CHARACTERISTICS OF FACETS IN SI-DOPED GAAS CRYSTALS GROWN BY HORIZONTAL BRIDGMAN TECHNIQUE

Dislocation free Si-doped GaAs crystals, 2 inches in diameter, 30 cm in length and carrier concentration of 1018 cm-3, have been growm by horizontal Bridgman (HB) technique. Large facets were found to be more prone to form under a longitudinal temperature gradient less than 1°C/cm. Characteristics of facets in these HB grown GaAs crystals have been investigated. The occurence of large facets resulted in the lifting of the top surface of the crystal. Facets were found to be more prone to form by reducing the temperature gradient, increasing the Si-dopant concentration and the growth rate. Perpendicular twins, which were related to the (1̄, 1̄, 1̄) facet growth, were generated at the positions where the facet size varied drastically. These twins were identified to be 60° rotation twins by chemical etching method. The carrier concentration of the facet area, as measured by Van der Pauw and spreading resistance methods, was found to be 1.7-2.0 times higher than that of the non-facet area. The dislocations in the non-facet area were observed to terminate at the boundary of facet and non-facet areas. © 1990.