Low frequency oscillations in semi-insulating gallium arsenide†

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Abstract
Low frequency oscillations associated with trap-controlled moving domains in high resistance semiconductors have been studied by a number of investigators. The mechanism involved is (in increase of the capture cross section of a repulsive centre with increase in the applied electric field. Although many of the features involved have been established by experimental studies, the modelling and analysis available have so far been incomplete. The present paper shows that computer studies can make a contribution to understanding of the domain behaviour and the effects of illumination. Using a simple functional form for the capture coefficient of a repulsive centre in GaAs, the non-linear equation obtained can be shown to result in a dipole domain propagating with constant velocity for bulk material. The threshold for domain nucleation was 860 volts/cm. Domain velocities were found to increase with illumination level and applied voltage, and for the model considered ranged from 0-25 cm/sec in the dark to 125 cm/sec under illumination. The domain width increased with applied bias and varied from 0.05 to 0.15 cm. The domain consisted almost totally of fixed space charge, and was closely symmetrical in shape.