RANGE OF DEFECT MORPHOLOGIES ON GAAS GROWN ON OFFCUT (001)GE SUBSTRATES

The quality of GaAs films grown on offcut (001) Ge substrates has been extensively investigated as a function of solid-source molecular beam epitaxy growth parameters using transmission electron microscopy. In the worst case, GaAs/Ge films may feature unexpectedly high threading dislocation densities and numerous anti-phase domains (APDs). The cond ensation of As point defects incorporated during low temperature (simi lar to 350 degrees C) GaAs co-evaporation is responsible for the nucle ation of dislocation loops with in-plane a/2[110] Burgers vectors. Sub sequent loop expansion produces an excess of threading dislocations an d an irregular misfit dislocation network. Regarding anti-phase disord er, As-initiated GaAs is sensitive to temperature-dependent Ge surface roughening effects, whereas Ga-initiated growth is highly sensitive t o background contamination levels. Nevertheless, APD-free GaAs/Ge film s initiated with either As or Ga were achieved by controlling the expo sure conditions and relying on an epitaxial Ge buffer annealed at high temperature to provide a clean, single domain surface for growth init iation. A model for APD coalescence is presented to explain observed v ariations in APD height.