Photodetectors Based on Chemical Vapor Deposition or Liquid Processed Multi-Wall Carbon Nanotubes

Carbon nanotubes (CNTs) have attracted great interest for applications due to their unique mechanical, electronic and optoelectronic properties. The advantages of the multiple wall carbon nanotubes for optoelectronic devices like photodetectors and photodiodes are the large effective photo-collector surface as well as the possibility to tune the band gap and absorbance by controlling the growth parameters. In this work, we demonstrate two types of hybrid Multi-Wall CNTs/Si3N4/n-Si photodetectors based on ordered (produced with Chemical Vapor Deposition – CVD) and solution processed MWCNTs and evaluate their performance in UV and visual spectrum (275nm, 655nm). Device parameters were obtained by comparison of I-V characteristics to Schottky barrier models and C-V characteristics to standard MIS capacitor models. The role of silicon nitride layer was also examined by comparing devices with different nitride layer thickness. Focusing on the UV part of the spectrum the solution processed device was photosensitive in the voltage range 3V to 6V giving its best performance (External Quantum Efficiency - E.Q.E. 80%@275nm) at 5V and illumination of 5μW. The CVD processed device showed lower EQE for the same bias voltage range. Both devices showed a low performance in optical part of the spectrum compared to the corresponding one in the UV part of the spectrum. The mean optical responsivity values obtained at the UV part of the spectrum in both cases indicate that hybrid MWCNT/Si3N4/n-Si systems have a potential use in UV photodetector applications. In particular, solution processed devices may pave the way for cheap production of UV sensor systems.