Relaxation space charge limited

Unambiguous steady-state measurements are carried out only in the trap-free space-charge-limited-current (SCLC) regime (23), when the average transit time (f j of any excess injected carrier across the sample bulk is shorter than the time required for the bulk to locally neutralize the carrier (22). The transit time ( r) has been defined in equation 1. The time to neutralize any excess injected carrier is the bulk dielectric relaxation time, Tr ( r = in which p is the bulk resistivity and e is the bulk dielectric... 

Contacts must supply a reservoir of carriers ready to enter the semiconductor at the rate required by the ohmic currents. At low fields, the balance is maintained by dielectric relaxation which quickly compensates any deviation from equilibrium by a charge supply from the interior and from the other contact. At high fields departures from this balance occur. When the contact region has an abundance of carriers the ohmic extrapolation is exceeded by space charge supplied currents. These are called by the misnomer space charge limited currents . When, on the other hand, the demand for carriers exceeds the supply, the current becomes emission limited. A very comprehensive account of injection in insulators has been given recently by Lampert and Mark (1970), Lampert and Schilling (1970), and by Baron and Meyer (1970). The injection processes in insulators and amorphous semiconductors differ markedy from minority carrier injection in crystalline semiconductors where the majority carrier density adjusts... 

On the other hand, since for the sine-form field dE/dt oc caE the role of permanent conductivity ct decreases with increasing frequency, in the high frequency limit (0 >> 1/tm = 47ta/ a material can be considered as non-conductive. The time Tm = /4tict is called Maxwell dielectric relaxation time. Later we shall meet it again under another name space charge relaxation time . 

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