Ga-polar GaN film grown by MOVPE on cleaved ScAlMgO₄ (0001) substrate with millimeter-scale wide terraces

Cleaved ScAlMgO₄ (SCAM) substrates with small lattice mismatch of 1.8% to GaN were used for metalorganic vapor phase epitaxial (MOVPE) growth of GaN. A single crystalline GaN film with a flat surface was obtained on a cleaved substrate without peeling off of the film, which is contrast to the growth on ZnO substrate with comparably small lattice mismatch to GaN. Polarity of the film was proven to be Ga polarity and an interface model was proposed based on the topmost surface structure of the cleaved SCAM. The effect of substrate-cleaning and growth conditions on the surface morphology, crystallographic orientation relationship with the substrate, threading dislocation densities, small residual strains, and small background carrier density of GaN have been studied. To discuss the residual strains, thermal expansion coefficient of SCAM has also been measured.