Defect characterization in epitaxial ZnO/epi-GaN/Al 2O 3 heterostructures: transmission electron microscopy and triple-axis X-ray diffractometry

Abstract

Structural properties of epitaxial ZnO/epi-GaN/Al 2O 3 heterostructures have been studied by transmission electron microscopy and X-ray diffractometry for the first time. The majority of threading dislocations running along the growth direction of ZnO films are screw-type dislocations. At the interface region, a high density of dislocations located mainly on the basal plane was observed. These dislocations show intense dislocation reactions resulting in a rapid reduction of the dislocation density towards the upper region of the film. From X-ray rocking curve measurements, the full-width at half-maximum (FWHM) value of the (1 0 1) φ-scan is larger than that of the (0 0 2) ω-scan and increase with decreasing the ZnO film thickness. The increment of the width of the (1 0 1) φ-scan with decreasing the film thickness from 500 to 150 nm is much larger (0.13°) than that of the (0 0 2) ω-scan (0.04°). Different broadening in (1 0 1) φ-scan and (0 0 2) ω-scan rocking curves are explained in terms of the defect configuration as investigated by transmission electron microscopy (TEM).