Substrate-orientation dependence of GaN single-crystal films grown by metalorganic vapor-phase epitaxy

Gallium-nitride single crystals were grown on (0001)- and (011̄2)-oriented sapphire substrates by metalorganic vapor-phase epitaxy. Smooth-surfaced layers with fine ridgelike facets can be obtained on the (011̄2) sapphire. They have lower carrier concentrations than the layers on the (0001) sapphire. Deep centers responsible for blue (∼425 nm) and yellow (∼560 nm) emissions from undoped layers are reduced on the (011̄2) substrates, as compared with the (0001) substrates. On the other hand, the layers on the (0001) sapphire have better crystallinity and higher Zn-incorporation efficiency than those on the (011̄2) sapphire. Growth kinetics of GaN layers are discussed by developing a tentative model.