Properties of single-walled carbon nanotube film/Si heterojunctions fabricated in situ

Single-walled carbon nanotube (SWCNT) film/Si heterojunctions were obtained by depositing SWCNT films directly on a Si substrate by the floating catalyst chemical vapor deposition. The single-walled nature of the nanotubes was proven and confirmed by Raman and infrared spectroscopy, respectively. An additional ethanol post-growth treatment improved the properties of the heterojunctions by increasing densification of SWCNTs and decreasing their sheet resistance. Peaks positions of radial breathing mode obtained from the Raman mapping analysis demonstrated a random chirality (varying between armchair and zigzag) of tube structures and their very narrow diameter distribution, centered at ≈ 1.06 nm. This latter result was also confirmed by infrared spectroscopy. Properties of SWCNT/Si heterojunctions, such as ideality factor, Schottky barrier height, series resistance, SWCNT film work function and density of interface states are presented. To obtain the last two parameters by a self-consistent method, the intermediate nanolayer of silicon oxide between the SWCNT film and Si is considered. Impact of interface states and the native silicon oxide at the SWCNT/Si interface on the properties of heterojunctions is also discussed. Finally, such basic optoelectronic figures of merit as the responsivity, detectivity, and external quantum efficiency in the visible spectral range were determined and found to be comparable to the best reported for other SWCNT-based photodetectors.