Study of the pseudo-(1×1) surface by RHEED and XPS for InGaN/GaN (0001)/Al₂O₃ heterostructures grown by PA-MBE

In this letter, we report on the study of the pseudo-(1×1) surface by reflection high-energy electron diffraction in the InGaN grown on GaN/sapphire substrate by plasma-assisted molecular beam epitaxy. At the end of the InGaN layer growth at 500 °C the formation of a (1×1) diffraction pattern along the [11-20] azimuth was observed. By decreasing the temperature to 330 °C distinct sidebands appear on the high wave vector sides of these first-order streaks. The observation of this kind of 1/6-satellite peaks is then related with the formation of an outmost metal bilayer. From atomic force microscopy, nanometer-size surface structures consisting of hexagonal rows are observed. X-ray photoelectron spectroscopy analysis reveals relatively smaller concentration of Ga as compared with In within the surface area than in the bulk of the InGaN layers. We explain the results by means of the surface In segregation and proposed a possible model for the In-bilayer atomic surface distribution.