THE ROLE OF THE V III RATIO IN THE GROWTH AND STRUCTURAL-PROPERTIES OF METALORGANIC VAPOR-PHASE EPITAXY GAAS/GE HETEROSTRUCTURES/

GaAs epitaxial layers have been grown on (001) 6 degrees off-oriented toward (110) Ge substrates by metalorganic vapor phase epitaxy. In ord er to study the influence of V/III ratio on the growth mechanisms and the structural properties of the layers, the input flow of arsine was changed over a wide range of values, while keeping constant all other experimental settings. Optical microscopy in the Nomarski contrast mod e, x-ray topography and high resolution diffractometry, transmission e lectron microscopy and Rutherford backscattering have been used to inv estigate the epilayers. It has been found that the growth rate increas es and the surface morphology worsens with increasing V/III ratio. The abruptness of the layer-substrate interface has also been found to st rongly depend on the V/III ratio, the best results being obtained unde r Ga-rich conditions. The main structural defects within the layers ar e stacking faults and misfit dislocations. Layers grown under As-rich conditions only contain stacking faults, probably originated by a grow th island coalescence mechanism, whereas layers grown under Ga-rich co nditions contain both misfit dislocations and stacking faults generate d by dissociation of threading segments of interfacial dislocations. I n spite of the different defects, the strain relaxation has been found to follow the same trend irrespective of the V/III ratio. Finally, th e relaxation has been found to start at a thickness exceeding the theo retical critical value.