Characterization of surface roughness anisotropy on mismatched InAIAs/lnP heterostructures

Abstract

We have studied surface roughness on mismatched In0.65Al0.35As epilayers of various thicknesses on (001) InP. The sample set spans the entire range from coherently strained to completely relaxed epilayers. As characterization tools, we have used atomic force microscopy (AFM), laser light scattering (LLS), and variable azimuthal angle ellipsometry (VAAE). AFM reveals that the surfaces are covered by densely packed ellipsoidal islands elongated along the [1-10] direction. The island size increases with layer thickness. Island anisotropy and the root mean square of the surface roughness increase with increasing thickness but decrease upon full lattice relaxation. LLS intensity displays a prominent azimuthal dependence that correlates well with the two-dimensional power spectrum of the surface topography, as predicted by theory. VAAE reveals a sinusoidal dependence of the ellipsometric parameter Δ on azimuthal angle. The amplitude of A correlates well with the short wavelength anisotropy of the surface power spectrum. Our work suggests that LLS and VAAE are fast, nondestructive, sensitive techniques for characterization of surface roughness in mismatched III-V heterostructures.