  We present a heterojunction theory of ultrathin organic multi-layered
devices, which is the revision of our previous work. Their characteristic
feature is the generation of conductive space charge region in the insulating
neutral dielectric region under the bias voltage application, while the
insulating space charge region is generated in the conductive neutral region in
the case of semiconductors. We propose the concept of quasiconductor to
describe these features. From the theory, the capacitor equation of mobile
carriers is given, which is an equivalent equation of the Mott-Schottky
equation in semiconductor physics. Because the organics are dielectrics, the
dynamics are controlled cleverly by polarization. The theory gives a relation
among the applied voltage, carrier accumulation, mobility, and carrier density,
which enables the in-situ simultaneous evaluation of mobility and the carrier
density of ultrathin organic multi-layered devices. The concept of
quiasiconductor is a missing link between organic electronics and the
semiconductor physics.
