Crystal growth of ZnSe from the melt

High quality zinc selenide (ZnSe) substrate crystals which can be grown at low cost are required for a new generation of laser diodes emitting in the blue-green region of the spectrum. The most efficient growth method, which is successfully applied in the production of other semiconductor crystals, has not yet provided a sufficient yield. Melt growth of bulk ZnSe crystals is impaired by unfavorable material properties. In addition to the high melting point and deviation from stoichiometry due to incongruent evaporation the pronounced tendency for twinning is the most limiting property. This review gives a survey of the various experimental approaches adopted to master these obstructions and summarizes the available physicochemical and thermodynamic data relevant for crystal growth. Both composition and thermal history of the melt are shown to have a decisive influence on the defect formation during crystallization and cooling of the grown crystal. Post growth thermal treatment can be used to affect the equilibrium of point defects and the related electronic and optical properties as well as the crystal structure. Based on a close look at the mechanism of twin formation in ZnSe and the first empirical results on twin reduction a hypothesis for the prevention of multi-twinning is given.