Light amplification in silicon

Ubiquitous in integrated circuitry, bulk silicon is notoriously reluctant to emit light. The road to ever-faster circuits, however, leads to optoelectronics…the use of optical rather than electronic components such as switches. Silicon can emit some light, but only from nanoscale structures in which quantum effects come into play. Most semiconductor lasers are instead made from so-called III–V materials, like gallium arsenide or indium phosphide. Now, physicists in Italy (at INFM and the universities of Trento and Catania have demonstrated optical gain in silicon nanocrystals. They embedded a dense array of 3-nm silicon quantum dots…at a concentration exceeding 10¹⁹ cm⁻³…in a silicon oxide matrix. The material exhibited both stimulated emission of light and an optical gain comparable to that from III–V semiconductors. The researchers attribute the gain to radiative surface states at the abundant nanocrystal–oxide interfaces. The next step for the scientists is to try to make the light coherent, an essential property for optoelectronic applications. (L. Pavesi et al., Nature 408 , 440, 2000 http://dx.doi.org/10.1038/35044012 .)