A Korean team of scientists tune BP’s band gap to form a
superior conductor, allowing for the application to be mass produced for
electronic and optoelectronics devices
(August 14, 2015) The
research team operating out of Pohang University of Science and Technology
(POSTECH), affiliated with the Institute for Basic Science’s (IBS) Center for
Artificial Low Dimensional Electronic Systems (CALDES), reported a tunable band
gap in BP, effectively modifying the semiconducting material into a unique
state of matter with anisotropic dispersion. This research outcome potentially
allows for great flexibility in the design and optimization of electronic and
optoelectronic devices like solar panels and telecommunication lasers.
To truly understand the significance of the team’s findings,
it’s instrumental to understand the nature of two-dimensional (2-D) materials,
and for that one must go back to 2010 when the world of 2-D materials was
dominated by a simple thin sheet of carbon, a layered form of carbon atoms
constructed to resemble honeycomb, called graphene. Graphene was globally
heralded as a wonder-material thanks to the work of two British scientists who
won the Nobel Prize for Physics for their research on it.
Graphene is extremely thin and has remarkable attributes. It
is stronger than steel yet many times lighter, more conductive than copper and
more flexible than rubber. All these properties combined make it a tremendous
conductor of heat and electricity. A defect–free layer is also impermeable to
all atoms and molecules. This amalgamation makes it a terrifically attractive
material to apply to scientific developments in a wide variety of fields, such
as electronics, aerospace and sports. For all its dazzling promise there is
however a disadvantage; graphene has no band gap.
Phosphorene –
The natural successor to Graphene?
Stepping Stones to a Unique State
A material’s band gap is fundamental to determining its
electrical conductivity. Imagine two river crossings, one with tightly-packed
stepping-stones, and the other with large gaps between stones. The former is
far easier to traverse because a jump between two tightly-packed stones requires
less energy. A band gap is much the same; the smaller the gap the more
efficiently the current can move across the material and the stronger the
current.
Graphene has a band gap of zero in its natural state,
however, and so acts like a conductor; the semiconductor potential can’t be
realized because the conductivity can’t be shut off, even at low temperatures.
This obviously dilutes its appeal as a semiconductor, as shutting off
conductivity is a vital part of a semiconductor’s function.