A III-V nitride, e.g., GaN, substrate including a (0001) surface offcut from the <0001> direction predominantly toward a direction selected from the group consisting of <1010> and <1120> directions, at an offcut angle in a range that is from about 0.2 to about 10 degrees, wherein the surface has a RMS roughness measured by 50x50 [mu]m<2> AFM scan that is less than 1 nm, and a dislocation density that is less than 3E6 cm<-2>. The substrate may be formed by offcut slicing of a corresponding boule or wafer blank, by offcut lapping or growth of the substrate body on a corresponding vicinal heteroepitaxial substrate, e.g., of offcut sapphire. The substrate is usefully employed for homoepitaxial deposition in the fabrication of III-V nitride-based microelectronic and opto-electronic devices.