GaN photodetectors prepared on silicon and sapphire substrates

GaN ultraviolet metal-semiconductor-metal photodetectors (PDs) grown on Si and sapphire substrates were prepared. It was found that dark currents of PDs prepared on Si substrates were much smaller than that prepared on sapphire substrate. With an incident wavelength of 355 nm and an applied bias of 5 V, it was found that peak responsivities were 0.016 and 0.074 A/W while rejection ratios (i.e. 355 nm : 425 nm) were 2100 and 420 for u-GaN on Si and u-GaN on sapphire, respectively. The corresponding D* were 1.73times10¹⁰ and 1.08times10⁹ cmHz^0.5W^-1, respectively.