Chemical Electronic Coupling and the InAs Two-Dimensional Electron Gas (2DEG): Highly Sensitive and Selective Sensing of Surface- Based Biomolecule Interactions

The origin of surface donors yielding the InAs surface-potential confined
two-dimensional electron gas (2DEG) remains unknown, but is believed to be defect-based
and therefore related to surface reconstruction, strain, and/or native defects associated with
surface processes such as oxidation. We show that the surface oxide (either engineered or
"native") can be used as a reagent in surface-based chemical interactions modifying surface
molecular attachment, both conformation and coverage, in a concentration-dependent fashion.
These molecular interactions can be, in turn, "sensed" through changes in the 2DEG density and
mobility.

Using x-ray photoelectron spectroscopy (XPS) and Hall measurements, we show that changes in
the oxide chemistry resulting from surface DNA and protein interactions are sensitively reflected
in changes in the 2DEG density and mobility. As an electronic sensor, biomolecule (DNA/protein)
adsorption can be measured down to fM concentrations with dynamic range of greater than
four orders of magnitude. DNA hybridization can also be electronically sensed and differentiated
from non-specific binding in the fM concentration range. These results, realized with a planar
device implementation, show performance equal to that realized in a nanowire-based device.

At higher concentrations (µM), adsorbed single-stranded DNA (ssDNA) average conformation
and coverage is highly dependent on the evolving oxide chemistry that changes from In-oxide
(In2O3)- to As-oxide (As2O3/As2O5)-rich or lean as a result of specific DNA ligand interactions.
These changes are readily "read-out" in 2DEG density and mobility changes. We find that amine
groups bind to the As/As oxide and that As oxide-richness can lead to the creation of dense
ssDNA brushes associated with changes in the
hydrogen bonding network as determined with FTIR.
Dr. April S. Brown is the John Cocke
Professor of Electrical and Computer Engineering at
Duke University. She received her Ph.D. degree from
Cornell University in 1985. She worked at the Hughes
Research Laboratories (now HRL LLC) in Malibu, Ca.
from 1986-1993, and spent one year at the Army
Research Office in the Physics Division (1988). She was
at the Georgia Institute of Technology (1994-2002) as
the Pettit Professor in Microelectronics where she also
served as Associate Dean in the College of Engineering
and as Executive Assistant to the President. She joined
Duke University as Professor and Chair in July 2002.
She is currently Sr. Associate Dean for Research in
the Pratt School of Engineering. Professor Brown's
research has focused on epitaxial growth of InP – and
GaN-based semiconductors, material characterization
and microelectronic devices.

Professor Brown is Fellow of IEEE and the American
Physical Society. She received the Paul Rappaport
Award from the IEEE Electron Device Society and has
also been a Distinguished Lecturer of this Society. She
received the Georgia Tech Women's Leadership Award
in 2001.