Direct observation of inversion domain boundaries of GaN on c-sapphire at sub-ångstrom resolution

Abstract

The direct observation of inversion domain boundaries (IDB) of GaN on c-Sapphire at sub-angstrom resolution was investigated. A ca. 1 μm thick GaN film was grown directly on c-sapphire at a temperature of 1030°C with a V/III ratio of around 100 by low-pressure metal-organic vapor phase epitaxy (MOVPE) process. N2 was used as dilution and carrier gas throughout the growth process. The transmission electron microscopy (TEM) specimens were prepared by the standard mechanical grinding and ion-milling method. The final step of specimen preparation was done at low voltage and high milling angle with a Fischione ion mill to minimize the artifacts introduced during specimen preparation. ADF-STEM images were taken with a VG Microscopes HB603U 300-kV STEM fitted with a Nion aberration corrector ay Oak Ridge National Laboratory, giving an expected probe size in the range of 0.8 Å. It was observed that the widely cited IDB theoretical structure can exist in reality.