Oscillatory bistability of real-space transfer in semiconductor heterostructures

Charge transport parallel to the layers of a modulation-doped GaAs/Alₓ{Ga}_{1{{-}}x}$As heterostructure is studied theoretically. The heating of electrons by the applied electric field leads to real-space transfer of electrons from the GaAs into the adjacent ${Al}ₓGa_1-xAs layer. For sufficiently large dc bias, spontaneous periodic 100-GHz current oscillations, and bistability and hysteretic switching transitions between oscillatory and stationary states are predicted. We present a detailed investigation of complex bifurcation scenarios as a function of the bias voltage U₀ and the load resistance RL. For large RL subcritical Hopf bifurcations and global bifurcations of limit cycles are displayed.