Drift mobility techniques for the study of electrical transport properties in insulating solids

Abstract The paper reviews in some detail the principles and experimental techniques involved in drift mobility measurements. These are particularly suitable for transport studies in highly resistive, low mobility solids and examples of their application to crystalline and non-crystalline materials are given. A platelet specimen is fitted with electrodes on opposite sides and charge carriers are generated near the top electrode by a fast excitation pulse. Both light and electron pulses have been used and the particular advantages of electron beam excitation are discussed. A steady or pulsed applied field draws one type of carrier across the specimen and the transit time tt is determined either by charge integration or from the observed current transient. This leads directly to the drift mobility. A section of the paper deals with the effects of trapping on the measurements. Shallow centers, possessing a release time constant τ r « t t , lead at lower temperatures to a transport controlled by multiple trapping and release. Measurements in this range give information about such centres. Deep traps introduce disturbing polarisation effects and ultimately limit the applicability of the method. Details of a space charge neutralisation technique are given. A different, more “static” method developed by Davis is briefly described.

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