Low temperature photoluminescence spectra of InS single crystals

Cataloged from PDF version of article.Photoluminescence (PL) spectra of InS were investigated in the wavelength region 477.5–860 nm and in the temperature range 8.5–293 K. We observed three PL bands centered at 605 nm (A-band), 626 nm (B-band) and 820 nm (C-band). The A- and B-bands are due to radiative transitions from the donor level at 0.01 eV below the bottom of the conduction band to the valence band and from the donor level at 0.06 eV below the bottom of the conduction band to the acceptor level 0.12 eV above the top of the valence band, respectively. The proposed energy-level scheme allows us to interpret the recombination processes in InS single crystals. Copyright © 1997 Published by Elsevier Ltd

Optical properties of GaS crystals: Combined study of temperature- dependent band gap energy and oscillator parameters

Optical parameters of gallium sulfide (GaS) layered single crystals have been found through temperature-dependent transmission and room temperature reflection experiments in the wavelength range of 400-1100 nm. Experimental data demonstrates the coexistence of both optical indirect and direct transitions and the shift of the absorption edges toward lower energies by increasing temperature in the range of 10-300 K. Band gap at zero temperature, average phonon energy and electron phonon coupling parameter for indirect and direct band gap energies have been obtained from the analyses of temperature dependences of band gap energies. At high temperatures kT≫ 〈Eph〉, rates of band gap energy change have been found as 0.56 and 0.67 meV/K for Egi and Egd, respectively. Furthermore, the dispersion of refractive index has been discussed in terms of the Wemple–DiDomenico single effective oscillator model. The refractive index dispersion parameters, namely oscillator and dispersion energies, oscillator strength and zero-frequency refractive index, have been found to be 4.48 eV, 24.8 eV, 6.99×1013 m−2 and 2.56, respectively. The results of the present work will provide an important contribution to the research areas related to the characterization and optoelectronic device fabrication using GaS layered crystals

Trap levels in layered semiconductor Ga2SeS

Cataloged from PDF version of article.Trap levels in nominally undoped Ga2SeS layered crystals have been characterized by thermally stimulated current (TSC) measurements. During the measurements, current was allowed to flow along the c-axis of the crystals in the temperature range of 10-300 K. Two distinct TSC peaks were observed in the spectra, deconvolution of which yielded three peaks. The results are analyzed by curve fitting, peak shape and initial rise methods. They all seem to be in good agreement with each other. The activation energies of three trapping centers in Ga2SeS are found to be 72, 100 and 150 meV. The capture cross section of these traps are 6.7 x 10(-23), 1.8 x 10(-23) and 2.8 x 10(-22) cm(2) with concentrations of 1.3 x 10(12), 5.4 x 10(12) and 4.2 x 10(12) cm(-3), respectively. (C) 2004 Elsevier Ltd. All rights reserved

Temperature dependence of the Raman-active phonon frequencies in indium sulfide

Cataloged from PDF version of article.The temperature dependence of the Raman-active mode frequencies in indium sulfide was measured in the range from 10 to 300 K. The analysis of the temperature dependence of the A(g) intralayer optical modes show that Raman frequency shift results from the change of harmonic frequency with volume expansion and anharmonic coupling to phonons of other branches. The pure-temperature contribution (phonon-phonon coupling) is due to three- and four-phonon processes. (C) 1999 Elsevier Science Ltd. All rights reserved

Temperature dependence of the first-order Raman scattering in GaS layered crystals

Cataloged from PDF version of article.The temperature dependence (15-293 K) of the six Raman-active mode frequencies and linewidths in gallium sulfide has been measured in the frequency range from 15 to 380 cm(-1). We observed softening and broadening of the optical phonon lines with increasing temperature. Comparison between the experimental data and theories of the shift and broadening of the interlayer and intralayer phonon lines during the heating of the crystal showed that the experimental dependencies can be explained by the contributions from thermal expansion and lattice anharmonicity. The pure-temperature contribution (phonon-phonon coupling) is due to three- and four-phonon processes. (C) 2000 Elsevier Science Ltd. All rights reserved

Low temperature photoluminescence spectra of layered semiconductor TlGaS2

Cataloged from PDF version of article.Photoluminescence (PL) spectra of TlGaS2 layered single crystals were studied in the wavelength region 500-860 nm and in the temperature range 9.5-293 K. We observed a total of three PL bands centered at 568 nm (2.183 eV, A-band), 718 nm (1.727 eV, B-band) and 780 nm (1.590 eV, C-band) at various temperatures. We have also studied the variations of the A- and B-band intensities vs excitation laser density in the range from 7 × 10-2 to 9 W cm-2. The A- and B-bands were found to be due to radiative transitions from the deep donor levels located at 0.362 and 0.738 eV below the bottom of the conduction band to the shallow acceptor levels at 0.005 and 0.085 eV located above the top of the valence band, respectively. The proposed energy-level diagram permits us to interpret the recombination processes in TlGaS2 layered single crystals. © 1997 Elsevier Science Ltd

Donor-acceptor pair recombination in AgIn5S8 single crystals

Cataloged from PDF version of article.Photoluminescence (PL) spectra of AgIn5S8 single crystals were investigated in the 1.44-1.91 eV energy region and in the 10-170 K temperature range. The PL band was observed to be centered at 1.65 eV at 10 K and an excitation intensity of 0.97 W cm(-2). The redshift of this band with increasing temperature and with decreasing excitation intensity was observed. To explain the observed PL behavior, we propose that the emission is due to radiative recombination of a donor-acceptor pair, with an electron occupying a donor level located at 0.06 eV below the conduction band, and a hole occupying an acceptor level located at 0.32 eV above the valence band. (C) 1999 American Institute of Physics

Thermally stimulated currents in layered Ga4SeS3 semiconductor

Cataloged from PDF version of article.Thermally stimulated current (TSC) measurements are carried out on nominally undoped Ga4SeS3 layered semiconductor samples with the cur-rent flowing along the c-axis in the temperature range of 10 to 150 K. The results are analyzed according to various methods, such as curve fitting, initial rise and Chen's methods, which seem to be in good agreement with each other. Experimental evidence is found for the presence of three trapping centers in Ga4SeS3 with activation energies of 70, 210 and 357 meV. The calculation yielded 7.9 x 10(-21), 7.0 x 10(-19) and 1.5 x 10(-13) cm(2) for the capture cross section, and 1.6 x 10(10), 6.5 x 10(10) and 1.2 x 10(11) cm(-3) for the concentration of the traps studied. (C) 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Resonant Raman scattering near the free-to-bound transition in undoped p-GaSe

Raman spectra of GaSe layered crystal have been measured using a He-Ne laser and temperature tuning the free-to-bound gap in the range 10-290 K. Resonance enhancement of E’’(2) mode has been observed for both incident and scattered photon energies equal to the free-to-bound transition energy