ELECTROSTATIC EFFECTS OF INTERFACE STATES ON CARRIER TRANSPORT IN SEMICONDUCTOR HETEROJUNCTIONS

A theory of the electronic transport properties of contacts between two dissimilar semiconductors is presented, which includes the effects of bias-dependent interface state charge on the electrostatic potential distribution in the contact. The quasi-Fermi level for the interface states is determined by the competition between the capture of electrons and holes at the interface for a given bias voltage. The conditions for diffusion-limited or thermionic-emission-limited current flow are defined in terms of heterojunction parameters and material properties. Ignoring the direct recombination currents through interface states, the interface states have no effect on diffusion-limited current, but when the transport is limited by the thermionic emission of carriers there are pronounced electrostatic effects on this current from interface states. A limiting density of interface states ∼10 11-1012 cm-2 eV-1 has been established above which the current-voltage (J-V) relations are independent of the parameters characterizing these states, and for this condition the n* value of the exponential J-V characteristics is ≃2 over an appreciable range of bias voltage.