Abstract: Pt/n?GaN Schottky barrier diodes are disclosed that are particularly suited to serve as ultra-violet sensors operating at wavelengths below 200 nm. The Pt/n?GaN Schottky barrier diodes have very large active areas, up to 1 cm2, which exhibit extremely low leakage current at low reverse biases. Very large area Pt/n?GaN Schottky diodes of sizes 0.25 cm2 and 1 cm2 have been fabricated from n?/n+GaN epitaxial layers grown by vapor phase epitaxy on single crystal c-plane sapphire, which showed leakage currents of 14 pA and 2.7 nA, respectively for the 0.25cm2 and 1 cm2 diodes both configured at a 0.5V reverse bias.