Energy Barrier For Incorporation Research Articles

As/Ga ratio dependence of Ga adatom incorporation kinetics at steps on vicinal GaAs(001) surfaces

Systematic measurement of the growth kinetics on the transition from growth by cluster formation and coalescence to growth by step advancement on vicinal surfaces during MBE growth of GaAs(001) films has revealed that the first maximum of the RHEED intensity oscillation is gradually delayed (the period increases) as the growth mode transition temperature is approached from below. This is a direct consequence of the gradual change of the growth mode with temperature; as more atoms are involved in the step propagation mode, the number available for island nucleation decreases, with a resultant increase in the period. We have reported that detailed analysis of this delay allows us to investigate the incorporation kinetics of Ga adatoms into step edges and that the energy barrier for incorporation is considerably higher for Ga- than for As-terminated steps. Here we have examined the As/Ga ratio dependence of the Ga incorporation mechanisms using this technique and have found that the incorporation rate for Ga-terminated steps is enhanced while that for As-terminated steps is reduced as the As/Ga ratio is increased near transition temperatures. It suggests that additional arsenic enhances incorporation kinetics into the Ga-terminated steps via As-As dimers but blocks the sites on the As-terminated steps.

Ga adatom incorporation kinetics at steps on vicinal GaAs (001) surfaces during growth of GaAs by molecular beam epitaxy

We have systematically examined the transition from two-dimensional nucleation to step-flow growth on variously misoriented vicinal GaAs (001) surfaces during molecular beam epitaxy using reflection high-energy electron diffraction (RHEED). The time to the first maximum of the RHEED intensity oscillations is gradually delayed as the growth mode transition temperature is approached from below as the result of an increasing number of adatoms being incorporated at steps. Detailed analysis of this delay has shown that the incorporation rate is independent of the Ga flux, but it is strongly dependent on the direction of misorientation. This means that step edges do not act as perfect sinks for adatoms, but that detachment can occur relatively easily. The energy barrier for incorporation is considerably higher for Ga- than As-terminated steps, which strongly suggests that the anisotropic growth mode transition on GaAs (001) stems mainly from the different step structures rather than anisotropic Ga adatom migration.