We study and demonstrate a periodic array of "carbon nanotube-silicon" heterojunctions, its functioning as an infrared (IR) detector, and report on the first observation of near-to mid-IR photocurrent response in both the cooled and uncooled modes. The formation of carbon nanotubes in a periodic dense array, parallel to each other and perpendicular to the silicon substrate, offers a new promising IR material platform with spectral tunability and scalability in field size and absorbance as well as uniform electrical and optical accesses to each of the nanotubes. The spectral dependence of the photocurrent also allows for an estimate of the band gap of the nanotubes, which is found to be in good agreement with that determined from thermally activated dark conductivity measurements.

We present an infrared (IR) optical absorbance study of highly uniform nanotubes grown by chemical vapor deposition in the self-assembled porous matrix in alumina. For unambiguous IR spectral measurement, nanotubes were extracted from their growth template, purified, and evenly dispersed on a reflecting substrate. The findings, which are consistent with previous results from conduction studies, reveal that the nanotubes are semiconducting with a band gap of ∼100meV. This suggests the potential of nanotube arrays for IR electro-optical device applications.

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