GROWTH ANISOTROPY OBSERVED ON SI(001) SURFACES DURING SI-GSMBE USING DISILANE

Bilayer reflection high energy electron diffraction (RHEED) intensity oscillations were observed during growth on double-domain Si(001)(2 X 1) + (1 X 2) substrates during silicon gas source molecular beam epitaxy (Si-GSMBE) using disilane. A transition from monolayer to bilayer mode oscillation behaviour was observed in the [110] azimuths during growth. Oscillations began with an asymmetric monolayer waveform which transformed into an apparent bilayer mode following several oscillation periods. Simultaneous measurement of RHEED intensity oscillations of the specular beam and (1 X 2) and (2 X 1) reconstruction related beams in the [010] azimuth showed that bilayer oscillations resulted from alternating surface reconstructions. The emergence of these bilayer oscillations during growth is discussed on the basis of the anisotropic growth kinetics on Si(001) surfaces which results in a preference of type-B domains. RHEED measurements made following growth on vicinal substrates reveal that diffraction features arising from type-B terraces show a marked increase in intensity, while type-A domain features decrease, confirming that the anisotropy results in a preferred growth on type-B terraces. Temperature studies reveal that at substrate temperatures above 600-degrees-C, this anisotropy disappears and RHEED intensity variations resume "normal" monolayer-mode growth behaviour.