Behavior and mechanism of step bunching during metalorganic vapor phase epitaxy of GaAs

The behavior of step bunching during GaAs growth for metalorganic vapor phase epitaxy is investigated by varying growth temperatures and substrate misorientation angles. It is found that monolayer step-flow growth changes to step-bunching growth when the misorientation angle, that is, the substrate surface step density, increases to a certain value, showing the existence of a critical step density. This critical value decreases with increasing growth temperature. The bunched terrace width does not depend on the misorientation angle, but it increases with growth temperature. We propose that the transition to step bunching from step-flow growth occurs when the concentration of Ga adatoms at the step edges is less than the equilibrium concentration. Various bunching characteristics are explained using this model.