PORTLAND, Ore. — The inventors of the transistor-laser —a transistor with
both optical and electrical outputs—claim it fits perfectly within the
semiconductor migration path to integrated optics. That may require that all the
electronics textbooks be rewritten to use TLs in circuits,
the inventors say, because the transistor-laser violated the concept of
conservation of charge, or Kirchhoff's Law.
"Similar to the way the transistor impacted today's electronic integrated
circuits, we expect the transistor laser to have a similarly major
impact--opening up new frontiers in electro-optical integrated circuits and for
optical interconnects," said professor Milton Feng, who performed the work with
fellow professor Nick Holonyak and doctoral candidate Han Wui Then.
The transistor laser has been known for about six years, but its inventors
only recently crafted a solution for its miss-match with traditional
circuit-theory. In particular, shortly after Georg Ohm defined the first
principle of circuit theory—Ohm's Law—Gustav Kirchhoff described the
still-universally-taught conservation-of-charge principle, called Kirchhoff's
Current Law (circa 1845): "At any junction in an electrical circuit, the sum of
currents flowing into that node is equal to the sum of currents flowing out of
that node." But with a transistor laser some of the current goes to creating the
laser beam—mixing charge conservation with energy conservation.
"New text books will be needed to incorporate the transistor laser," said
Feng. "Kirchhoff's Current Law should be redefined as Kirchhoff 's Current and
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.
Next the team plans to construct a set of transistor-laser building blocks for use in integrated circuit design.
Funding was provided by the U.S. Army Research Office.