GROWTH DYNAMICS OF GAAS, ALAS AND (AL,GA)AS ON GAAS(110) AND GAAS(111)A SUBSTRATES DURING MOLECULAR-BEAM EPITAXY

The growth dynamics of GaAs, AlAs and (Al, Ga)As films grown by molecu lar beam epitaxy (MBE) on GaAs (1 1 0) and (1 1 1)A substrates have be en studied using re;flection high energy electron diffraction (RHEED) intensity oscillations and scanning tunnelling microscopy (STM). In co ntrast to growth on (0 0 1) oriented substrates, the period of the RHE ED intensity oscillation does not in general provide a measure of the growth rate. This is explained by the very different surface chemistry involved, since the short lifetime of arsenic molecules (As, or As-4) on non-(0 0 1) surfaces results in cation-stable surface conditions, which generate arsenic (anion)- induced intensity oscillations, wherea s on (0 0 1) surfaces they are cation-induced under all normal growth conditions. The effects of this behaviour on surface morphology are il lustrated, as are the relative influences of Ga and Al. STM images obt ained during the first few monolayers of growth provide a detailed ind ication of the growth mode and in particular explain in a simple manne r the origin of bilayer period RHEED intensity oscillations: obtained during growth on GaAs (1 1 0).