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Scattering centers in as grown AgGaS2 crystal

Konstantin A. Kokh 1,2Dmitry Kokh 1

1. Institute of Geology and Mineralogy SB RAS (IGM), Koptyuga ave., 3, Novosibirsk 630090, Russian Federation
2. Novosibirsk State University (NSU), Pirogov 2, Novosibirsk 630090, Russian Federation

Abstract

Many crystals with chalcopyrite structure possess outstanding nonlinear optical properties. A common feature of these compounds is the presence of scattering centers in as-grown crystals due to decay of the solid solutions. While the basic principles of how to suppress the centers are known, this contribution is aimed to detailed microscopic study of these defects on the example of AgGaS2 (AGS) crystals. Due to high sulfur pressure at the melting point of AGS (996˚C) a separate synthesis of raw material is necessary. In this work the synthesis of AGS was performed by direct fusion of the elementary compounds in the single-zone furnace. Then, the charge was placed in the double-wall ampoule for recrystallization by modified Bridgman method.  Thin plates of AGS from as-grown crystal as well as from that annealed in Ag2S and Ga2S3 atmosphere were taken for study. The annealing was done by heating the sample and the boat with agent in evacuated quartz ampoules. Various times and temperatures were tested. No difference was found between the samples by X-ray diffraction and Raman measurements. However, according to EDS X-ray microprobe analysis, the scattering centers consist from inclusions of Ag2Ga20S31 phase. Elimination of these inclusions takes place after annealing of the samples in the atmosphere of Ag2S. Diffusion of Ag-rich components into the bulk of AGS determines the time of annealing. Around 2 weeks are necessary for boundary between milky and optically clear AGS to propagate at 1 cm inside the sample at 850˚C. The composition of inclusions is also confirmed by the fact that annealing with Ga2S3 makes the inclusions larger which in turn results in cleavage micro cracks in the sample. A certain attention has been paid to acid etching of the samples. The treatment in HCl revealed morphological feature of the plate like inclusions which explains why they look like a dot-lines in transmitted light. Also this acid effectively dissolves defective outer layer on the polished surface of the AGS, while the undamaged cleavage plane {112} remains unchanged. On the other hand HNO3 reacts with any surface of AGS, so this acid is suitable to reveal etch pits.

 

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Related papers

Presentation: Poster at 17th International Conference on Crystal Growth and Epitaxy - ICCGE-17, General Session 7, by Konstantin A. Kokh
See On-line Journal of 17th International Conference on Crystal Growth and Epitaxy - ICCGE-17

Submitted: 2013-04-05 12:21
Revised:   2013-04-05 12:22