Dual mode UV/visible-IR gallium-nitride light detector

Abstract

Gallium-nitride (GaN) light detectors are sensitive to ultraviolet (UV) radiation below 365nm wavelength due to their wide bandgap – 3.4eV. However, the presence of impurities, especially surface traps, leads to slow relaxation rates and sub-bandgap response due to new energy levels. In the present work we offer utilizing these impurities to broad the spectral range up to the near-infrared (NIR) and modifying the surface of the photoresistors to enhance the response, the recovery time, and the repeatability by using several surface treatments such as plasma asher and the adsorption of organic molecules. The wide band response up to the NIR range was achieved by exciting the detector with a constant UV light intensity, resulting in a responsivity of 10–100A/W. We ascribe the high sensitivity to visible and NIR wavelengths to a gating amplification effect caused by trapped charges. Owing to the band bending of energy levels, a large depletion layer is created on the surface of the GaN layer, effectively separating the surface conductivity from the bulk. These properties make the detector sensitive to changes on the surface, thus making it ideal for biological and chemical uses as well as for broadband light detectors.