The Meyer-Neldel rule in the conductivity of insulating germanium nitride and oxynitride films

Electrical conductivity, σ(T ), of a-Ge3Nx (3.7 < x < 4.6) and quasi-stoichiometric a-Ge2OyNx films has been investigated as a function of the temperature. Layers present a highly insulating behavior with conductivity and thermal activation energy rapidly rising, increasing T from room temperature to 600 K. Depending on the film composition, the conductivity can vary up to six orders of magnitude. Data analysis of σ(T) revealed a clear relation between the pre-exponential factor and the thermal activation energy, suggesting the validity of the Meyer- Neldel rule. For all investigated films, typical Meyer-Neldel parameters assume values in a narrow range: 10−8 < σ00 < 10−6 (Ωcm)−1 and 41 < EMN < 51 meV. To account for this behavior we have considered a model based on a sta- tistical shift of the Fermi level upon the temperature raise. Our study is the first experimental evidence of this kind of electrical behavior in this class of materials.