Image patterns of current density filaments formed during low-temperature impurity breakdown in high-purity n-GaAs have been investigated at 4.2 K by means of the spatiotemporal photoluminescence (PL) patterns. Under a pulsed voltage with the pulse width of w = 18.0 mus and the repetition frequency of 8.0 kHz, a current density filament can be observed as a quenched PL pattern, Besides, anomalously bright PL pattern was observed along the filament boundaries. With a short pulse of w = 785 ns, the bright PL pattern was formed inside the current filament. The anomalous enhancement of the PL intensity was attributed to the electron-impact formation and/or the hole-impact formation of the excitons bound to ionized donors during the impact ionization avalanche of the neutral shallow donors. (C) 2002 Elsevier Science Ltd. All rights reserved. References: 22
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