High-energy vibrational modes in nitrogen-doped ZnO

We present results of Raman-scattering experiments on a series of nitrogen-doped ZnO epilayers grown by chemical vapor deposition. Nitrogen, a potential acceptor in ZnO, was introduced by the thermal decomposition of ammonia (NH3). We found a structure consisting of at least four lines with frequencies of 2253, 2277, and 2304 cm(-1). They increase in intensity simultaneously with additional modes in the energy range of the host phonons: both scale with the nitrogen concentration in the samples. The origin of the high-energy structure is tentatively assigned to vibrations of lattice-bound nitrogen or complexes, composed of the constituents of the dopant NH3.