PNNL

Abstract

The growth-tip region of a high-purity 4.2-cm diameter Ge boule grown using low-pressure Bridgman methods in a vertical gradient freeze furnace was sectioned and polished in preparation for scanning electron microscopy and was characterized using electron backscatter diffraction (EBSD). The boule had a characteristic conical tip region with cone angle of 40° of a right circular cylinder from which a section was taken along the boule longitudinal centerline with an approximate surface area of 4 cm2. The majority of this surface area was characterized using EBSD and an image collage was assembled for the tip region. The grain structure, grain boundary orientation, twin structure, and overall crystal growth direction were determined. A crystal growth direction of approximately was observed, which was also identified as the growth direction of several prominent twins observed in the tip region. The grain structure of the tip region appeared to be controlled by the sidewall nucleation of a stray grain that competed for dominance during growth. Grain boundaries and triple grain junctions were identified as low-energy coincident-site-lattice (CSL) boundaries and junctions of the S3 and S9 types.