Anisotropic surface roughness in molecular-beam epitaxy CdTe (211)B/Ge(211)

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 degrees 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 [(1) over bar 11] and [0 (1) over bar1] directions. For a substrate temperature of approximately 300 degrees 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.