Low field thermally assisted charge injection at electrode/polyethylene interfaces observed by space charge measurements

A layered sample consisting of a polyethylene (PE) film and a both surface fluorinated PE plate was used to investigate the charge injection at the semicon, Al, or Au electrode/PE interface by space charge observation based on the pressure wave propagation method, to determine whether it is a thermally assisted process. Space charge observation of the layered sample subjected to an averaged dc field of positive or negative 5 kV/mm shows that charge injection at the electrode/PE film interfaces occurs and charge accumulation at the film/surface fluorinated plate interface does not stop so long as the interface electric field is nonzero, independent of the electrode material. The charge injection and accumulation rates strongly depend on the poling temperature, showing a significant thermally assisted effect. A thermally assisted tunneling and/or thermal assistance of electrons from the occupied electrode-induced gap states to the bulk states originating in PE itself can account for the observation of no threshold field for the charge injection.