Anisotropic Surface Roughness in Molecular-Beam Epitaxy CdTe (211)B/Ge(211)

Abstract

We characterize the surface of molecular-beam epitaxy (MBE)-grown CdTe(211)B/Ge(211) by atomic-force microscopy (AFM), optical interference microscopy, and generalized ellipsometry (GE). We find that, for substrate temperatures above 300°C, the surface is rough and hazy; the AFM root-mean-square roughness is of the order of 150 A. It appears from GE that the optical response is anisotropic, the principal axes of anisotropy being along the \( [\overline{1} 11] \) and \( [0\overline{1} 1] \) directions. For a substrate temperature of approximately 300°C, the surface is smooth and mirror-like and the AFM roughness is as low as 45 A. The sample is still anisotropic, even though the magnitude of the cross-polarized reflection coefficients are very small in this case. It appears that the anisotropy originates from the surface roughness, not the bulk.