Optical and electrical properties of AgIn(SSe)(2) crystals

AgIn(SxSe1-x)(2) (X = 0-1.0) crystals were grown by a vertical gradient fre ezing (VGF) method. All samples indicated chalcopyrite structures and n-typ es by means: of X-ray diffraction (XRD) and thermoprobe analysis, respectiv ely. All crystals were slightly found to be Se- and S-rich by the electron probe microanalysis (EPMA). The samples were also In-poor in X <0.5 and Ag- poor in X >0.5. The AgIn(S0.5Se0.5)(2) (X = 0.5) crystal was mostly close t o the stoichiometry. Lattice constants of a and c axes calculated by the XR D patterns were found to be proportional to X, indicating that they obeyed Vegard's law. In the photoluminescence (PL) spectra at 77 K, the crystals w ere highly pure because a free exciton (FE) emission line was clearly obser ved. It was clear that the FE peak energy showed a nonlinear dependence on the composition X values in the AgIn(SXSe1-X)(2) crystal. The bowing parame ter was estimated to be 0.25 eV. After the AgInSe2 crystal was annealed at 640 degreesC under a vacuum atmosphere in the AgInSe2 crystals, the optical quality was improved because the FE peak clearly appeared and the donor-ac ceptor pair emission band disappeared in the PL spectra. (C) 2001 Elsevier Science B.V. All rights reserved.