ROLE OF STEPS IN EPITAXIAL-GROWTH

The role of steps in the epitaxial growth of quantum structures is dis cussed. We present experimental results and theoretical predictions of growth on stepped surfaces. Scanning tunneling microscopy (STM) image s of molecular beam epitaxy grown GaAs(001) surfaces misoriented by 1 degrees and 2 degrees towards the(111)A direction show non-uniform ter races with a peak in the terrace width distribution at 40 Angstrom. Si mple models of atoms landing on a step and attaching at the ascending step edge, however, predict an equalization of terrace widths. A therm odynamic model which allows the steps to move freely with the constrai nt that it costs energy to form a kink predicts step bunching for high kink energies. Steps on vicinal surfaces have been utilized for growi ng quantum wire structures using a technique where fractional monolaye rs of different materials are deposited on a stepped surface, leading to the creation of a lateral superlattice (LSL). The terrace width uni formity is observed by STM to improve dramatically with the growth of an AlAs-GaAs LSL. Cross-sectional transmission electron microscopy of LSLs shows good segregation of the composite layers.