Friday, May 14, 2010

Transistor-laser breaks Kirchhoff's Law, rewrites textbooks #Semiconductor #Laser #Microchip

Transistor-lasers could enable on-chip optics by providing both an electrical and an optical output, but the old-school textbooks will have to be rewritten to accomodate the new device. Look for transistor lasers in commercial chips within five years. R.C.J.

The EE inventors of the transistor-laser (TL) —a transistor with both optical and electrical outputs—claim it fits perfectly within the semiconductor migration path to integrated optics. Unfortunately, all the electronics textbooks will have to be rewritten to use TLs in circuits, inventors say, because the transistor-laser breaks the time-worn concept of conservation of charge—Kirchhoff's Law, which has to be rewritten to accommodate the transistor laser developed by Milton Feng and Nick Holonyak Jr. at the University of Illinois. The researchers have created an equivalent circuit to their quantum-well-based transistor-laser that accurately models the charging and discharging mechanisms in the transistor-laser's base, where lasing occurs. As a consequence, TL circuits can now be studied in computer simulations that analyze both frequency and time-domain performance. The researchers have verified their algorithm on a prototype transistor-laser cast in III-V materials. The emitting layer was composed of indium gallium arsenide quantum wells sandwiched inside a p-type base. An emitting cavity of 2.2 microns wide and 0.85 millimeter long emitted at 1.0 micron wavelength, had a threshold current of 40mA and enabled direct modulation of the laser at 3 GHz...
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