CHARACTERIZATION OF SURFACE-ROUGHNESS ANISOTROPY ON MISMATCHED INALASINP HETEROSTRUCTURES/

We have studied surface roughness on mismatched In0.65Al0.35As epilaye rs of various thicknesses on (001) InP. The sample set spans the entir e range from coherently strained to completely relaxed epilayers. As c haracterization tools, we have used atomic force microscopy (AFM), las er light scattering (LLS), and variable azimuthal angle ellipsometry ( VAAE). AFM reveals that the surfaces are covered by densely packed ell ipsoidal islands elongated along the [1 (1) over bar 0] direction. The island size increases with layer thickness. Island anisotropy the roo t mean square of the surface roughness increase with increasing thickn ess but decrease upon full lattice relaxation. LLS intensity displays a prominent azimuthal dependence that correlates well with the two-dim ensional power spectrum of the surface topography, as predicted by the ory. VAAE reveals a sinusoidal dependence of the ellipsometric paramet er Delta on azimuthal angle. The amplitude of Delta correlates well wi th the short wavelength anisotropy of the surface power spectrum. Our work suggests that LLS and VAAE are fast, nondestructive, sensitive te chniques for characterization of surface roughness in mismatched III-V heterostructures.