RESEARCH GROUP: Brian Thoms, Ananta Acharya
RESEARCH
The research goal of this program is to obtain a fundamental understanding
of the physics and chemistry of semiconductor surfaces, especially Group
III-nitride semiconductors. Wide bandgap semiconductors (WBS) such as gallium
nitride and aluminum nitride offer many potential electronics and optics
applications. For example, the use of WBS in solar-blind detectors, blue lasers
and LEDs, and optical windows and coatings are among the motivations for the
recent work in this area. Besides their large bandgap, these materials often
possess other useful properties such as hardness, corrosion resistance, high
thermal conductivity, negative electron affinity, and high carrier mobilities
which make them useful in applications such as high power, high frequency
devices, field emitters, heat sinks, and protective coatings. Ironically, it is
the extreme properties of these materials which also make their use in
technological applications challenging.
Indium nitride, while it has a much narrower band gap, has promising
transport characteristics. In
particular, it has a low effective electron mass, resulting in a high mobility
and high saturation velocity of the electrons.
It has become a promising material for applications in high frequency,
high speed, & high-electron-mobility transistors, chemical and biological sensors, transparent conducting window material
for heterojunction solar cells, thermoelectric devices and terahertz radiation
devices.
The Group-III nitrides are already in
wide use in many optoelectronic applications (e.g. green LEDs in traffic
lights, blue lasers in Blu-ray disc players).
Most of the current applications involve GaN with small amounts of In
and/or Al substituted for
LABORATORY
Experiments on structure, bonding, chemical reactivity, and electronic
properties of wide bandgap semiconductor surfaces are conducted in the
Department's surface science laboratory. The laboratory is equipped with an
ultra-high vacuum surface science apparatus with capabilities for sample
preparation and surface modification as well as multiple surface sensitive
techniques. The ultra-high vacuum system is comprised of three interconnected
vacuum chambers in which samples can be transferred without exposure to the
ambient environment. In each chamber, the sample can be positioned, heated to
1300 K, or cooled to near liquid nitrogen temperatures. One of these chambers
is dedicated to sample preparation (surface cleaning) by heating in a
controlled environment, ion bombardment, or exposure to a flux of excited
species (evaporated metal or hydrogen atoms). The remaining two chambers are
used for surface characterization using various techniques including
temperature programmed desorption (TPD), low energy electron diffraction
(LEED), Auger electron spectroscopy (AES), energy loss spectroscopy (ELS), and
high resolution electron energy loss spectroscopy (HREELS). LEED images are
photographed off of a fluorescent screen using a digital camera. All other data
are acquired under computer control using GPIB, CAMAC, or serial interfaces to
microcomputers.
SELECTED PUBLICATIONS
Desorption of hydrogen from
R. P. Bhatta, B. D. Thoms, M. Alevli, and N. Dietz
Surface Science 602. 1428 (2008).
Surface Electron Accumulation in Indium Nitride Layers
Grown by High Pressure Chemical Vapor Deposition.
R. P. Bhatta, B. D. Thoms, M. Alevli, and N. Dietz
Surface Science 601. L120 (2007).
Carrier concentration and surface electron accumulation
in indium nitride layers grown by high pressure chemical vapor deposition.
R. P. Bhatta, B. D. Thoms, A. Weerasekera, A. G. U.
Perera, M. Alevli, and N. Dietz,
J. Vac. Sci. Technol. A 25, 967 (2007).
Surface Structure, Composition, and Polarity of Indium
Nitride Grown by High Pressure Chemical Vapor Deposition.
R. P. Bhatta, B. D. Thoms, M. Alevli, V. Woods, and N.
Dietz.
Applied Physics Letters 88, 122112 (2006).
HREELS of H/GaN(0001): Evidence for Ga Termination.
V. J. Bellitto, B. D. Thoms, D. D. Koleske, A. E. Wickenden, and R. L.
Henry.
Surface Science 430, 80 (1999).
Electronic Structure of H/GaN(0001): An ELS Study of Ga-H Formation.
V. J. Bellitto, B. D. Thoms, D. D. Koleske, A. E. Wickenden, and R. L.
Henry.
Physical Review B 60, 4816 (1999).
Efficient Electron Stimulated Desorption of Hydrogen from GaN(0001).
V. J. Bellitto, B. D. Thoms, D. D. Koleske, A. E. Wickenden, and R. L.
Henry.
Physical Review B 60, 4821 (1999).
Desorption of hydrogen from GaN(0001) observed by HREELS and ELS.
V. J. Bellitto, Y. Yang, B. D. Thoms, D. D. Koleske, A. E. Wickenden, and R.
L. Henry.
Surface Science Letters 442, L1019 (1999).
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