The effect of illumination on Gunn oscillations in epitaxial GaAs

Coherent Gunn oscillations have been observed in long samples of epitaxial GaAs grown by both the solution and the vapor-transport methods on semi-insulating GaAs substrates. Samples of low carrier concentrations which do not exhibit Gunn oscillations, and samples which oscillate incoherently in the dark, oscillate coherently when illuminated. Illumination is observed to lead to an improvement in the peak current-to-valley current ratio.