Bistability and negative photoconductivity in optically induced real-space transfer

Optically induced charge transport in a modulation-doped GaAs/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As heterostructure is studied theoretically. Intersubband excitation of electrons in the GaAs quantum well due to infrared absorption leads to their real-space transfer into the adjacent ${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As layer. We derive a system of nonlinear model equations considering as relevant physical mechanisms the generation-recombination processes in GaAs, longitudinal and transverse dielectric carrier relaxation, as well as resonant and nonresonant tunneling across the interface, and analyze its behavior with the methods of nonlinear dynamics. We predict optoelectronic bistability associated with different photoconductive responses between the two locally stable steady states corresponding to different types of tunneling prevalent: the regime of dominant resonant-tunneling currents shows negative differential photoconductivity, whereas the nonresonant tunneling state is practically invariant with respect to changes of the IR intensity.