Chemical sensitivity of convergent beam electron diffraction on the stoichiometry of GaN

Abstract

III-V nitride thin film growth has attracted considerable attention because it now seems feasible to engineer semiconductor band gaps between 2.1 and 6.2 eV. One of the challenges coming with this development is related to the fact that structural perfection seems not to correlate directly with optical properties such as the emission of blue-green or UV light in GaN. In order to better understand this material High Resolution Transmission Electron Microscopy (HREM) and Convergent Beam Electron Diffraction (CBED) experiments were used to study structural defects in GaN thin films. Experiments were performed with a Topcon 002B and ARM operating at 200 and 800 KeV, respectively, and were guided by image simulations. Results of parallel luminescence studies will be published elsewhere.Plan-view micrographs of GaN grown on the (0001) basal plane of A12O3 with a lattice mismatch of 14% show small angle grain boundaries which divide the layer into large subgrains of about 800 nm diameter. Other defects visible in the plan-view micrographs are threading dislocations and planar defects lying parallel to the {1010} planes of the GaN.