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. 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 (200-1000nm). 

    The principal objective - and challenge -  of this work is to realize novel  photodetectors based on dense arrays  of MWCNTs deposited directly on a Silicon substrate,  To this end it is necessary to match the high temperature (~800 0C)  carbon nanotube formation process with the other processes required for device fabrication. Since a Fe catalyst (Ferrocene) is required during the growth stage, the presence of a diffusion barrier between the MWCNT layer and Si is mandatory and to this end we used Si3N4. In sequence it will be provided evidence that the  silicon nitride interlayer (a) acts as a metal diffusion barrier (b) its resistivity decreases due to the the presence of metal atoms (reduces to 10⁹ Ohm.cm compared to  1014 Ohm.cm when non-contaminated) thus contributing to charge transport through trap assisted tunneling and (c) due to its large bandgap (5.2eV) renders the device sensitive in the UV region. It will be discussed that the MWCNT layer acts as an effective  photon absorber and electron-hole generation takes place in the substrate including the silicon nitride layer. 

The basic device and some meaningful variations including additional layers are electrically and optically tested and compared. The overall results suggest that all devices had a satisfactory performance in the visual part of the spectrum and that the basic structure had the better performance as a UV detector (EQE 90% @ 275nm@ 7V).

1. Kyriakis, A. et al. A UV photodetector based on ordered free standing MWCNT. in Journal of Instrumentation (2020). doi:10.1088/1748-0221/15/01/C01015
2. Filatzikioti, A. et al. Carbon nanotube Schottky type photodetectors for UV applications. Solid State Electron. 151, 27–35 (2019).