Large and tunable photothermoelectric effect in single-layer MoS2.

We study the photoresponse of single-layer MoS(2) field-effect transistors by scanning photocurrent microscopy. We find that, unlike in many other semiconductors, the photocurrent generation in single-layer MoS(2) is dominated by the photothermoelectric effect and not by the separation of photoexcited electron-hole pairs across the Schottky barriers at the MoS(2)/electrode interfaces. We observe a large value for the Seebeck coefficient for single-layer MoS(2) that by an external electric field can be tuned between -4 × 10(2) and -1 × 10(5) µV K(-1). This large and tunable Seebeck coefficient of the single-layer MoS(2) paves the way to new applications of this material such as on-chip thermopower generation and waste thermal energy harvesting.

Probing optical transitions in individual carbon nanotubes using polarized photocurrent spectroscopy.

Carbon nanotubes show vast potential to be used as building blocks for photodetection applications. However, measurements of fundamental optical properties, such as the absorption coefficient and the dielectric constant, have not been accurately performed on a single pristine carbon nanotube. Here we show polarization-dependent photocurrent spectroscopy, performed on a p-n junction in a single suspended semiconducting carbon nanotube. We observe an enhanced absorption in the carbon nanotube optical resonances, and an external quantum efficiency of 12.3% and 8.7% was deduced for the E11 and E22 transitions, respectively. By studying the polarization dependence of the photocurrent, a dielectric constant of 3.6 ± 0.2 was experimentally determined for this semiconducting carbon nanotube.

Fast and efficient photodetection in nanoscale quantum-dot junctions.

We report on a photodetector in which colloidal quantum dots directly bridge nanometer-spaced electrodes. Unlike in conventional quantum-dot thin film photodetectors, charge mobility no longer plays a role in our quantum-dot junctions as charge extraction requires only two individual tunnel events. We find an efficient photoconductive gain mechanism with external quantum efficiencies of 38 electrons-per-photon in combination with response times faster than 300 ns. This compact device-architecture may open up new routes for improved photodetector performance in which efficiency and bandwidth do not go at the cost of one another.