Silicon nanocrystal transistor shines

Most of the world's computer chips are made from silicon, a material that has excellent electrical properties. The optical properties of silicon wafers, however, leave much to be desired.

Researchers from the California Institute of Technology have mixed silicon nanocrystals with conventional bulk silicon to produce an all-silicon transistor that is capable of emitting light. The nanocrystals range from 2 to 4 nanometers in diameter, which is the span of 20 to 40 hydrogen atoms. In this form, silicon is better able to light up.

The nanocrystal field-effect light-emitting device (FELED) could be used to integrate light sources on computer chips. This would allow the light sources and control circuits of display and communications device to be fabricated together, making for a faster, cheaper manufacturing process.

The device is energy efficient; a prototype that generates several microwatts of optical power could be built in an area as small as a few hundred square microns, according to the researchers. A micron is one thousandth of a millimeter. The color light the transistor emits depends on the size of its nanocrystals.

The silicon nanocrystal field-effect transistor is similar to next-generation memory chips under development. The researchers' device, however, uses nanocrystals that are smaller and emit light, with a transparent gate electrode that allows light to escape.

The transistor is also similar to existing silicon nanocrystal light-emitting diodes. The researchers' device, however, provides power to the nanocrystals through an electric field generated around them when a voltage is applied to the gate electrode. The diodes require a direct current through the nanocrystals, which uses more power and creates more wear and tear.

Devices based on the researchers' prototype could be ready for commercial use within two to five years, according to the researchers. The work appeared in the January 23, 2005 issue of Nature Materials.