External quantum efficiency of Pt/n-GaN Schottky diodes in the spectral range 5–500 nm

The external quantum efficiency in the spectral wavelength range 5–500 nm of a large active area Pt/n-type GaN Schottky photodiode that exhibits low reverse bias leakage current, is reported. The Schottky photodiodes were fabricated from n−/n+ epitaxial layers grown by low pressure metalorganic vapour phase epitaxy on single crystal c-plane sapphire. The current–voltage ( I – V ) characteristics of several 0.25 cm2 devices are presented together with the capacitance–voltage ( C – V ) characteristics of one of these devices. A leakage current as low as 14 pA at 0.5 V reverse bias is reported, for a 0.25 cm2 diode. The ultraviolet quantum efficiency measurements show that the diodes can be used as radiation hard detectors for the 5–365 nm spectral range without the use of visible blocking filters. A peak responsivity of 77.5 mA/W at 320 nm is reported for one of the fabricated devices, corresponding to a spectral detectivity, D * = 1.5 × 1 0 14 cm Hz 1 / 2 W - 1 . The average detectivity between 250 and 350 nm, for the same device, is reported to be D ¯ * = 1.3 × 1 0 14 cm Hz 1 / 2 W - 1 . The spatial responsivity uniformity variation was established, using H2 Lyman-α radiation, to be ±3% across the surface of a typical 0.25 cm2 diode.