Transient currents and electron mobility in polythene

Transient currents in polythene were measured by a charge storage method. The relationship between the logarithms of quantity of charge stored and pulse time is linear, if the pulse duration is shorter than a certain critical time; if it is longer, a linear relationship also exists, but the graph has a steeper slope. It is suggested that this critical time is the transit time across the specimen of electrons injected from the virtual cathode. The electron mobility calculated from the critical time is 2·6 × 10 −4 cm 2 V −1 S −1 at room temperature (24 °C) and is associated with an activation energy of about 0·24 eV. The corresponding figures given by similar experiments on polyethylene-terephthalate are 1·0 × 10 −4 cm 2 V −1 S −1 and 0·23 eV. The results are related to a theoretical model for conduction in noncrystalline materials proposed by Mott, and shown to be consistent with it. The model postulates valence and conduction bands exhibiting a tail with strongly localized states which can give rise to electron hopping.