Recrystallization of CVD-ZnS during thermal treatment

Abstract

Polycrystalline ZnS taken from an industrial chemical vapor deposition (CVD) process was thermally treated with and without hot isostatic pressing (HIP). Both annealed materials show an increased light transmittance in the visible range, a recrystallized and reorganized microstructure as well as an absence of the Zn-H bonds observed in CVD-ZnS. However, the increased light transmission essential for most optical applications is only observed in the HIP-ZnS. This is caused by a significantly reduced porosity of the material. The majority of pores initially form at grain boundaries during thermal treatment and the application of simultaneous high pressure reduces their number to a minimum. X-ray diffraction (XRD), scanning electron microscopy (SEM) including electron back scatter diffraction (EBSD) as well spectroscopic measurements and optical microscopy are used for analysis. It is concluded, that the density of crystal faults in CVD-ZnS is significantly reduced by the HIP-step.