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

GaN films were grown on (La_0.29,Sr_0.71)(Al_0.65,Ta_0.35)O ₃ (LSAT) (111) substrates, the lattice constant of which matched the 3 × 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[11̄00] ∥ LSAT[1 1̄0] rotating in plane by 30° against the expected orientation (GaN[21̄1̄0] ∥ LSAT[11̄0]). The 30° 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.