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

Abstract

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 cm 2 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 cm 2 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 H 2 Lyman-α radiation, to be ±3% across the surface of a typical 0.25 cm 2 diode.