From Layer-by-Layer Growth to Nanoridge Formation: Selective Area Epitaxy of GaAs by MOVPE

We outline the growth mechanismand shape evolution of GaAsnanoridges by selective area MOVPE with three well-identified, distinctstages of growth. Selective area epitaxy at the nanoscale enables fabricationofhigh-quality nanostructures in regular arrays with predefined geometry.Here, we investigate the growth mechanisms of GaAs nanoridges on GaAs(100) substrates in selective area trenches by metal-organicvapor-phase epitaxy (MOVPE). It is found that pre-growth annealingresults in the formation of valley-like structures of GaAs with atomicterraces inside the trenches. MOVPE growth of GaAs nanoridges consistsof three distinct stages. Filling the trench in the first stage exhibitsa step-flow growth behavior. Once the structure grows above the masksurface, it enters the second stage of growth by forming {101} sidefacets as the (100) flat top facet progressively shrinks. In the thirdstage, the fully formed nanoridge begins to overgrow onto the maskwith a significantly reduced growth rate. We develop a kinetic modelthat accurately describes the width-dependent evolution of the nanoridgemorphology through all three stages. MOVPE growth of fully formednanoridges takes only about 1 min, which is 60 times faster than inour set of molecular beam epitaxy (MBE) experiments reported recently,and with a more regular, triangular cross-sectional geometry definedsolely by the {101} facets. In contrast to MBE, no material loss dueto Ga adatom diffusion onto the mask surface is observed in MOVPEuntil the third stage of growth. These results are useful for thefabrication of GaAs nanoridges of different dimensions on the samesubstrate for various applications and can be extended to other materialsystems.