On the origin of an additional Raman mode at 275 cm-1 in N-doped ZnO thin films

A systematic investigation on the optical properties of N-doped ZnO thin films was performed in order to understand the origin of an additional Raman mode at 275 cm(-1). This Raman peak was observable only at N-2 pressures lower than 30 Pa during pulsed laser deposition. Its intensity decreased with an increase of N-2 pressures and eventually vanished at pressures above 30 Pa. N substitution of O (N-O) was identified by photoluminescence and x-ray photoelectron spectroscopy and correlated well with the Raman intensity. The electrical measurements showed significant changes in resistivity, charge carrier concentration, and mobility due to the presence of N acceptors. Investigations on undoped ZnO films grown in Ar without N-2 further confirm that N doping plays a key role in the Raman scattering. The experimental data indicate that the Raman mode originates from N-O related complexes, likely in the form of Zn-i-N-O. These investigations help to understand the doping mechanisms and underlying physics of the additional Raman mode in the ZnO films. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3697971]