Devices made from nanowires have already shown advantages over traditional planar light-emitting diodes (LEDs), such as more efficient light extraction. The high surface-to-volume ratio of nanowires also means that they are good candidates for sensing applications, where the optical properties of the nanowire can be drastically modified by changes in its environment. Moreover, high quality nanowires can be grown on cheap, routinely used substrates such as silicon, which means they could easily be used to fabricate commercial lighting devices.

The structures made by the Delft-Philips team are based on nanowire heterostructures made of the group III-IV semiconducting materials, indium-phosphide and indium-arsenide. The researchers begin by growing nanowires using a vapour-liquid-solid mode that allows structures with high crystalline quality and controlled diameters to be made. Next, they place a single nanowire, which is around 30 nm across and 4 μm long, on top of a silica substrate. Doping with hydrogen sulphide and diethyl-zinc along the wire axis then produces a pn junction in the nanowire.

The team found that their pn-doped device is a very small LED in which electron-hole recombination is restricted to a quantum dot-sized section of the wire. The device emits photons in the infrared range of wavelengths when a voltage is applied to it.

"The quantum dot sized segment could lead to an efficient electrically driven single photon source, useful for quantum cryptography and quantum information applications," team member Maarten van Kouwen told "We hope to be able to efficiently generate single photons on demand, as well as entangled photon pairs for such applications."

The Netherlands team says that it also aims to efficiently convert single electrons into single photons using its device. If this can be done coherently, it will allow a single electron spin to be converted into a given photon polarization, thus allowing a fast, reliable measurement of the single electron's spin. "The combined control of single electron spins and single photons would enable a number of experiments in the field of quantum information and could even provide the building blocks for devices such as quantum repeaters," explained team member Valery Zwiller.

The researchers reported their work in Nano Letters.