MARY ELLEN ZVANUT, Professor

(205) 934-6661, mezvanut@.uab.edu

Spectroscopic and Electrical Studies of

Electronic and Optical Materials

The research in our lab involves studies of materials used in microelectronic, optical, and magnetic applications. In the area of electronics, present and ongoing materials of interest are SiC and GaN.  They are studied in order to deduce their potential in high speed and/or high power electronic applications. Specifically, point defects in SiC wafers are examined using electron paramagnetic resonance spectrosocopy (EPR) so that we may understand their role in achieving semi-insulating material.  GaN, the semiconductor which will form the basis of future lighting applications, contains several point defects critical to its application in both light emitting diodes and high power devices.  We address the chemical kinetics of these defects to assess the response of the material to varying environments.

            In collaboration with Physics colleague, Dr. Sergey Mirov, we study the structure of defects in potentially laser-active media.  At present, the work focuses on the role of Cr in achieving lasing in various II-VI and ternary compounds.

            In collaboration with colleagues throughout the US, we are studying complex oxides, materials which can be mated to well-established electronics substrates such as SiC and produce multi-functional devices.  Magnetic, optical, and electronic operations are to be collected on one chip.  With this goal, we are studying the Fe impurity in LiNbO3 and well as magnetic impurities in SiC and GaN.

The experimental techniques used in this work, electron paramagnetic resonance (EPR) spectroscopy and a wide variety of electrical measurements, are designed to address the low concentrations of isolated defects and impurities typical of technological-grade electronic material.  In addition, the low temperature EPR measurements are key to understanding the physical structure of the impurities responsible for the properties of semi-insulating SiC,and other materials.

Dr. Jami Dashdorj (left) mounts a sample for an EPR measurement while Ms. Sarah Thomas (right) sets up for data acquisition.

 

 

 

 

 

 

 

 

 

 

 

Instrumentation:  

The EPR equipment, located in the Solid State laboratory includes:

  • Bruker Model EMX 9.6Ghz EPR Spectrometer
  • Air Products closed cycle helium refrigerator
  • Oxford Instruments ESR900 Cryostat System
  • Microphotonics SingleWavelength Ellipsometer
  • Southbay Diamond Wheel and polishing equipment

 The equipment in the materials fabrication and analysis laboratory includes:

  • Keithley Model 82 Simultaneous CV System
  • AC Conductance Instrumentation: 1 Hz to 1 MHz
  • Bias Temperature Stress Instrumentation
  • MMR Joule Thompson Refrigerator and high temperature stage
  • TENCOR Alpha-Step 500 Surface profilometer
  • Ultra-dry Annealing Furnace and Moisture monitor
  • High Temperature Oxidation furnace
  • Metal Deposition System
  • Southbay wire saw

The laboratories, research, and students are supported by the Office of Naval Research and the National Science Foundation.

Collaborations:

  • The Naval Research Laboratory
  • Air Force Research Laboratory, Wright Patterson AFB
  • Auburn University
  • University of Pittsburgh
  • University of Alabama at Tuscaloosa
  • General Electric Global Research

Recent Publications:

  1. J. Dashdorj, M.E. Zvanut and J.G. Harrison, “Measurements of optical cross sections of carbon vacancy in 4H-SiC by time-dependent photo-electron paramagnetic resonance”, J. Appl. Phys. 104, 113707 (2008).

 

  1. M.E. Zvanut, S. Jeddy, and E. Towett, G.M. Janowski, C. Brooks and D. Schlom, “An annealing study of an oxygen vacancy related defect in SrTiO­3 substrates”, J. Appl. Phys. 104, 064122 (2008).

 

2.      Wonwoo Lee and M. E. Zvanut, “A study of deep defect levels in semi-insulating SiC using optical admittance spectroscopy”, J. Electron. Materials 36, 623 (2007).

 

  1. W. C. Mitchel, W. D. Mitchell, G. Landis, H. E. Smith, Wonwoo Lee, and M. E. Zvanut,  “Vanadium donor and acceptor levels in semi-insulating 4H- and 6H-SiC”, J. Appl. Phys. 101, 013707 (2007)

 

4.      M.E. Zvanut, Wonwoo Lee, W.C. Mitchel, W.D. Mitchel, W.D. Mitchell, and G. Landis, “The acceptor level for vanadium in 4H and 6H SiC”, Physica B 376-377, 346 (2006).

 

5.      M.E. Zvanut, Haiyan Wang, Mpumelelo Richards, and V. V. Konovalov, “Observation of a spin one native defect in as-grown high purity semi-insulating 4H SiC”, J. Appl. Phys. 97, 123509 (2005).

 

  1. D. M. Matlock, M. E. Zvanut, Haiyan Wang, Jeffrey R. DiMaio, R.F. Davis, J.E. Van Nostrand, R. L. Henry, Daniel Koleske and Alma Wickenden, “The effects of oxygen, nitrogen, and hydrogen annealing on Mg acceptors in GaN as monitored by electron paramagnetic resonance spectroscopy”, Journal of Electronic Materials 34, 34 (2005).

 

Conference Proceedings

 

  1. M. E. Zvanut, G. Ngetich, H. J. Chung, A. Y. Polyakov, M. Skowronski, E. Glaser, and N. Garces, “Defect level of the carbon vacancy carbon antisite pair center in SI 4H SiC”, Mat. Sci. Forum  600-603, 385 (2009).

 

  1. E.R. Glaser, N.Y. Garces, W.E. Carlos, M.E. Zvanut, B. Magnusson, D.M. Hansen, G. Chung, and M.J. Loboda, “Infrared PL Signatures of n-type Bulk SiC Substrates with Nitrogen Impurity Concentration Between 1016 and 1017 cm-3”, Mat. Sci. Forum  600-603, 449 (2009).

 

3.      J. Dashdorj and M.E. Zvanut, “Study of chromium impurities in SrTiO3 by photo-electron paramagnetic resonance spectroscopy”, edited by J.F. Scott, V. Gopalan, M. Okuyama, and M. Bibes (Mater. Res. Soc. Symp. Proc. Volume 1034E, Warrendale, PA, 2008), 1034-K10-19.

 

  1. M. E. Zvanut, G. Ngetich, H. J. Chung, A. Y. Polyakov, and M. Skowronski, “A study of vacancies and vacancy pair defects in 4H SiC grown by halide chemical vapor deposition”, J. Mat. Sci: Mat. in Electronics 19, 678 (2008).

 

5.      M.E. Zvanut and J. van Tol, “Nitrogen-related point defect in 4H and 6H SiC”, Physica B 401-402, 73-76 (2007).

 

6.      Shehnaz Jeddy, Mary Ellen Zvanut, Brian Einstein Lassiter, Gregg M. Janowski and Leonard J. Brillson “Themal Stability of defects in substrates of multiferroic materials”, in Ferroelectrics and Multiferroics, edited by V. Gopalan, J-P. Maria, M. Fiebig, C-W. Nan (Mater. Res. Soc. Symp. Proc. 966E, Warrendale, PA, 2007), 0966-T05-04.

 

7.        M. E. Zvanut, H. J. Chung, A. Y. Polyakov, and M. Skowronski, “Point defects in 4H SiC grown by Halide Chemical Vapor Deposition”, Mat. Sci. Forum 556-557, 473 (2007).