Low-dark-current large-area narrow-band photodetector using InGaN/GaN layers on sapphire

A metal-semiconductor-metal structure was fabricated on a 20-nm-thick InGaN layer, and showed a responsivity of over 0.1 A/W to the wavelength of 400 nm at a bias of I V. The photocurrent was almost linear to the power of the incident light in three decades. The Schottky interdigital electrodes kept the dark current to less than 100 pA at 10 V despite its large detecting area of 1 mm(2). The device showed fast responses on the order of 10 ns to optical impulses from a 407 nm laser diode. Biasing at 1 V or lower is effective in suppressing the sensitivity in the wavelength range shorter than 350 run when illuminated from the substrate side through a 2-mu m-thick GaN layer, resulting in a narrow-band detector for the 400 run band.