Small-signal analysis of semiconductor heterojunctions with interacting interface states

A small-signal analysis of electrical conduction is given for semiconductor heterojunctions with a continuous density of states distribution inside the gap. The defect states are supposed to fully interact, such that their occupation can be described by a Fermi function with a quasi-fermi energy for non-equilibrium situations. After numerical integration of Poisson's equation and the continuity equations for electrons, holes and defect states one obtains the capacitance-frequency and conductance-frequency characteristics, depending on defect concentration, density of states function, temperature and applied voltage. Application to a InGaAs/lnP heterojunction shows characteristic features due to the presence of interface states. The analysis illustrates the differences with the case of discrete interface states, continuous distributions of non-interacting states, and of bulk defects.