Controlled oxygen vacancy induced p-type conductivity in HfO{2-x} thin   films
  We have synthesized highly oxygen deficient HfO$_{2-x}$ thin films by controlled oxygen engineering using reactive molecular beam epitaxy. Above a threshold value of oxygen vacancies, p-type conductivity sets in with up to 6 times 10^{21} charge carriers per cm3. At the same time, the band-gap is reduced continuously by more than 1 eV. We suggest an oxygen vacancy induced p-type defect band as origin of the observed behavior. 
Erwin Hildebrandt, Jose Kurian, Mathis M. M\"uller, Thomas Schroeder,   Hans-Joachim Kleebe, and Lambert Alff
cond-mat.mtrl-sci