Measuring the depth profiles of strain/composition in AlGaN-graded layer by high-resolution x-ray diffraction

Abstract

Here, we demonstrate X-ray fitting through kinematical simulations of the intensity profiles of symmetric reflections for epitaxial compositionally graded layers of AlGaN grown by molecular beam epitaxy pseudomorphically on [0001]-oriented GaN substrates. These detailed simulations depict obvious differences between changes in thickness, maximum concentration, and concentration profile of the graded layers. Through comparison of these simulations with as-grown samples, we can reliably determine these parameters, most important of which are the profiles of the concentration and strain which determine much of the electrical properties of the film. In addition to learning about these parameters for the characterization of thin film properties, these fitting techniques create opportunities to calibrate growth rates and control composition profiles of AlGaN layers with a single growth rather than multiple growths as has been done traditionally.

High-resolution X-ray diffraction analysis of strain distribution in GaN nanowires on Si(111) substrate

“…The deviations of the out-of-plane lattice parameter from the bulk value along the NW's height appear as variations in the length of the scattering vector q at which the Bragg's condition is satisfied. According to the geometry conditions of the scattering process for symmetric reflections [12], the length of q  =  k in  −  k out (where k in and k out are the incident and scattered wave vectors, respectively) is related to the incidence angle θ by:…”

Investigation of the Structural and Optical Properties of Compositionally V‐Graded Strained InxGa1–xN Layers

“…This is accompanied by the broad set of oscillations to smaller angles. These again are signatures of the V‐graded layers . In addition, their sharpness indicates the high quality of the interfaces and the absence of strain relaxation.…”

“…However, here the calculations were applied for the structure consisting of a compositionally graded InGaN layer on the GaN substrate with the generalization that the regions of different compositions in the growth direction represent the regions of coherent scattering. The intensity of the scattered X‐rays by the InGaN layer was calculated according to Equation , which sums together the scattered amplitudes from all the unit cells in the GaN substrate and the InGaN layer where F i is the structure factor of a cell at depth t i , is the length of the scattering vector, θ is the scattering angle, and λ is the wavelength.…”

High-resolution X-ray diffraction analysis of strain distribution in GaN nanowires on Si(111) substrate

“…The deviations of the out-of-plane lattice parameter from the bulk value along the NW's height appear as variations in the length of the scattering vector q at which the Bragg's condition is satisfied. According to the geometry conditions of the scattering process for symmetric reflections [12], the length of q = k in − k out (where k in and k out are the incident and scattered wave vectors, respectively) is related to the incidence angle θ by:…”