Spectroscopic study of Nd-doped amorphous SiN films

Neodymium-doped amorphous silicon-nitrogen (a-SiN) thin films have been prepared by cosputtering a (Si+Nd) target in a nitrogen atmosphere. After deposition the films were submitted to cumulative thermal annealing treatments and investigated in detail by Raman scattering spectroscopy, optical transmission, x-ray photoelectron spectroscopy (XPS), and photoluminescence techniques. Additional information was also obtained from ion beam analyses such as Rutherford backscattering spectrometry and nuclear reaction analysis. As a result of the deposition method and conditions, the films are amorphous and contain ≅0.8 at % of neodymium. Actually, Raman scattering measurements indicate that the present films remain amorphous even after thermal anneal at 1000 deg. C. The electronic states at the top of the valence band of the Nd-doped a-SiN films were investigated by XPS, which indicates that most of the neodymium present in the a-SiN host stays under the trivalent (Nd3+) form. As a consequence, relatively strong and well-defined photoluminescence signal could be observed in the infrared energy range corresponding to internal 4f transitions due to the Nd3+ ions. The achievement of this optical emission is highly susceptible both to the thermal annealing treatment and to the energy of photon excitation. Whereas the former determines the atomic environment of the Nd3+ ions, the latter indicates the most efficient route to their optical excitation. Based on various experimental techniques, and as a result of a systematic investigation, the present manuscript contains an extended and comprehensive discussion on the principal spectroscopic characteristics of the Nd-doped amorphous SiN system