Ga Adlayer Governed Surface Defect Evolution of (0001)GaN Films Grown by Plasma-Assisted Molecular Beam Epitaxy

The impact of the Ga adlayer coverage onto the surface morphologies and pit densities of GaN (0001) films grown by plasma-assisted molecular beam epitaxy (PAMBE) has been studied using quantitative in situ quadrupole mass spectrometry (QMS). As the equilibrium Ga adlayer coverages rise continuously from 0 to 2.5 monolayers (ML) the surface pit densities decrease from ∼2×109 cm-2 to zero, yielding characteristic step-flow and spiral growth hillock features. These results show that there is a direct and quantitative link between Ga adlayer coverage, adatom diffusion and surface defect structure without any discontinuities.