AlGaN-based resonant cavity-enhanced UV-photodetectors

Back-illuminated AlGaN-based UV-RCE-MSM-PDs, in which the light is incident from the sapphire substrate are discussed. To obtain high responsivity in RCE-PDs, high reflectivity for the mirror opposite from the incident side is necessary The back-illumination enabled us to employ dielectric SiO₂/ZrO₂ DBR mirrors with high reflection capability as the backside reflector. The devices were fabricated on sapphires by improved rf-plasma molecular beam epitaxy (rf-MBE). High-temperature grown AlN nucleation layers were grown on sapphires to control the crystal polarity of (Al)GaN layers into Ga- or Al-polar, followed by Al_0.14Ga_0.86N (34.4 nm)/AlN (40.5 nm) DBR mirrors, Al_0.14Ga_0.86N cladding layer and GaN absorption layer. In this study, Al_0.14Ga_0.86N was synthesized with AIN/GaN superlattice quasi-ternary. On grown crystals, Pd (80 nm)/Au (100 nm) interdigitated Schottky electrodes and then SiO₂/ZrO₂ DBR were deposited to complete the device process. The detection responsivity was evaluated with normal incidence of light.