Residual Gas Measurements and Morphology Characterization on Grown Crystals

Abstract

After the growth of the crystals, the samples have been evaluated through a comprehensive characterization plan. The first part of characterizations, which included the residual gas measurements on selected ampoules and the studies on the morphology of the grown crystals, are presented in this chapter. The residual gas pressures and compositions measured after growths with the source materials from different vendors suggested that the H₂ reduction and dynamic baking heat treatment are essential in providing a reproducible environment of low residual gas pressure during each growth. On the morphology of the grown ZnSe crystals, although in the vertical configuration, the crystals grew in full contact with the wall to the full diameter of the ampoule, but, frequently, the crystals grown in the horizontal configuration grew away from the ampoule wall without any contact. From the observations under scanning electron microscope (SEM) and atomic force microscope (AFM), the growing surface of a horizontal grown crystal, consists of terraces of the orientation of (110) with numerous steps between the terraces and the crystal grew by the extending of these steps. However, from the microscopy on the as-grown surface of vertical grown crystals, the growth mechanism can be viewed as island mode with nucleation of islands in the order of 10 nm in height. The morphologies by visual observation and the micro-morphology of grown surface by SEM and AFM have been examined for the growths of self-seeded and seeded ZnSe and CdTe, self-seeded ZnSe doped with transition metals, self-seeded ZnSeTe, CdS and ZnTe.