Researchers at the University of Illinois have improved the performance of a Quantum Well Transistor and Laser. Their invention helps improve the performance of optical communications systems and can also be used to determine the noise figure of semiconductor optical amplifiers.
Overview of the Transistor Laser (from the website of Professor Feng)
Described in the Novermeber 15 issue of the journal Applied Physics Letters in 2004, Milton Feng, Nick Holonyak, postdoctoral research associate Gabriel Walter, and graduate research assistant Richard Chan demonstrated operation of the first heterojunction bipolar transistor laser by incorporating quantum well in the active region of light emitting transistor. Just as light emitting transistor, transistor laser was made of indium gallium phosphide, indium gallium arsenide, and gallium arsenide, but emitted coherent beam by stimulated emission, which differed from their previous device that only emitted incoherent photons. Despite their success, the device was not useful for practical purposes since it only operated at low temperatures about minus 75 in Celsius degrees. Within a year, though, the researchers finally fabricated a transistor laser operating at room temperature by using metal organic chemical vapor deposition (MOCVD), as reported in the September 26 issue of the same journal. At this time, the transistor laser had 14-layer structure including aluminium gallium arsenide optical confining layers and indium gallium arsenide quantum wells. The emitting cavity was 2,200nm wide, 0.85mm long, had continuous modes at 1,000nm. Plus, it had threshold current of 40mA and direct modulation of the laser at 3 GHz.