Polarized laser light scattering applied to surface morphology characterization of epitaxial III–V semiconductor layers

Abstract

In this paper, we analyze typical morphologies of epitaxial III–V semiconductor layers by using a polarized laser light scattering technique. Crosshatched topographies, which are developed during heteroepitaxial growth, are studied. A sample with an intentionally high density of oval defects is also explored to establish how the laser light scattering pattern is affected by the presence of these defects, which are unavoidable in the epitaxial layers grown by molecular beam epitaxy. The former topographies produce a scattered light pattern that is highly anisotropic, with the intensity concentrated along two preferential directions; the latter defects give rise to a fairly isotropic pattern. Employing a perturbation-theoretical model, whose applicability and consistency are explicitly demonstrated by our results, the surface power spectral density is retrieved from the angle-resolved light scattering experimental data. For the samples exhibiting crosshatched topography, the scattering measurements provide information that allows us to model the roughness of the surface in terms of two quasi-one-dimensional, anisotropic components, and one two-dimensional, isotropic, long-range background. The root mean square heights and the typical lateral distances between ridges are obtained in quantitative agreement with the values extracted from the atomic force microscopy measurements. For the sample presenting oval defects, we consider their contribution to the surface power spectral density by means of a simple model of randomly distributed particles on a surface, and we compare the resulting power spectral density with typical behavior found in the literature for good-morphology GaAs layers. With the help of the ex situ information thus obtained, we also discuss the implementation of the light scattering technique for in situ monitoring during epitaxial growth.