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:
“The great ship, Balayne, lay frozen in the sea.
The one-foot stars were couriers of its death
To the wild limits of its habitation.
These were not tepid stars of torpid places
But bravest at midnight and in lonely spaces,
They looked back at Hans’ look with savage faces.”
—Wallace Stevens (1879–1955)
“Europe has what we do not have yet, a sense of the mysterious and inexorable limits of life, a sense, in a word, of tragedy. And we have what they sorely need: a sense of life’s possibilities.”
—James Baldwin (1924–1987)
“Yet shall he mount, and keep his distant way
Beyond the limits of a vulgar fate:
Beneath the Good how far—but far above the Great.”
—Thomas Gray (1716–1771)