TRANSMISSION ELECTRON-MICROSCOPY INVESTIGATION OF AGGASE2 SINGLE-CRYSTALS AND STUDY OF ANNEALING EFFICIENCY BY ELECTRICAL-CONDUCTIVITY MEASUREMENTS

As-grown AgGaS2 and AgGaSe2 crystals contain a high density of precipi tates which cause optical scattering. From a transmission microscopy a nalysis we have observed the structure of Ga2Se3-rich inclusions in th e middle of the crystalline matrix. Annealing effect on electrical con ductivity of AgGaX2 (X = S or Se) single crystals has been investigate d. It has been shown that these inclusions are responsible for electri cal instabilities. After one month annealing in presence of Ag,S and a n additional month in presence of Ag,S and S,, the electrical conducti vity of the AgGaS2 crystal is found to be reversible with temperature. An energy level is observed in the band gap. Both the nature and the relative position of this level to the band edges has not yet been det ermined, however, it may be due to sulphur vacancies as the conductivi ty is n-type. After two months annealing in presence of Ag2Se, the AgG aSe2 single crystal exhibits an intrinsic semiconducting temperature d ependence showing reversible behaviour. (C) 1998 Elsevier Science B.V. All rights reserved.