INTERFACE STATES AT LATTICE-MATCHED AND PSEUDOMORPHIC HETEROSTRUCTURES

To obtain information concerning interface states at lattice-matched and pseudomorphic heterointerfaces, a rigorous computer simulation of the capacitance-voltage (C-V) curves of the selectively doped AlGaAs/InxGa1-xAs/GaAs heterostructures was carried out and fitted to experimental curves. The values of the conduction band discontinuity determined by fitting agree well with the previous results. Presence of a significantly high density of interface states of a particular nature is demonstrated for the first time. They possess a U-shaped energy distribution and consist of donor and acceptor states with a characteristic charge neutrality level. The result can be explained by the disorder-induced gap-state (DIGS) model. Previously reported negative interface fixed charge is due to filled acceptor states. The state density increases with the increase of the lattice mismatch, showing steep exponential rise above the critical layer thickness. An anomalous behavior was observed in a completely relaxed sample, indicating Fermi level pinning due to misfit dislocations.