BYCdInGaS4 single crystals are characterized by a layer structure. For the first time it was shown by Shand /1/ that this compound crystallizes in the CQV space group. 5In this note we give first results of polarized reflection and transmission measurements of CdInGaS4 in the reststrahlen region at room temperature. The single crystals of CdInGaS4 were grown by the Bridgman and the chemical transport reaction method from high-purity elements (at least 99.999%) in an evacuated quartz tube. The yellow coloured crystals grown by the two methods were plate-like and had one prominent cleavage plane perpendicular to the z-axis (which coincided with the optical axis).According to /2/ CdInGaS4 crystallizes in the Civ space group and contains one formula unit per elementary cell. Using the methods of modulation spectroscopy (reflection and absorption ) we determined the optical band gap of CdInGaS4 crystals which equals 2.93 eV at room temperature.plates (8x8 Ynm ) in 8 1 8 geometry using the vacuum grating spectrometers FIS-3 and FIS-21 with wire-grid polariser for the spectral range 400 to -5 cm carried out on the UR-20 spectrometer. The reflectivity from freshly cleaved surfaces in 8 1 8 geometry was compared with the reflectivity curve obtained from polished surfaces containing the 8-axis in the same geometry. The results were in good agreement. The resolution in the investigated region was not worse than 2 cm-l. The frequency of transverse (TO) and longitudinal.(LO) optical phonons for both polarizations was determined by Kramers-Kronig integration. TO frequencies were also determined by direct transmission measurements of thin cleaved (3 to 8 pm) crystals (the morphology of the crystals permitted easy cleavage in the direction perpendicular to the C-axis) in E 1 C geometry.Near-normal reflectivity was measured on freshly cleaved mirror-like 2 -1 . The measurements in the spectral range 600 to 400 cm-l were -+ + -D
BYCdInAlS4 is one of the less investigated semiconductors among the complex ones with layered structure. This compound is the crystal analog of CdInGaS4, first synthesized by Shand /l/. Polarized far-infrared (IR) reflection spectra and Raman scattering from CdInGaS4 single crystals have been investigated in /2/ and /3/, respectively. ments of CdInAlS4 single crystals in the spectral range 5000 to 100 cm'l, by help of FIS-3 and UR-20 spectrometers. The single crystals were grown by the chemical transport method in an evacuated quartz tube, using iodine as a transport agent. Grown crystals were plate-like and had one prominent c l e a v s e plane perpendicular to the C axis (which coincided with the optical axis). The directionof the optical axis was controlled by the conoscopic picture with help of a MIN-1 microscope. The measurements were performed on freshly cleaved mirror-like plates (5x5 mm ) in E 1 C geometry. The thickness of the samples varied from 5 to 500 y m . The resolution in the investigated region was not worse than 2 cm . According to /3/ one of the possible space groups for the crystals with CdInGaS4 type structure is Did. The normal modes of vibration at the center of the Brillouin zone can be described by the irreducible representations of the point group D3d:In this note we give the first results of polarized transmission measure--b 2 -+ -b -1 I?=?% + 7 4 2 u + 7 E + 7 E U , g gwhere +u + EU and spectively. According to the selection rules there should be 7 % + 7E Raman and 6 AZu + 6 E IR active phonons. U 9 in the layer plane (E -type phonons). + E are the acoustic and interlayer vibrations, reg g g The thickness of our crystals permitted to observe only the phonons polarized U 1) Prospekt Narimanova 33, 370 143 Baku, USSR.
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