The Metamorphosis of the
Transistor into a Laser
Milton Feng and Nick Holonyak Jr.
The transistor put us on the path to semiconductor electronics
research. It led to the integrated circuit, optoelectronics, light-detecting devices, diode lasers, LEDs, and now further to
the transistor laser—a true laser and three-terminal photonic
transistor active element.
Courtesy of Milton Feng
rguably the most important transistor ever made was the Bardeen and Brattain
point-contact transistor, which came in 1947. It was the original bipolar semi-
conductor triode (i.e., +/– charge conduction, the positive hole as important
as the negative electron). It was the device that started it all, the prototype that ultimately
doomed the vacuum tube. It led to the integrated circuit and a vast new branch of electronics
that made large-scale computers possible.
Eventually, because of +/– bipolarity and electron-hole recombination, it also led to the
diode laser and the LED. In short, the first transistor ultimately changed the world’s economies and history. The point-contact transistor was primitive but ingenious—it included just
the required bare minimum, a small crude “slab” of germanium (Ge). It was simply an n-type
“base” crystal with an ordinary Ohmic current contact attached to the bottom (terminal #1, B),
with an input metal point-contact minority carrier (hole) emitter (terminal #2, E) on the top
surface, and nearby an output metal point-contact “collector” (terminal #3, C).
Indeed it was just enough—a “base” crystal and three contacts (EBC)—to reveal the
three-terminal low-impedance input/high-impedance output “transfer-resistor” idea. The
transistor was a radically new bipolar active amplifying and switching element. When Bardeen and Brattain demonstrated their device, which in the beginning was not known and not
named, it was totally new, not previously anticipated by anyone. It emerged in physics like a
strange mushroom popping out of the ground in a forest.
For what it was and what it revealed as a progenitor, the point-contact transistor of Bardeen
and Brattain outranks all other transistors. Because of it, the hole in a real working sense was
elevated to the importance of the electron. It ceased to be, as many had believed, just a mysterious construct of quantum physics. It was real, and it was put to work. Of further consequence,
the electron and hole were connected across the gap by the photon (ph, hn Eg), pointing
clearly at the possibility of sooner or later a new electronics based on the electron, hole and photon—all three. After the transistor, it was bound to happen.
What many people may not know or appreciate, however, is that the very existence of the
electron-hole bipolarity (–/+) set the path to today’s diode laser, LED, optoelectronics … and
now the transistor laser.
March 2011 | 45