TEM and SEM Studies of MOCVD-Grown GaP on Si

GaP and GaP/GaAsP epitaxial layers have been grown on Si substrates by metal-organic chemical vapor deposition (MOCVD). These layers were characterized by SEM and TEM plan-view and cross-sectional examination. At growth temperatures ranging from 600 degree C to 800 degree C, the initial stages of growth were dominated by three-dimensional nucleation. TEM studies showed that at high temperatures the nuclei were generally misoriented with respect to each other yielding, upon coalescence, polycrystalline layers. The growth of single-crystal layers was achieved by nucleating a 30-50 nm layer of GaP at 500 degree C, followed by annealing and continued growth at 750 degree C. The defect density in these structures was investigated as a function of various growth parameters and substrate conditions. A high density of structural defects was generated at the Si/GaP interface. The use of 2 degree off (100) Si substrates resulted in GaP layers free of antiphase domains. These results and their implications are discussed.