Due to the perceived impact of silicon photonics, numerous efforts have been devoted to develop silicon (Si) as a viable optical material. One important field that would benefit from an efficient Si-based light source is in display devices for light emission in visible spectrum.

While there has been successful demonstration of a full visible colour spectrum emission through photo-excitation of Si quantum dots embedded in a nitride matrix with diameter range ~1.3 to 2.9nm, there are few reports of electroluminescence (EL) in Si-based materials. There are reports on visible colour EL covering the red, green and blue but all are limited to a single-colour emission or with wavelength ranges that are overlapping. Recently, a switchable two-colour emission has been demonstrated but it is due to electronic transitions in extrinsic Eu dopants (Eu3+ and Eu2+).

Researchers from IME’s Nano-Electronics and Photonics Group have developed an electrically excited Si-based light source that can emit two colours simultaneously. The inset in the diagram shows the perceived violet emission from a biased device, taken with a digital camera under bright light conditions. The perceived violet colour is a result of simultaneous emission of both red and blue colour. The emission is bright enough to be observed by the naked eye.

The red emission is believed to be related to quantum confinement effects from within the nanoscale silicon structure while the blue emission is thought to originate from some radiative “defect” sites (e.g. neutral oxygen vacancy sites). While the operating power for this device is still very high and not yet suitable for commercialisation, this work demonstrates the potential for the realisation of a full colour display using a Si-based light source.