Growth and physical properties of epitaxial CeN layers on MgO(001)

Abstract

While NaCl-structure transition-metal nitrides have been widely studied over the past two decades, little is known about the corresponding NaCl-structure rare-earth nitrides. Polycrystalline CeN, for example, has been reported by different groups to be both a wide band-gap semiconductor and a metal. To address this controversy, we have grown epitaxial CeN layers on MgO(001) and measured their physical properties. The films were grown at 700 °C by ultrahigh vacuum reactive magnetron sputter deposition in mixed Ar/N2 discharges maintained at 4 mTorr (0.53 Pa). X-ray diffraction and transmission electron microscopy results establish the film/substrate epitaxial relationship as cube-on-cube, (001)CeN‖(001)MgO with [100]CeN‖[100]MgO, while Rutherford backscattering spectroscopy shows that the layers are stoichiometric with N/Ce=0.99±0.02. CeN is metallic with a positive temperature coefficient of resistivity and a temperature-independent carrier concentration, as determined by Hall effect measurements, of 2.8±0.2×1022 cm−3 with a room temperature mobility of 0.31 cm2 V−1 s−1. At temperatures between 2 and 50 K, the resistivity is limited by defect scattering and remains constant at 29 μΩ cm, while at higher temperatures it increases linearly, limited primarily by phonon scattering, to reach a room-temperature value of 68.5 μΩ cm. The hardness and elastic modulus of CeN(001) were determined from nanoindentation measurements to be 15.0±0.9 and 330±16 GPa.