Metal-semiconductor-metal (MSM) photodetectors based on single-walled carbon nanotube film-silicon Schottky contacts

We fabricate and experimentally characterize metal-semiconductor-metal (MSM) photodetectors with CNT film Schottky electrodes on n-type and p-type silicon substrates. We extract a Schottky barrier height of ~0.45 eV and ~0.51 eV for CNT films on n-type and p-type Si respectively. The extracted barrier height corresponds to a CNT film workfunction of 4.5-4.7 eV, which is within the range of the previously reported workfunction values for individual CNTs. Furthermore, we find that while at temperatures above 240°K thermionic emission is the dominant transport mechanism, at lower temperatures tunneling begins to dominate. We also characterize the photoresponse of the CNT film-Si MSM photodetector by illuminating the samples with a 633 nm HeNe laser. We observe that while the photocurrent of the CNT film MSM devices is similar to that of the Ti/Au control samples at high biases, their lower dark current results in a higher photo-to-dark current ratio relative to the control devices. We explain these observations by comparing the two interfaces. This work opens up the possibility of integrating CNT films as transparent and conductive Schottky electrodes in conventional semiconductor electronic and optoelectronic devices.