MARY ELLEN ZVANUT, Associate 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, GaN epitaxial layers, and laser active materials.

 

Right: The electronics materials group, including its youngest member, examines the complicated lattice structure of 4H-SiC.

 

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
  • Georgia Institute of Technology
  • University of Pittsburgh
  • University of Alabama at Tuscaloosa
  • Dow Corning Corporation

Recent Publications:

  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).
  2. M.E. Zvanut, “Electron Paramagnetic Resonance Studies of electronic-grade SiC substrates”, J. Phys.: Condens. Matter 16, R1341-R1367 (2004).

 

  1. M.E. Zvanut, V.V. Konovalov, Haiyan Wang, W. C. Mitchel, W.D. Mitchel, and G. Landis, “Defect levels and types of point defects in high purity and vanadium-doped semi-insulating 4H SiC”, J. Appl. Phys. 96, 5484-5489 (2004).

 

  1. M.E. Zvanut, “Electron Paramagnetic Resonance Characterization of SiC” in SiC Power Materials, Devices and Applications”, Ch. 7, Zhe Chuan Feng, ed. (Springer-Verlag, Berlin, 2004), p. 277.

 

5.      W. C. Mitchel, William D. Mitchell, M. E. Zvanut, and G. Landis, “High Temperature Hall Effect Measurements of Semi-Insulating 4H-SiC Substrates”, Solid State Electronics 48, 1693-1697 (2004).

 

6.      M. B. Johnson , S. B. Mirov , V. Fedorov , M. E. Zvanut , J. G. Harrison , V. V. Badikov and G. S. Shevirdyaeva, “Absorption and Photoluminescence studies of CdGa2S4:Cr”, Optics Communications 233, 403-410 (2004).

 

7.      M.E. Zvanut, V. V. Konovalov, W.C. Mitchel, and W.D. Mitchell, “Optically induced transitions among point defects in high purity and vanadium-doped semi-insulating 4H SiC”, in Silicon Carbide and Related Materials, edited by R. Madar, J. Camassel, and E. Blanquet (Trans. Tech. Publicatons Ltd, Switzerland, 2004) or Materials Science Forum 457-460, 501 (2004).

 

8.      M.E. Zvanut, D. M. Matlock, R. L. Henry, Daniel Koleske, and Alma Wickenden, “Thermal activation of Mg-doped GaN as monitored by electron paramagnetic resonance spectroscopy”, J. Appl. Phys. 95, 1884-1887 (2004).

 

9.      Valery V. Konovalov, Mary-Ellen Zvanut, J. van Tol, “240 GHz EPR Studies of Intrinsic Defects in As-Grown 4H SiC”, Physical Rev B 68,012102 (2003).

 

10.  D. Alvarez, V.V. Konovalov, and M.E. Zvanut, “Effects of High Temperature Annealing on Defects and Impurities in as-grown semi-insulating 4H SiC”, Journal of Electronic Materials 32, 444 (2003).