Current Oscillations and High-Field Domains in Photoexcited High-Resistivity GaAs

Abstract

Current oscillations (10 kHz∼10² kHz) due to the periodic generation of a moving high-field domain have been observed in high-resistivity GaAs (∼3×10³ ohm-cm in the dark) under illumination at room temperature. It has been found that threshold field for the oscillation decreases with increasing illumination level and lies in the range from 650 V/cm to 2100 V/cm. Properties of the high-field domain have been investigated by a light probe and a contact probe technique. The domain velocity is 10³ cm/sec∼10⁴ cm/sec. Width and field of the domain are of the order of 10^-2 cm and 10⁴ V/cm, respectively. By shifting a light spot position along the specimen to change the distance that the domain transits, the oscillation frequency can be varied continuously. The origin of the oscillations can be explained with field-enhanced electron trapping at deep levels.