Defective carbon nanotube-silicon heterojunctions for photodetector and chemical sensor with improved responses

The direct growth and integration of defect-modulated carbon nanotubes (CNTs) on n-type silicon (Si) microstructures for high performance photodetectors and chemiresistive sensors is presented. By devising a Si microspring that is strained by the growth force of the CNTs, a vertical load from the restoring force of the microspring is perpendicularly applied against the growth direction of the CNTs. This vertical load induces the formation of defective structures in the CNTs while the CNT-Si heterojunctions are fabricated. Under the illumination of UV light, photogenerated carriers from both the CNTs and the Si can be separated at the CNT-Si heterojunctions and at the defects in the CNTs before recombination, which contributes to a high photoresponsivity of 262.3 mA W^-1 and an external quantum efficiency of 91.4%. Moreover, the adsorption of chemical species can be promoted by increasing the defects in the CNTs, thereby improving the sensing responsiveness toward ethanol and NO₂ vapors. Our simple and facile growth of defect-adjusted CNTs on conductive Si microstructures would be beneficial to the scalable, high throughput manufacturing of heterojunctioned devices with tunable properties and functionalities of the CNTs.