Theory of space-harmonic traveling-wave interactions in semiconductors

Strong coupling can be obtained between slow space-charge waves in thin biased semiconductors and long-wavelength microwave fields, if the semiconductor is overlaid with an insulated periodic mosaic of tiny metal stripes. Microscopic field perturbations are represented by a set of slow space-harmonic waves traveling in opposite directions, with a standing-wave interference pattern which matches the periodicity of the mosaic. When the carrier drift velocity is approximately synchronized with one of the space-harmonic waves, interaction is enhanced, space-charge waves may be induced, negative-resistance effects may appear, and power may be coupled from the semiconductor into external microwave networks. Theory indicates that the principle can be used to obtain microwave amplification or oscillation in thin biased layers of normal semiconductors such as silicon or germanium. It may also be possible to couple efficiently in this way to traveling Gunn-effect domains in extensive thin layers of gallium arsenide.