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