Homewood’s team implanted boron ions into a piece of silicon to form a potential junction – the basis of all LEDs. But the ions also displace silicon atoms into a ring around the boron ion. These ‘dislocation loops’ create local electric fields that trap electrons and positive holes, which then recombine and emit radiation in the near-infrared part of the spectrum. This is very close to the wavelengths – 1.3 µm and 1.5 µm – used in fibre optic communications. The team is currently developing a wavelength-tunable version of the LED.

It is difficult to make silicon emit light because of its electronic structure. But a light-emitting device made from silicon could easily be incorporated into the mass production techniques used in consumer electronics, unlike, say, gallium arsenide. Components that could send and receive light signals instead of electrons could communicate literally at the speed of light. Such components are crucial for further miniaturization: as electronic circuits become ever smaller, electrons spend proportionately more time travelling between components – and these connections are fast approaching their maximum efficiency.

Coupled with an optical cavity, the silicon LED could ultimately form the basis of a silicon laser. The cavity would collect and amplify the light, and then emit it as a coherent beam. “The LED is a useful device in itself”, Homewood told PhysicsWeb, “but we are also confident that it is the route to a silicon laser – and we are working on that now”. Silicon lasers have been the goal of many recent attempts to coax light from silicon, but have been dogged by low efficiencies at room temperature.