The surface morphology evolution of N-polar GaN with growth time was investigated and compared with Ga-polar GaN. N-polar GaN directly grown on SiC substrates was found to have slower three-dimensional (3D) to two-dimensional (2D) growth transformation and lesser coalescence than the Ga-polar counterpart, resulting in rougher surface morphology, whereas the AlN nucleation layer (NL) accelerated 3D to 2D transformation, resulting in smoother surface morphology. N-polar GaN was found to have mound-type surface morphology with clustered atomic steps, unlike the regular screw-type dislocation-mediated step-flow growth observed for Ga-polar GaN. This was explained by the lower diffusion of adatoms on the N-polar surface due to its higher surface energy and higher Ehrlich-Schwoebel barrier (ESB). In addition, the increased III/V ratio in N-polar GaN growth was found to reduce the surface roughness from 2.4 nm to 1 nm. Without Si doping, the N-polar GaN HEMT heterostructures grown under optimized conditions with smoother surface morphologies exhibited sheet carrier density of 0.91 × 1013 cm-2 and mobility of 1220 cm2/V∙s. With Si δ-doping, the sheet carrier density was increased to 1.28 × 1013 cm-2 while the mobility was reduced to 1030 cm2/V∙s. These results are comparable to the state-of-the-art data of PA-MBE-grown N-polar GaN HEMT heterostructures on SiC substrates.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.