High-Mobility Electron Conduction in Oxynitride: Anatase TaON

We report on a new route for synthesizing metastable anatase tantalum oxynitride (TaON) in thin film form on lattice-matched (LaAlO3)(0.3)-(SrAl0.5Ta0.5O3)(0.7) (LSAT) single crystals by using nitrogen plasma assisted pulsed laser deposition. Epitaxial stress from the substrate stabilized the anatase structure without the need for doping an impurity, such as Sc or Mg, which is required in conventional bulk synthesis by ammonolysis. X-ray diffraction measurements and cross-sectional transmission electron microscope (TEM) observations demonstrated the growth of phase-pure anatase TaON thin films with the epitaxial relationships (001)(TaON) parallel to (001)(LAST) and [100](TaON) parallel to [100](LSAT). A high growth temperature (>= 750 degrees C) and a balanced supply of oxygen and nitrogen are crucial for obtaining high-quality anatase TaON thin films. The films grown at 800 degrees C exhibited good n-type conduction with a resistivity of similar to 1 X 10(-2) Omega cm. The source of the carrier electrons was likely anion vacancies. The Hall mobility of anatase TaON (similar to 17 cm(2)V(-1)s(-1) at 300 K) is comparably high to that of anatase TiO2, which is a well-known oxide semiconductor with the same crystal structure and d(0) electronic configuration. The bandgap and refractive index of anatase TaON thin films were 2.37 eV and approximately 3.0, respectively, in the visible region.