Magnetic-field effects on undriven chaos in a weakly coupled GaAs/AlAs superlattice

We have investigated the effect of a perpendicular magnetic field on the spontaneous current oscillations in a weakly coupled GaAs/AlAs superlattice. At zero magnetic field, voltage regions of periodic as well as chaotic oscillations are observed. With increasing magnetic field B, the voltage regions for chaotic oscillations become larger and those for periodic oscillations smaller. At B=9 T, the whole voltage range consists of chaotic oscillations. At the same time, the time-averaged current-voltage characteristic hardly changes. The experimental observations demonstrate that the quantization by the perpendicular magnetic field results in an equalization of the sequential resonant tunneling process over the whole superlattice, suppressing scattering effects due to disorder. (C) 2000 American Institute of Physics. [S0003-6951(00)03120-X].