Characterization of AlGaN-based metal–semiconductor solar-blind UV photodiodes with IrO2 Schottky contacts

Intrinsically solar-blind ultraviolet (UV) AlGaN-based Schottky photodiodes were fabricated using Iridium oxide (IrO2) as the Schottky barrier material. The Ir Schottky contacts were annealed at 700 °C under O2 ambient and the photodiodes characterized with an optoelectronic system. The main parameters extracted from I–V measurements were an average ideality factor of 1.38, a Schottky barrier height of 1.52 eV, a reverse leakage current density at −1 V bias of 5.2 nA/cm2 and series resistance of 250Ω. After spectral characterization, it was found that annealing, alone, of the Ir contact to form the more UV transmissive IrO2 does not always improve the responsivity. The deposition of a Au probe contact on the IrO2 contact increased the responsivity from 40 mA/W to 52 mA/W at 275 nm with respect to the annealed Ir contact. However, the ideality factor degraded to 1.57, Schottky barrier height lowered to 1.19 eV, reverse leakage current density increased to 49 nA/cm2 and series resistance decreased to 100Ω with the addition of the Au contact. The radiation hardness of AlGaN was also confirmed after studying the effects of 5.4 MeV He-ion irradiation using 241Am for a total fluence of 3×10133×1013 cm−2.