A UV photodetector based on ordered free standing MWCNT

Multiple wall carbon nanotubes (MWCNT) present advantages for optoelectronic applications such as the large effective photo-collector surface as well as the possibility to tune their band gap and absorbance through the growth parameters. The combination of CNTs with conventional semiconductors and metals to form a device presents technological challenges because of the high temperatures required for the production of CNTs and the catalysts used (e.g. Fe). These conditions may result in structural modifications of the substrate specially when the CNT formation temperature approaches the formation temperatures of other layers or even cause metal migration. The use of ordered free-standing MWCNTs for photodevice presents advantages, since they have a tunable absorbance depending on their height while their dense ordering results in a large effective area sensor. Additionally, the bandgap depends on their thickness, thus it is tunable by changing the formation conditions. In this work, we demonstrate a hybrid MWCNT/Si3N4/n-Si photodetector based on ordered MWCNTs and evaluate its performance in the UV, visual and near IR spectrum (200-1000 nm). Depending on the application the absorbing nanotube layer can be made thick enough (e.g. several millimeters) to enhance radiation absorption and electron-hole pair generation. The best result obtained so far as a UV detector is a 90% Equivalent Quantum Efficiency@ 275 nm for a 20 mu m CNT layer thickness.