CRYSTAL-GROWTH OF ZNSE FROM THE MELT

High quality zinc selenide (ZnSe) substrate crystals which can be grow n at low cost are required for a new generation of laser diodes emitti ng in the blue-green region of the spectrum. The most efficient growth method, which is successfully applied in the production of other semi conductor crystals, has not yet provided a sufficient yield. Melt grow th of bulk ZnSe crystals is impaired by unfavorable material propertie s. In addition to the high melting point and deviation from stoichiome try due to incongruent evaporation the pronounced tendency for twinnin g is the most limiting property. This review gives a survey of the var ious experimental approaches adopted to master these obstructions and summarizes the available physicochemical and thermodynamic data releva nt for crystal growth. Both composition and thermal history of the mel t are shown to have a decisive influence on the defect formation durin g crystallization and cooling of the grown crystal. Post growth therma l 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 f or the prevention of multi-twinning is given.