ELECTRIC-FIELD HEATED ELECTRONS IN A-SI-H - NEW FEATURES

The subnanosecond time-of-flight measurement at very high electric fie ld (less than or equal to 0.55 MV/cm) and at high temperatures (300 K < T < 450 K) allowed one to achieve the full deactivation of the elect ron drift mobility in a-Si:H and thus almost to eliminate the influenc e of shallow trapping. From the temperature dependence of high tempera ture drift mobility at low electric fields the value of band mobility (mu(0) = 6.5 cm(2)/V s) is determined, which appears to be temperature independent. The field dependence of the drift mobility indicates tha t the mu(o) has to decrease with increasing field when the drift veloc ity exceeds the sound velocity. At very high electric fields drift vel ocity saturation has been observed, which we explain by a model based on optical phonon emission, similar to the behaviour of hot carriers i n crystalline semiconductors.