Defects in Atomically Thin Semiconductor Emit Single Photons

Optical micrograph of electrically contacted tungsten diselenide. (Source: Chakraborty et al. / NPG)

Optical micrograph of electrically contacted tungsten diselenide. (Source: Chakraborty et al. / NPG)

Defects on an atomically thin semiconductor can produce light-emitting quantum dots that serve as a source of single photons and could be useful for the integration of quantum photonics with solid-state electronics – a combination known as “integrated photonics”.
Quantum dots are artificially engineered or naturally occurring defects in solids that are being studied for a wide range of applications. Nick Vamivakas, assistant professor of optics at the University of Rochester adds that atomically thin, 2D materials, such as graphene, have also generated interest among scientists who want to explore their potential for optoelectronics. However, until now, optically active quantum dots have not been observed in 2D materials.
The researchers showed how tungsten diselenide (WSe2) can be fashioned into an atomically thin semiconductor that serves as a platform for solid-state quantum dots. Perhaps most importantly the defects that create the dots do not inhibit the electrical or optical performance of the semiconductor and they can be controlled by applying electric and magnetic fields.
Vamivakas explains that the brightness of the quantum dot emission can be controlled by applying the voltage. The next step is to use voltage to “tune the color” of the emitted photons, which can make it possible to integrate these quantum dots with nanophotonic devices.
A key advantage is how much easier it is to create quantum dots in atomically thin tungsten diselenide compared to producing quantum dots in more traditional materials like indium arsenide.
The researchers take two of these atomically thin sheets and lay one over the other one. At the point where they overlap, a quantum dot is created. The overlap creates a defect in the otherwise smooth 2D sheet of semiconductor material. The extremely thin semiconductors are much easier to integrate with other electronics. The quantum dots in tungsten diselenide also possess an intrinsic quantum degree of freedom – the electron spin. This is a desirable property as the spin can both act as a store of quantum information as well as provide a probe of the local quantum dot environment. (Source: University of Rochester)

References: Ch. Chakraborty et al.: Voltage-controlled quantum light from an atomically thin semiconductor, Nat. Nanotechnol., online 4 May 2015; DOI: 10.1038/nnano.2015.79

Links: University of Rochester

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