Electron localisation in nonstoichiometric films of aluminium nitride produced by reactive sputtering

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Abstract
Thin films of nonstoichiometric aluminium nitride of various compositions (AINx, with 04 Omega -1 cm-1 are found to be well described by the semi-classical Boltzmann equations. In films with room temperature conductivity between 104 Omega -1 cm-1 and 100 Omega -1 cm-1 the conductivity is found to be dominated by electron localisation effects while the thermoelectric power remains free-electron like. This is seen as indicating that the density of states remains unaffected as localisation effects set in. The temperature dependence of films with room temperature conductivity between 0.5 Omega -1 cm-1 and 10-3 Omega -1 cm-1 is found to be well described by the equation sigma (T)= sigma 0T-pexp(T0/T)-s, with s=1/4, thus suggesting that the conduction proceeds by variable-range hopping. Limits on the value of p are established and are used to show that only one theory of variable-range-hopping is consistent with such a temperature dependence.