Effect of composition gradient on CuIn3Te5 single-crystal properties and micro-Raman and infrared spectroscopies

Several CuIn3Te5 single-crystal samples grown by the vertical Bridgman method have been studied. Changes in composition of the In/Cu atomic ratios in the 3.45-1.88 range have been detected along the ingots by X-ray energy-dispersive analysis. In the first-to-freeze region, Cu excess and In and Te depletions appear. From X-ray powder diffraction data we conclude that the crystals show the P-chalcopyrite-type structure, space group P (4) over bar 2c, with lattice parameters alpha = 6.1713 angstrom and c = 12.329 angstrom, similar to that found in CuIn3Se5. The optical energy gaps, as determined by spectral ellipsometry, lie in the 1.83-1.93 eV range and change with composition. Micro-Raman spectra and infrared reflectance measurements confirm the presence of the crystallographic phase CuIn3Te5 and indicate a highly ordered Te sublattice and disordered Cu and In sublattices. Conduction types n and p are found, suggesting the possibility of intentional doping. The crystal density and gaps seem appropriate for their use in gamma-ray detectors.