STEPS AND ISLANDS ON VICINAL SILICON (001) SURFACES GROWN BY MOLECULAR-BEAM EPITAXY IN AN AS4 ATMOSPHERE

Step arrays on Si(001) surfaces misoriented by 1.6-degrees toward [110] have been studied by reflection high-energy electron diffraction (RHEED) during growth and annealing in a growth chamber for GaAs molecular-beam epitaxy (MBE). Heating of As-coated surfaces in the MBE chamber resulted in background chamber pressures on the order of 10(-8) Torr, an atmosphere quite different from that used in most previous studies on Si surfaces. Changes in the relative coverage of (1 x 2) and (2 x 1) terraces have been monitored by recording RHEED half-order-spot intensities and intensity profiles of the specular streak. In contrast to reported behavior on clean surfaces, we find that below a critical temperature of about 700-degrees-C the relative coverage of (1 x 2) and (2 x 1) reconstructed terraces cannot be strongly affected by growth. Above this temperature, a step-flow mechanism leading to a double-layer-stepped surface acts in the early stages of growth. There is, however, some nucleation of islands from the very beginning of growth. The reordering of these islands leads to a degradation of the double-layer-stepped character of the surface after growth.