ACS Nano http://doi.org/wvw (2014)

The energy required by an electric charge to be excited from the valence band of a semiconductor to its conduction band usually determines the working spectral range of solar cells and photodetectors based on that material. However, intraband transitions — excitations between energy levels within the same band — have also been used to detect photons in the infrared range. Zhiyou Deng and colleagues have now prepared efficient infrared photodetectors by using intraband transitions in n-doped HgSe colloidal quantum dots. Precise control of the doping level is essential to minimize the noise current and to increase the device sensitivity to infrared radiation. The right doping is obtained for a range of sizes of HgSe quantum dots, which are used to realize prototypes that work efficiently at a temperature of 80 K and can still detect radiation at room temperature. The researchers expect that improved operation at room temperature will be possible by further controlling at the synthesis stage the surface composition and the ligands between the particles.