Red/green/blue selective phototransistors with a hybrid structure of quantum-dots and an oxide semiconductor

Abstract

Color-selective phototransistors have been developed using a hybrid film of quantum-dots (QDs) and an oxide semiconductor. The zinc oxide (ZnO) phototransistor with QDs with a 2.96 eV band gap showed a photocurrent when illuminated by 450 nm light. The device with QDs with a 2.28 eV band gap started to show a photocurrent under 520 nm light, and the device with QDs with a 1.95 eV band gap showed a photocurrent under light with a wavelength of 635 nm. The photocurrent with low-energy photons, such as visible light, originated when small band-gap QDs absorbed and converted visible light into photoelectrons, and the transparent wide band-gap ZnO supplied a conductive channel in the conduction band to allow the photocurrent to flow through the device. Based on those results, we developed a color-selective phototransistor that can separate red, green, and blue light using a hybrid structure of ZnO and multilayer QDs. The device showed photoresponsivity values of 0.032, 0.053, and 0.26 mA/W to red, green, and blue light, respectively, which are different enough to distinguish the color of the visible light. Therefore, we fabricated and characterized a photogating inverter to convert the color of visible light into an electrical voltage signal. Our results show that the hybrid film of ZnO and QDs could be a feasible way to develop a highly transparent, full-color image sensor.