Nature Mater. http://doi.org/wx6 (2014)

Credit: NPG

Silicon has dominated the microelectronics revolution but, despite its potential, it has performed poorly as an emitter or detector at telecommunications wavelengths. Now, an international team from the UK, Russia, Czech Republic and the USA are tackling this problem by providing a way of engineering the bandgap energy of crystalline silicon. The team fabricated silicon optical fibres using a high-pressure chemical deposition method and then crystalized the core material using a continuous wave laser. This process induces substantial radial tensile stress, up to an estimated 6 GPa, which can be tuned by adjusting the laser irradiation time. The result is a convenient and straightforward way of modifying the optoelectronic properties of silicon. The maximum bandgap reduction observed was 0.5 eV — a reduction from the default value of 1.1 eV to a value of 0.6 eV. The absorption edge of the silicon therefore increased to more than 2 μm. The researchers predict that their method will be useful for other geometries or materials, constituting an important step towards the merging of optical and electronic functionalities within the same material platform.