An X-ray diffraction technique for analyzing basal-plane stacking faults in GaN

摘要

An X-ray diffraction (XRD) technique for analyzing basal-plane stacking faults (BSFs) is introduced and tested on GaN. The analysis considers the coexistence of multiple X-ray broadening terms including tilt, twist, limited coherence length, and inhomogeneous strain. By measuring and fitting a series of symmetric and asymmetric reflections planes, we deduce the lattice tilt, twist, lateral coherence length, and inhomogeneous strain contributions, which allow us to determine the existence of any additional broadening in m-plane GaN. We found that in fact certain ω-scans do have excess broadening and that their lattice plane dependence is similar to the functional dependence of BSFs derived for powder XRD (θ/20-scan). Applying such functional dependence allows us to estimate the BSF densities (I_1- and (I_2-type). The typical stacking fault density was estimated to be 1 × 10~6/cm in m-plane GaN grown on m-plane sapphire by MOCVD, while the relative densities of I_1- and I_2-type are sample dependent. In contrast to the m-plane GaN, stacking faults in GaN on c-plane sapphire do not contribute significantly to Bragg peak broadening and are below the detection limit.