CdSe and Cd$_{1-x-y}$Be$_x$Zn$_y$Se mixed crystals are presented and discussed. The experimental results comprise the piezoelectric amplitude and phase spectra of these crystals. The thermal diffusivities were determined from the experimental piezoelectric phase spectra. The optical absorption spectra of the crystals were determined by the fitting of the piezoelectric amplitude spectra.
http://dx.doi.org/10.1051/jp4:2005125111.
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ABSTRACT: In this paper a series of experimental piezoelectric spectra of different Zn$_{1 - {\rm x} - {\rm y}}$Be$_{\rm x}$Mn$_{\rm y}$Se crystals are presented and discussed. Two groups of samples of these crystals exhibiting different composition with different surface treatment: grinded, polished and etched were prepared. The influence of a different surface treatment on piezoelectric amplitude spectra is presented and discussed in the model of an inactive layer.
http://dx.doi.org/10.1051/jp4:2006137071.
