Static Space Charge and Capacitance for Two-Blocking Electrodes

A one-dimensional treatment is presented of space-charge effects in materials having two charge-blocking electrodes. Especial attention is given to the situation where univalent, mobile charge carriers of only one sign can recombine bimolecularly with fixed charges of opposite sign; however, the case where noncombining charges of both signs are mobile is also included. Space-charge potential distributions and differential capacitance cannot be obtained explicitly in the general case but have been accurately calculated using a digital computer. Potential vs distance and capacitance curves are presented which illustrate dependence on applied potential, separation of electrodes, and recombination ratio. The results show features often observed experimentally for a wide variety of materials such as photoconductors, semiconductors, and insulators. The treatment is applicable for much higher applied potentials than is the case for the previously considered one blocking electrode situation with charge accumulation at the blocking electrode.