Influence of the crucible shape on the formation of facets and twins in the growth of GaAs by the vertical gradient freeze technique

The influence of the shape of the crucible on the growth of silicon-doped GaAs crystals by the vertical gradient freeze (VGF) technique is investigated by using four different angles Φ (60°, 90°, 120°, 144°) of the conical part of the pBN crucible. We find a decrease of the length of the {1 1 1} edge facets in the conical region with increasing cone angle Φ. The {1 1 1}As facets are always larger and show a higher tendency to twinning compared to {1 1 1}Ga facets. The model of Hurle (J. Crystal Growth 147 (1995) 239) which correlates the formation of twins with the growth of facets at the three phase boundary (TPB) is confirmed. The maximum angle between the edge facet and the extension of the crystal surface at which the facet should detach from the TPB is found experimentally to be between 95.3° and 107.3°, which corresponds well with the value of 104° calculated by Hurle for encapsulated GaAs.