CHAMPAIGN, Ill. —
By depositing thin films of silicon nanoparticles
on silicon substrates, researchers at the University
of Illinois at Urbana-Champaign have fabricated a
photodetector sensitive to ultraviolet light. Silicon-based
ultraviolet sensors could prove very handy in military,
security and commercial applications.
"Silicon is the
most common semiconductor, but it has not been useful
for detecting ultraviolet light until now," said
Munir Nayfeh, a professor of physics at Illinois and
a researcher at the Beckman Institute for Advanced
Science and Technology. "Ultraviolet light is
usually absorbed by silicon and converted into heat,
but we found a way to make silicon devices that absorb
ultraviolet light and produce electrical current instead."
As will be reported
in the August issue of the journal Photonics Technology
Letters, the technique behind silicon sensing of ultraviolet
light is compatible with conventional integrated circuit
technology. Conveniently, both the sensor and the
computer could be incorporated on the same chip.
To create their ultraviolet-based
photodetectors, Nayfeh, graduate students Satish Rao,
Adam Smith and Joel Therrien, and undergraduate student
Osama Nayfeh begin with nanoparticles dispensed from
silicon wafers using electrochemical etching. The
nanoparticles are about 1 billionth of a meter in
diameter and contain about 30 silicon atoms.
The researchers then
deposit a thin film of the nanoparticles in a hole
etched into the surface of another silicon wafer using
standard lithographic techniques. Small conductive
pads of gold complete the assembly. Electricity flows
when ultraviolet light strikes the nanoparticles.
light efficiently couples to the nanoparticles and
produces electron-hole pairs," said Nayfeh, who
also is a researcher at the university’s Center for
Nanoscale Science and Technology. "Contrary to
what occurs in bulk silicon, the electron-hole pairs
do not appreciably recombine by non-radiative processes.
Strong quantum confinement allows for charge separation
nanoparticles with conventional silicon wafers could
offer the best of both material systems, Nayfeh said.
"Placing a thin layer of nanoparticles on the
front of a silicon solar cell, for example, could
improve the cell’s efficiency and its lifetime."
include ultraviolet-based detectors for missile-warning
systems and airborne biological agents, industrial
flame sensors and suntan monitors.
The National Science
Foundation; the state of Illinois; the Grainger Foundation;
and the Technology Research, Education, and Commercialization
Center funded the work. TRECC is managed by the National
Center for Supercomputing Applications and funded
by a grant from the Office of Naval Research. The
researchers have applied for a patent.
E. Kloeppel, Physical Sciences Editor