Twin boundaries in GaAs grown on Ge

Abstract

Interest in the structure of grain boundaries in semiconductors has been increasing for many reasons including the important role of boundaries on the electrical behavior of polycrystalline materials. GaAs is of interest because of its particular electrical properties such as its direct band gap and high electron mobility. Specific bicrystals of GaAs were produced on substrates cut from Czochralski-grown germanium bicrystals in a low-pressure organometallic vapor- phase epitaxy system. When the growth surface was parallel to the (110) plane, many microtwins were produced in the GaAs epilayer. The structure of twin boundaries in GaAs can take two forms depending on the relative polarities of the two adjoining grains because GaAs has a sphalerite structure which is a face-centered cubic lattice with a two atom basis. The polarity of the two grains meeting at the grain boundaries can be determined by using the dynamical coupling effects of high-order Laue-zone reflections on the (200) and (200) diffracted beams.