TEM examination of dislocations generated in GaAS photocathode structures

Abstract

Basic studies have been performed on GaAs epitaxial multilayer structures of the type used for transmission photocathodes. The substrates were horizontal Bridgman (100)GaAs, and the layers either GaAs or GaAlAs grown by the LPE method and Zn-doped. TEM examinations were made to determine the nature and distribution of dislocations present in the structures, deduce how they were formed and suggest how they might be eliminated. Special attention was given to those dislocations formed by surface stresses generating 60° dislocations with at the specimen surface and moving down on inclined {1ll} slip planes to form a network at an underlying interface. One feature of the work was the TEM examination of ∽ 1° angle-lap and 90° cross-section thinned specimens to determine the three-dimensional distribution of the dislocations. Results are reported for three different aspects of the work.First, when GaAs layers are grown by the LPE method.