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 donor s at 4.2 K. The image patterns of the current filament are measured un der a pulsed electric field with the pulse width T-p by detecting quen ched patterns of photoluminescence from the laser-excited sample. It i s 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 fil ament at the cathode (or the anode) propagate towards the anode (or th e cathode). Drift velocity and drift mobility of the fronts are estima ted as a function of the pulse width. We also investigate the nucleati on process under the transverse magnetic field.