Researchers at the University of Illinois at Urbana-Champaign have developed the world's first light emitting transistor (LET).

Unlike conventional transistors, which include an electrical input port and an electrical output port, the new LET also has an infrared optical output port (see image at http://www.aip.org/mgr/png/2003/210.htm).

The LET is built of indium gallium phosphide and gallium arsenide, rather than the silicon and germanium used in many conventional transistors. Although the LET produces light in essentially the same way that light emitting diodes (LEDs) operate, the transistor can modulate light at much higher speeds.

To date, the researchers (N.Holonyak, Jr., blpayne@.uiuc.edu, 217-333-4149) have managed to modulate the optical LET output at a frequency of one megahertz, but much higher speeds are theoretically possible.

Although it's too early to predict the various applications for LETs, the hybrid device should help integrate electrical and optical circuitry designs with one convenient, high speed package. It is only fitting that the research team that developed the LET include the inventor of the first visible LED (Holonyak) and the developer of the world's fastest bipolar transistor (Feng).

(M. Feng et al., Applied Physics Letters, 5 January 2004)