In Situ Microbeam Surface X-ray Scattering Reveals Alternating Step Kinetics During Crystal Growth

TL;DR

This study uses in situ microbeam surface X-ray scattering to determine the step-specific growth kinetics on vicinal GaN surfaces, revealing that A steps have faster adatom attachment rates, challenging previous predictions.

Contribution

It introduces a novel application of in situ X-ray scattering to identify step-specific kinetics during crystal growth, providing new insights into GaN surface dynamics.

Findings

A steps have higher attachment rate constants than B steps.

Terrace widths above A steps increase with growth rate.

Results challenge most existing predictions about step kinetics.

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.