Efficient readout for carbon nanotube (CNT)-based IR detectors

By forming a Schottky barrier with the contact metal, a semiconducting CNT based Schottky photodiode is formed at the CNT-metal contact The photogenerated electron-hole pairs within the depletion region of the Schottky barrier are separated by an external electrical field or the built-in field, producing a photocurrent. How to efficiently read this photocurrent signal out is an essential problem for the photodetectors. Since a semiconducting CNT normally forms a Schottky barrier at each CNT-electrode contact, two Schottky photodiodes are reversely connected and their photocurrents will cancel each other, which makes it difficult to measure the overall photocurrent. With different materials as the contact electrodes, the asymmetric structure enlarged the difference between the two CNT-metal contacts. Hence the measurable photocurrent is also enlarged. Furthermore, since the CNT Schottky barrier is determined by the metal work function and the Fermi level of the CNT, the Schottky barrier is able to be adjusted by controlling the Fermi level of the CNT with a gate electrode. In this way, the photocurrent can be optimized to a maximum value by varying the gate voltage. CNT based infrared detectors with different structures were fabricated and tested. Experimental results showed that the asymmetric structure and the gate controlled CNT based photodiode could significantly improve the performance of CNT based infrared detectors.