Abstract
The stacking sequence of hexagonal close-packed and related crystals typically results in steps on vicinal {0001} surfaces that have alternating A and B structures with different growth kinetics. However, because it is difficult to experimentally identify which step has the A or B structure, it has not been possible to determine which has faster adatom attachment kinetics. Here we show that in situ microbeam surface X-ray scattering can determine whether A or B steps have faster kinetics under specific growth conditions. We demonstrate this for organo-metallic vapor phase epitaxy of (0001) GaN. X-ray measurements performed during growth find that the average width of terraces above A steps increases with growth rate, indicating that attachment rate constants are higher for A steps, in contrast to most predictions. Our results have direct implications for understanding the atomic-scale mechanisms of GaN growth and can be applied to a wide variety of related crystals.
Highlights
The stacking sequence of hexagonal close-packed and related crystals typically results in steps on vicinal {0001} surfaces that have alternating A and B structures with different growth kinetics
A ubiquitous but subtle version of this effect occurs on the basal-plane {0001}-type surfaces of crystals having hexagonal close-packed (HCP) or related structures, which are normal to a 63 screw axis
These features are consistent with predictions that A and B steps have significantly different attachment kinetics[6,8,12,16,17,18,19,20,21,22] that lead to unequal local fractions of α and β terraces during growth
Summary
The stacking sequence of hexagonal close-packed and related crystals typically results in steps on vicinal {0001} surfaces that have alternating A and B structures with different growth kinetics. A ubiquitous but subtle version of this effect occurs on the basal-plane {0001}-type surfaces of crystals having hexagonal close-packed (HCP) or related structures, which are normal to a 63 screw axis These features are consistent with predictions that A and B steps have significantly different attachment kinetics[6,8,12,16,17,18,19,20,21,22] that lead to unequal local fractions of α and β terraces during growth. It has not been possible to experimentally distinguish the terrace orientation or step structure, and to determine whether A or B steps have faster kinetics
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