Abstract
High‐frequency (MHz) and low‐frequency (kHz) current oscillations are found in photoexcited long GaAs diodes; the threshold field for the former is about 4.0 × 103 V/cm, and for the latter is about 1.5 × 103 V/cm. At an average applied field >4 × 103 V/cm, high‐frequency oscillation occurs first and continues for a while, then low‐frequency oscillation takes place. Experimental results suggest that the origin of high‐ and low‐frequency oscillation are different from each other; the former is the two‐valley transfer effect, and the latter the field‐dependent trapping effect.