Negative differential conductance and bistability in undoped GaAs/AlGaAs quantum-cascade structures

We discuss the mechanisms for negative differential conductance NDC and bistable behavior observed in the current-density–electric-field j-F characteristics of undoped GaAs/Al0.45Ga0.55As quantum-cascade structures QCSs . While the j-F characteristic of a QCS with a single period exhibits NDC without bistability, NDC and a bistable behavior are observed for a QCS with 20 periods of the same design. Calculations using a scattering-rate model neglecting any field inhomogeneities show that the interplay of resonant tunneling between the states in the QCS with resonant scattering of longitudinal optical phonons can lead to NDC in both structures. However, the bistable behavior in the QCS with 20 periods can only be explained if an inhomogeneous field distribution due to charge accumulation is taken into account in addition to the NDC. The abrupt decrease of the current density at the field strength of the bistability is attributed to a rapid decrease of the accumulated charge, which is confirmed by electric-field-dependent photoluminescence spectroscopy.

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Author Stephen W. Teitsworth Physics