Turing bifurcation during the nucleation process of a current density filament in n-GaAs

The nucleation process in spatiotemporal structures of a current density filament in n-GaAs has been investigated under a de + ac driving force V-dc + V-ac sin 2 pi f(d)(t) at 4.2 K. With V-dc, = 0.8 V, V-ac = 665 mV and f(d) = 100 kHz, we observe an S-shaped I-V curve caused by impact ionization avalanche of neutral shallow donors and subsequent formation of a well-defined current density filament. In the nucleation process, Turing bifurcation is observed at around the breakdown voltage, followed by a spatially periodic pattern of the current density as a pre-filament state. (C) 2000 Elsevier Science Ltd. All rights reserved.