Abstract:
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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