Recent work on the direct generation of microwaves in bulk semiconductors

When a pulsed electric field of several kV cm^-1is applied to a homogeneous specimen of III-V semiconductor by means of "ohmic" contacts, an instability in the current is observed. Under suitable circumstances this instability takes the form of an oscillatory component superimposed upon the normal pulse current. The period of oscillation is then equal to the transit time of electrons between the contacts. Frequencies between 0.5 and 6.5 Gc/s, peak powers up to 0.5W, and efficiencies of 1-2% have previously been reported for n-type Ga-As. In this paper, the observation of the same phenomenon in other materials, including n-type InP, will be reported, and the design and performance of a solid-state microwave oscillator based on the effect will be discussed. This oscillator permits the generation of useful amounts of microwave power by a simple device which operates at room temperature without a magnetic field, which contains no p-n junctions, has no inconveniently small dimensions, and which should be cheap to manufacture.