Illinois research team fabricates transistor laser
A GaAs-based transistor that also acts as a laser has been demonstrated by researchers at the University of Illinois at Urbana-Champaign (UIUC).
"By incorporating quantum wells into the active region of a light-emitting transistor, we have enhanced the electrical and optical properties, making possible stimulated emission and transistor laser operation," explained Nick Holonyak, a member of the research team.
The so-called heterojunction bipolar light-emitting transistor (HBLET) operates in quasicontinuous mode (88% duty cycle) at a temperature of 200K.
Infra-red emission is generated through the recombination of electrons and holes, which form the base current, in the device s InGaAs quantum well. At the onset of lasing, which occurs at around 958 nm, the optical output power increases but the transistor s gain falls, according to co-worker Milton Feng.
The epitaxial wafer processes required for HBLET fabrication were developed at US firm Epiworks. "One of the main hurdles was developing a new growth process because no one has really tried to grow a device like this," remarked EpiWorks president, Quesnell Hartmann.
According to the UIUC scientists, development of HBLETs could extend the modulation bandwidth for a semiconductor light source from 20 GHz to over 100 GHz. Alternatively, transistor lasers used as optical interconnects could facilitate faster signal processing, higher-speed devices and large-capacity seamless communications, as well as a new generation of higher performance electrical and optical integrated circuits.
Holonyak acknowledges that the work is still in its infancy: "There is much to learn, including how to separate and optimize the transistor laser output between electrical signals and light signals."
More information concerning the research group s findings can be found in the November 15 issue of Applied Physics Letters.
• Nick Holonyak is also to receive the 2004 MRS Von Hippel award for "his many contributions to research and development in the field of semiconductors, not least for the first development of semiconductor lasers in the visible portion of the optical spectrum".
