The potential of wide-band-gap III-V nitrides as solar-blind ultraviolet sensors and light emitters has prompted an increasing amount of work recently, including the fabrication of the first UV sensors from as-deposited single crystal GaN. We have used high resolution transmission electron microscopy (TEM) to study the microstructure of two novel developments of wideband-gap III-V nitrides: the growth of ultra-short period GaN/AlN superlattices (digital alloys); and the incorporation of SiC layers into AlxGa1-xN structures. By varying the relative periods in a GaN/AIN superlattice, it should bepossible to tailor the band gap of the composite to lie between the elemental values of 365nm for GaN and 200nm for AIN. The group IV semiconductor, SiC, has a close lattice match (< 3%) to AlxGa1-xN forgrowth on the basal plane. Demonstration of epitaxial growth for AlxGa1-xN/SiC multilayers could enable an extension of direct band-gap material towards the visible.The superlattice samples were grown by low-pressure metalorganic chemical-vapor deposition (MOCVD)using a unique switched atomic-layer-epitaxy (SALE) procedure (as first used by Dapkus et al. for GaAs). GaN was grown on the basal-plane sapphire substrates above a thin AlN layer, which has been foundto maximize the crystalline quality of the GaN film.