Stability and structure of hydrogen defects in zinc oxide
Slade J. Jokela, Ph.D.
Washington State University
Chair: Matthew D. McCluskey
Zinc oxide (ZnO) is a wide band gap semiconductor with potential optical, electronic,
and mechanical applications. First-principles investigations predicted that hydrogen
impurities act as shallow donors in ZnO. IR spectroscopy showed that hydrogen
exhibits a local vibrational mode at 3326.3 cm?1, at liquid-helium temperatures,
corresponding to an O-H type bond. Results from high-pressure and polarized IR
spectroscopy strongly suggest that hydrogen occupies an antibonding location with
an O-H bond oriented at an angle of 110.6o from the c axis. By correlating the IR
absorbance strength with free-electron concentration, it was established that the O-H
complexes are shallow donors. However, the O-H donors are unstable, decaying significantly
after several weeks at room temperature. The kinetics of the dissociation
follow a bimolecular decay model, consistent with the formation of H2 molecules. Attempts
at chemical vapor transport (CVT) growth of ZnO crystals were successful.
Results varied from Zn-rich, orange-colored samples to nearly colorless ZnO polycrystals.
Further analysis revealed an unknown contaminant that became apparent after
annealing in hydrogen, resulting in an IR absorption peak at 3150 cm?1.
School:Washington State University
School Location:USA - Washington
Source Type:Master's Thesis
Keywords:zinc oxide hydrogen bonding wide gap semiconductors
Date of Publication: