Microwave oscillations in high-resistivity GaAs

It has been found that Gunn-effect oscillations in high-resistivity GaAs cease when the product of the conduction electron density and the sample length drops below 10¹¹cm^-2as predicted by theory. The samples investigated exhibited impact ionization of a deep donor level lying 0.41 eV below the conduction band edge when subjected to an applied electric field equal to the Gunn-effect threshold field. Some observations concerning space-charge limited injection of electrons and concerning electrical breakdown in high-resistivity GaAs are also reported.