Non-stoichiometry and point native defects in non-oxide non-linear optical large single crystals: advantages and problems

Abstract

Advances and limitations in the field of growing large, high optical quality single crystals of AgGaS₂ (AGS), AgGaGeS₄ (AGGS), ZnGeP₂ (ZGP), LiInS₂ (LIS), LiGaS₂ (LGS), LiInSe₂ (LISe), LiGaSe₂ (LGSe) and LiGaTe₂ (LGT) compounds are considered in this contribution. With attendant good optical quality, all as-grown crystals of these compounds contain always some amount of native defects which adversely affect the optical and electrical properties. With the aim of overcoming this limitation, attention in this review is focused on concepts that provide a better insight into origins of non-stoichiometry and mechanism of native point defect occurrence. Among these concepts, preference is given to effective ways of determining the scale of the non-stoichiometry through the study of T–X and P–T diagrams, to promising techniques characterizing precisely phase purity, spatial chemical inhomogeneity, and amount of microstructural inclusions in grown crystals, and to measuring thermodynamic and thermochemical properties of the compounds. Utility of physicochemical characteristics for optimizing the growing process is considered. A combination of chemical information and physical properties of crystals is obligatory for clarifying the origins of defects. Attention is given to clarifying specificity of growing Li-containing crystals caused by high chemical activity of the Li component. With such content, this review paper presents status of current knowledge of non-stoichiometry and defects of crystals demanded in practice for non-linear optics.