AlGaN-Based Photodetectors Grown by Gas Source Molecular Beam Epitaxy with Ammonia

AlGaN p-n junctions were used to fabricate photodetectors operating between 280 and 380 nm. Detector structures were grown on silicon and sapphire substrates by gas source molecular beam epitaxy with ammonia. Layers of n-Al_xGa_1-xN (0 ≤ x_AlN ≤ 0.08) were grown at a temperature of 800°C on a buffer layer of AlN. The p-type layers of Al_xGa_1-xN (0 ≤ x_AlN ≤ 0.08) were co-doped with Mg and oxygen. Hole concentrations as high as 2 × 10¹⁸ cm^-3 were measured by capacitance voltage profiling. In the p-Al_0.08Ga_0.92N layer we measured acceptor activation energy of 195 ± 10 meV. In a comparable layer of p-GaN, also co-doped with Mg and O, the acceptor activation energy was 130-165 meV. Low activation energies are attributed to successful co-doping. In mesa etched diodes we measured zero-bias leakage currents as low as 6 × 10^-13 A cm^-2.