Molecular dynamics studies of defect formation during heteroepitaxial growthof InGaN alloys on (0001) GaN surfaces

摘要

We investigate the formation of extended defects during molecular-dynamics (MD) simulations of GaN and InGaN growth on (0001) and (112¯0) wurtzite-GaN surfaces. The simulated growths are conducted on an atypically large scale by sequentially injecting nearly a million individual vapor-phase atoms towards a fixed GaN surface; we apply time-and-position-dependent boundary constraints that vary the ensemble treatments of the vapor-phase, the near-surface solid-phase, and the bulk-like regions of the growing layer. The simulations employ newly optimized Stillinger-Weber In-Ga-N-system potentials, wherein multiple binary and ternary structures are included in the underlying density-functional-theory training sets, allowing improved treatment of In-Ga-related atomic interactions. To examine the effect of growth conditions, we study a matrix of >30 different MD-growth simulations for a range of InxGa1-xN-alloy compositions (0 ≤ x ≤ 0.4) and homologous growth temperatures [0.50 ≤ T/T^*m(x) ≤ 0.90], where T^*m(x) is the simulatedmelting point. Growths conducted on polar (0001) GaN substrates exhibit theformation of various extended defects including stacking faults/polymorphism, associated domainboundaries, surfaceroughness, dislocations, and voids. In contrast, selected growths conductedon semi-polar (112¯0) GaN, where the wurtzite-phase stacking sequence is revealed at thesurface, exhibit the formation of far fewer stacking faults. We discuss variations in thedefect formationwith the MD growth conditions, and we compare the resulting simulatedfilms toexisting experimental observations in InGaN/GaN. While the palette of defects observed by MD closelyresembles those observed in the past experiments, further work is needed to achieve trulypredictive large-scale simulations of InGaN/GaN crystal growth using MDmethodologies.