MEYER-NELDEL RULE IN UNDOPED a-Si:H, EXAMINED BY TM-SCLC METHOD.

The preexponential factor sigma //o of the electrical conductivity as a function of its activation energy E//a (so called Meyer-Neldel rule) has been studied at room temperature on undoped a-Si:H by means of the temperature modulated space-charge-limited-current (TM-SCLC) method in an annealed state A and after prolonged illumination (state B). With the increasing illumination time two different processes are observed. In an annealed and lightly illuminated state, sigma //o versus E//a dependence cannot be decribed by a single Meyer-Neldel coefficient G, but exhibits the change of the slope at about E//a approximately equals 0. 6 eV, from G approximately equals 10 eV** minus **1.