Characterization of the ScAlMgO_4 cleaving layer by X-ray crystal truncation rod scattering

摘要

ScAlMgO4-easily cleaved in c-plane-forms a natural superlattice structure of a ScO2 layer and two Al0.5Mg0.5O layers stacking along c-axis. ScAlMgO4 is one of the RAMO(4)-type layered multicomponent oxides and a promising lattice-matching substrate material for InGaN and ZnO. Identification of the topmost layer and the surface atomic structure of the cleaved ScAlMgO4 (0001) are investigated by the X-ray crystal truncation rod scattering method. It is confirmed that ScAlMgO4 is cleaved between the two Al0.5Mg0.5O layers. The two parts separated at this inter-layer are inversion symmetric to each other and without surface charge. This prevents parallelplate-capacitor-like electrostatic force during the cleavage. Two different mechanisms are proposed for the two types of cleavage caused by the impact of a wedge and by the in-plane stress due to an overgrown thick GaN film. It is also revealed that about 10%-20% of the topmost O atoms are desorbed during a surface cleaning at 600 degrees C in ultra-high vacuum. Surface observations using reflection high-energy electron diffraction are possible only after the high-temperature cleaning because the electrical conduction caused by the oxygen deficiency prevents the charge-up of the insulating sample. Published by AIP Publishing.