A model for the appearance of chevrons on RHEED patterns from InAs quantumdots

Reflection high energy electron diffraction patterns from quantum dots form ed by depositing InAs on to GaAs(0 0 1) show pairs of streaks known as chev rons. A clear understanding of the mechanism by which chevrons are produced does not seem to exist in the literature, and both pure diffraction mechan isms and effects due to the refraction of electrons have been put forward. Scanning tunnelling microscopy has shown that these particular quantum dots have bounding surfaces which are curved, not planar. In this paper, a mode l is presented for the explanation of the production of chevrons from such quantum dots in terms of pure refraction effects. A method is given for det ermining the grazing angles of incidence of the various diffracted beams on the curved bounding surfaces of the quantum dots, and hence the refractive deviations have been calculated as a function of the direction of the inci dent electron beam. It is shown that the model provides a semi-quantitative explanation of the occurrence of the chevrons: (C) 2001 Elsevier Science B .V. All rights reserved.