Bipolar Charge-carrier Injection In Semiconductor/insulator/conductor Heterostructures: Self-consistent Consideration

摘要

A self-consistent model of bipolar charge-carrier injection and transport processes in a semiconductor/insulator/conductor system is developed, which incorporates space-charge effects in the description of the injection process. The amount of charge carriers injected is strongly determined by the energy barrier emerging at the contact, but at the same time the electrostatic potential generated by the injected charge carriers modifies the height of this injection barrier itself. In our model, self-consistency is obtained by assuming continuity of the electric displacement and of the electrochemical potential all over the system. The constituents of the system are properly taken into account by means of their respective density of state distributions. The consequences resulting from our model are discussed on the basis of an indium tin oxide/organic semiconductor/ conductor structure. The distributions of the charge carriers and the electric field through the electrodes and the organic layer are calculated. The recombination- and current-voltage characteristics are analyzed for different heights of injection barriers and varying values of the recombination rate and compared with the measured current-voltage dependences for an indium tin oxide/poly(phenylene vinylene)/Ca structure. The voltage dependences of the recombination efficiency for the different values of injection barriers and recombination rate reveal optimum conditions for the device performance.