Epitaxial growth of GaN film on (La,Sr)(Al,Ta)O3 (111) substrate by metalorganic chemical vapor deposition

GaN films were grown on (La0.29Sr0.71)(Al-0.65,Ta-0.35)O-3 (LSAT) (111) substrates, the lattice constant of which matched the 3 x 3 structure of GaN (0001) and the thermal expansion coefficient of which was close to that of GaN, by atmospheric metalorganic chemical vapor deposition. It was found that the surface of LSAT having a perovskite crystal structure was damaged in ambient of NH3 and TMG gas. However, the epitaxial growth of GaN film on the LSAT substrate was achieved by using an AlN blocking layer to prevent the damage by these gases. The crystallographic orientation was evaluated-from a phi-scan of 4-cycle X-ray diffraction to be GaN[1 (1) over bar 00] parallel to LSAT[1 (1) over bar0] rotating in plane by 30degrees against the expected orientation (GaN[2 (1) over bar(1) over bar0] parallel to LSAT[1 (1) over bar0]). The 30degrees rotation would be caused by the bond configuration of the surface of the LSAT substrate. The interface structure at the substrate and the threading dislocation in the films were also investigated using a cross-sectional transmission electron microscope.