Limits
A pseudomorphic heterojunction bipolar transistor developed at the University of Illinois at Urbana-Champaign, built from indium phosphide and indium gallium arsenide and designed with compositionally graded collector, base and emitter, was demonstrated to cut off at a speed of 710 gigahertz.
Besides being record breakers in terms of speed, HBTs made of InP/InGaAs are ideal for monolithic optoelectronic integrated circuits. A PIN-type photo detector is formed by the base-collector-subcollector layers. The bandgap of InGaAs works well for detecting 1.55μm-wavelength infrared laser signals used in optical communication systems. Biasing the HBT to obtain an active device, a photo transistor with high internal gain is obtained. Among other HBT applications are mixed signal circuits such as analog-to-digital and digital-to-analog converters.
Read more about this topic: Heterojunction Bipolar Transistor
Famous quotes containing the word limits:
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—Terri Apter (20th century)
“The limits of prudence: one cannot jump out of a burning building gradually.”
—Mason Cooley (b. 1927)
“The great ship, Balayne, lay frozen in the sea.
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—Wallace Stevens (1879–1955)