External quantum efficiency of Pt/n-GaN Schottky diodes in the spectral range 5-500Â 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*=1.5×1014cmHz1/2W-1. The average detectivity between 250 and 350 nm, for the same device, is reported to be D¯*=1.3×1014cmHz1/2W-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.