A joint research team at the University of Toronto and the Karlsruhe Institute of Technology (KIT) has produced nanoscale silicon-based LEDs (SiLEDs). According to the researchers, these nanocrystals, consisting of only a few hundred to several thousand atoms, offer significant potential as highly efficient light emitters.
Standard LEDs are made from direct band gap materials, mainly gallium compounds. Up to now silicon has been regarded as unsuitable for use in LEDs because it can only generate light in the red and near-infrared regions. The researchers have now changed that view. Their extremely tiny silicon nanocrystals (1 to 3 nm in size) emit light, and the color of the light depends on the size of the crystal – the bigger the crystal, the longer the wavelength of the light.
The research team also developed a process to sort the nanocrystals by size. This enables them to make tiny LEDs with specific colors and to combine several LEDs to form multi-color arrays. However, they have not yet been able to generate white light. White light can theoretically be produced by mixing three primary colors, but so far they have not been able to produce a blue-light emitter.
The SiLEDs have surprisingly good long-term stability. This is a consequence of sorting the devices by size, which prevents potential short-circuits due to relatively large devices. In addition, the SiLEDs have high homogeneity of the light-emitting surfaces.