Photonic crystal with a HfO2 defect to improve performance of carbon nanotube based photodetectors

It has been demonstrated that carbon nanotube (CNT) acts as a promising functional material to effectively detect infrared signals due to the unique properties arose from its novel geometry. However, the performance of CNT based photodetectors is limited by low fill factor owing to their small photon absorption area. In order to address this problem, a photonic cavity, using photonic crystal with a point defect made of HfO₂, was fabricated on top of the CNT photodetectors in order to enhance the local photon density. By drilling holes, with size of the scale of light wavelengths, in the parylene slab, the periodic change of reflective index forms photonic crystal. Replacing one of the holes with HfO₂ as a point defect, most of the light will be trapped in this defect. A photonic crystal was designed to concentrate the infrared light with 1064 nm wavelength, and 91% of the light can be confined into the HfO₂ defect. The fabrication process of this photonic crystal is introduced, and photocurrents of a CNT based photodetector are compared under the circumstance of without and with photonic crystal. It is found that the photocurrent is enhanced about 4 times after the fabrication of photonic cavity.