INFLUENCE OF SURFACE DISORDER ON RHEED PATTERNS FROM GAAS(001)-2X4 SURFACES

Abstract

Reflection high-energy electron diffraction measurements have been carried out for a nearly perfect and a disordered GaAs(001)-2 x 4 surface in the [1BAR10] azimuth. The surfaces were prepared in-situ by molecular beam epitaxy and the measurements were made at a substrate temperature of 560-degrees-C under different flux conditions, giving the different degrees of surface ordering. Diffracted intensity distributions along various reciprocal surface lattice rods were measured for different angles of incidence using a primary beam energy of 15 keV. Drastic differences with surface order were found for both the (quasi) elastically diffracted beams (rocking curves) and the diffuse beams. The rocking curves can be interpreted largely by Bragg reflection from the bulk crystal and a number of causes for the intensity changes are given. In the case of the disordered surface the intensity distributions along the reciprocal lattice rods are dominated by broad diffuse peaks which occur at the intersection of reciprocal rods and Kikuchi lines. It is shown that while a kinematical model is unable to explain the experimental observations, a previously published model provides a very satisfactory interpretation.