Three‐level oscillator in indium phosphide

A microwave oscillator with three electronic levels instead of two has been built by Cyril Hilsum and his collaborators at the Royal Radar Establishment in Malvern, UK. At the International Conference on the Physics of Semiconductors (at MIT in August) Hilsum said he had made a three‐level microwave oscillator that oscillated sinusoidally at frequencies higher than the Gunn effect would produce. He made the oscillator out of indium phosphide after predicting theoretically that the device should work. One solid stater remarking on the work said, “It shows we really understand the solid state well enough that we can almost design materials.”