LOW-VOLTAGE CURRENT INSTABILITIES IN LONG ALGAAS GAAS SAMPLES SUBJECTED TO PULSED AND MICROWAVE FIELDS/

High-frequency (10-100-MHz) oscillations and current-switching process es have been studied in long samples of selectively doped Al0.25Ga0.75 As/GaAs heterostructures. The samples ranged up to 5 mm in length. Pul sed and microwave current-voltage characteristics over the temperature range 77-300 K are compared. The onset of the oscillations, observed in a narrow temperature interval near T similar or equal to 200 K, is preceded by a fast (similar or equal to 10-ns) and reversible switchin g of the system into an inhomogeneous, higher-resistance state. A sign ificant decrease in the current after the application of a microwave r adiation pulse is observed at even low values of the microwave field, similar to 10(2)-10(3) V/cm, depending on the temperature. The slow co mponent of the current restoration after the application of a sufficie ntly intense pulse of microwave radiation is of an activation nature w ith an energy similar to 30 meV.