On the Observation of Transient Space-Charge-Limited Currents in Insulators

The conditions for the observation of space-charge-limited (SCL) transient current pulses in insulators are examined. A parameter α=2tr/τ (tr=space-charge-free transit time and τ=response time of the circuit) is defined, whose value determines the extent to which the pulses are distorted from their ideal shape. For α>100, the pulses are undistorted. For 20<α<100, the pulse shape becomes distorted from the ideal case and for α<20, pulses begin to be indistinguishable. It is shown that carrier transport in any insulator may be investigated by transient SCL current measurements provided that trapping is not too severe and that ohmic contact formation (either transient or steady-state) is possible.