Defect structure of Langasite-type crystals: a challenge for applications

Whereas quartz crystals are grown hydrothermally, langasites are grown from the melt, by Czochralski. Particularities of this growth method and inherent physicochemical properties of these materials lead to a specific defect structure, which actually limits reproducibility in device parameters. In this study, crystals and wafers grown in different laboratories worldwide have been investigated. Striations, inclusions, voids, dislocations, and faceting effects are discussed in terms of their origin and 3D distribution/pattern within the samples, and their effects on device properties (when known). Ways to improve the quality of Czochralski grown langasites and ideas for future materials developments are also given.