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 Ga.  The growth of high quality materials with higher indium content has proven difficult as has the growth of high quality InN.  Our present work takes advantage of high quality InN being grown within the department by the Dietz Research Group.

 

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 InN(000-1) observed by HREELS.

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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