Structural and defect characterization of CuInS2 single crystals grown under elevated pressures

By using an argon overpressure, large CulnS2 single crystals were produced. Upon modification of the temperature gradient over the melt a change of structural features was induced. Low temperature gradients resulted in the growth of large single crystals, whereas for increased temperature gradients sheet-like material was prepared. The lamellar material cleaved along the (112) planes as revealed by reflection high-energy electron diffraction, and the appearance of Kikuchi lines indicates good crystallinity. Within the limits of X-ray diffraction the material was shown to be single-phase CulnS2. IR measurements were employed for comparison of materials with different structural properties. Possible origins for the new lamellar structure are discussed. Additional information obtained by a new angle-resolved reflection spectroscopy on the defects in CulnS2 single crystals is presented. The method permits the room temperature detection of small variations of the complex dielectric function £. The variation of £ = £1 + i£2 is correlated to the defect centres and their energetic position in the band gap. The defect levels determined from this method are compared with photoluminescence and transmission spectroscopy results.