SURFACE SEGREGATION IN III-V ALLOYS

Recent measurements which demonstrate the occurrence of surface segregation during the MBE growth of III(a)III(b)-V ternary semiconductor alloys and III(a)-V/III(b)-V heterostructures are reviewed. This preferential segregation drives to the surface one of the third-column elements involved, to the expense of the other, within their common sublattice. In ternary alloys, the surface is found to be nearly binary, and a short-scale interface roughness is detected in heterostructures. For arsenides, the direction and extent of the segregation process follow the In > Ga greater-than-or-equal-to Al order. We discuss possible origins for the segregation process and the ability of standard segregation models to describe the results on ternary alloys and to predict composition profiles for any given heterostructure. These predictions are compared to recent measurements by high-resolution microscopy, ion scattering, photo-luminescence, or Raman scattering. Possible applications of the segregation process, and also remedies for avoiding it are finally discussed.