01 Dec 2005
Silicon riddled with tiny holes shows lasing action in the infrared.
Scientists in the US claim to have observed lasing from a nanostructured piece of silicon for the first time (Nature Materials advanced online edition). The news follows demonstrations earlier this year of silicon lasers that relied on either the Raman effect or rare-earth doping to achieve optical gain (see related stories).
The team from Brown University took an electronic grade silicon-on-insulator (SOI) wafer and used refractive ion etching and a nanopore mask to etch billions of tiny (60 nm wide) pores into its surface. They then cooled the wafer to cryogenic temperatures (10 K) and pumped it with up to 1.5 W of green light from an Argon Ion laser.
As the pump power was increased, Jimmy Xu and his colleagues Sylvain Cloutier and Pavel Kossyrev observed the telltale signs of lasing in the infrared -- optical gain followed by linewidth narrowing and the generation of a sharp emission peak at a wavelength of 1278 nm.
Although the exact mechanism behind the lasing is not clear, Xu’s team believes that it is due to the creation of A-centre defect states in the silicon. These defect energy states are located just below the conduction band and allow trapped electrons and free holes to recombine and emit light.
Currently, the emitted laser light is very weak, with an estimated output power of 30 nW and an external efficiency of about 0.0001% (1x10-6) and Xu says that his team did well to spot it. That said the researchers are confident that by optimizing the design it can be scaled to higher powers.
“Even though the external efficiency may seem to be very low, it is comparable to the optically pumped solid-state lasers in their early days and conventional noble gas lasers,” said the researchers in their paper. “Although only observed at cryogenic temperatures so far, we hope that this report will help generate broad interest and stimulate further investigations.”