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.
World’s fastest transistor
In 2003, Milton Feng and his graduate students Walid Hafez and Jie-Wei Lai broke the record for the world’s fastest transistor. Their device, made of indium phosphide and indium gallium arsenide with 25nm-thick base and 75nm-thick collector, marked a frequency of 509 GHz, which was 57 GHz faster than the previous record. In 2005, they were successful to fabricate a device at Micro and Nanotechnology Laboratory to break their own record, reaching 604 GHz. In the following year, he and his other graduate student William Snodgrass fabricated a device with 12.5nm-thick base, operating at 765 GHz at room temperature and 845 GHz at minus 55 Celsius degrees.
Light emitting transistor
Reported in the January 5 issue of the journal Applied Physics Letters in 2004, Milton Feng and Nick Holonyak, the inventor of the first practical light emitting diode (LED) and the first semiconductor laser to operate in the visible spectrum, made the world’s first light emitting transistor. This hybrid device, fabricated by Feng’s graduate student Walid Hafez, had one electrical input and two outputs (electrical output and optical output) and operated at a frequency of 1 MHz. The device was made of indium gallium phosphide, indium gallium arsenide, and gallium arsenide, and emitted infrared photons from the base layer.