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 precipitates which cause optical scattering. From a transmission microscopy analysis we have observed the structure of Ga2Se3-rich inclusions in the middle of the crystalline matrix. Annealing effect on electrical conductivity of AgGaX2 (X = S or Se) single crystals has been investigated. It has been shown that these inclusions are responsible for electrical instabilities. After one month annealing in presence of Ag,S and an additional month in presence of Ag,S and S,, the electrical conductivity 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 determined, however, it may be due to sulphur vacancies as the conductivity is n-type. After two months annealing in presence of Ag2Se, the AgGaSe2 single crystal exhibits an intrinsic semiconducting temperature dependence showing reversible behaviour. (C) 1998 Elsevier Science B.V. All rights reserved.