Charge Carrier Transport in a Molecularly Doped Polymer: Dispersive versus Gaussian

A typical molecularly doped polymer (bisphenol-A-polycarbonate containing 30 mass% of hydrazone DEH) has been put to thorough experimental examination by both time of flight and radiationinduced conductivity methods. A much improved measurement technique incorporating a computerassisted registration scheme that allows one to record a complete current transient over up to five decades in time in one single shot was employed. Studies of radiation-induced conductivity (conductivity proper as well as transit effects) uniquely prove the dispersive rather than the Gaussian transport of holes (majority carriers) in this polymer. The shape of the time-of flight current transients is strongly influenced by some extraneous factor, presumably surface traps, whose role in radiation-induced conductivity could hardly be detected. We describe the phenomenon quantitatively using a multiple trapping formalism. A critical discussion of the present situation in the field of charge carrier transport in disordered solids is also included.