Growth of III-V nitrides by molecular beam epitaxy (MBE) is being studied at NCSU using an r.f. nitrogen plasma source. GaN/SiC substrates consisting of ∼ 3 μm thick GaN buffer layers grown on 6H-SiC wafers by MOVPE at Cree Research Inc. are being used as substrates in the MBE film growth experiments. The MBE-grown GaN films exhibit excellent structural and optical properties--comparable to the best GaN films grown by MOVPE--as determined from photoluminescence, X-ray diffraction, and vertical-cross-section TEM micrographs. Mg and Si have been used as dopants for p-type and n-type layers, respectively. Al x Ga 1 - x N films (x ∼ 0.06-0.08) and Al x Ga 1 - x N/GaN multi-quantum-well structures have been grown which display good optical properties. Light-emitting diodes based on double-heterostructures of Al x Ga 1 - x N/GaN which emit violet light at ∼400 nm have also been demonstrated. Growth of GaN on LiGaO 2 substrates is also reported for comparison.