Analysis of the modified williamson-hall plot of non-polar a-plane GaN films

Abstract

We report on the Williamson-Hall (W-H) plot analysis of non-polar a-plane GaN (a-GaN) films for a better understanding of the anisotropic peak broadening with X-ray in-beam direction. The full width at half maximum (FWHM) values of the symmetric reflections of the X-ray rocking curves at different angles phi for the a-GaN film clearly show the anisotropic behavior of its structural property. A modified W-H plot analysis of the symmetric and reflections shows that the mosaic blocks are highly elongated along the c-axis direction. The W-H plots of the peak widths from the n th order reflections in the asymmetric geometry with an angle chi of 30° (ϕ = 0°) can provide quite useful information on the microstructural state of a-GaN films. We found that a coherent scattering length of ∼285 nm could be obtained for an a-GaN film with high crystalline quality. We note that the coherent scattering lengths obtained from W-H analyses can significantly underestimate the density of basal-plane stacking faults for nonpolar a-GaN films.