Nucleation process of a filamentary current during impact ionization avalanche in n-GaAs

The nucleation process of a current filament has been investigated in n-GaAs during the impact ionization avalanche of neutral shallow donors at 4.2 K. The image patterns of the current filament are measured under a pulsed electric field with the pulse width T-p by detecting quenched patterns of photoluminescence from the laser-excited sample. It is found that the rudimentary filament is formed with the pulse width T-p 900 ns and the pulse height V-p 0.79 V. Fronts of the nucleated filament at the cathode (or the anode) propagate towards the anode (or the cathode). Drift velocity and drift mobility of the fronts are estimated as a function of the pulse width. We also investigate the nucleation process under the transverse magnetic field.