EPITAXIAL-GROWTH OF COGA ON GAAS BY ORGANOMETALLIC CHEMICAL VAPOR-DEPOSITION

Epitaxial layers of CoGa have been grown successfully for the first time on (100)GaAs by organometallic chemical vapor deposition, using (eta5-C5H5)Co(CO)2 and Et3Ga as precursors. The composition of the intermetallic films is adjustable by control of the composition of the gas phase in such a way that no detectable lattice mismatch is observed between Ga-rich CoGa films and the GaAs substrate. However, the films deposited with an excess of Co exhibit a metastable alpha (fcc) structure corresponding to a Co1-xGax solid solution. These films are structurally incompatible with GaAs, and were also found to react with GaAs above 400-degrees-C to form CoAs. From gas phase compositions Et3Ga/CoCP(CO)2 greater-than-or-equal-to 5, the CoGa films have the cubic beta (CsCl) structure and grow epitaxially on (100)GaAs in the temperature range 260-300-degrees-C. The growth rate of these films has been investigated as a function of the deposition parameters. The Ga-rich beta-CoGa films are thermodynamically stable on GaAs at 500-degrees-C, which is the temperature used for GaAs epitaxial growth by this technique. This suggests that CoGa is a good candidate material for the fabrication of buried metal/CxaAs heterostructures by organometallic vapor-phase epitaxy.