Coherent Microwave Instabilities in a Thin-Layer Solid-State Plasma

Abstract

Coherent microwave radiation at frequencies from 6.5 to 44 GHz is generated by p-type indium antimonide at 77°K with an injected electron current transverse to a magnetic field. With a waveguide or stripline coupling system, the maximum output power is about 10 μW for input power levels of 1 to 5 W. Grooves of specified widths cut into the Suhl surface of the rod-shaped InSb samples generate the coherence and determine the approximate output frequency. Wavelength measurements of a surface wave on the rod show that the effective groove width is about equal to a half-wavelength. A theory of double-stream interaction in a thin plasma layer with a magnetic field transverse to the current flow is formulated and predicts instabilities in the observed frequency range. Correct quantitative predictions made by the theory are: (1) the hole density required for onset of emission, (2) the minimum magnetic field which is required for emission onset at high current injection, (3) the phase velocity of the surface wave, and (4) the magnetic field value at which the high field mode executes a frequency minimum. Computer solutions of the dispersion relationship for the plasma wave instability are in good qualitative agreement with measurements of the emission frequency as a function of magnetic field and injection current. The theoretical analysis and concurrent experimental evidence demonstrate the existence of an instability in a thin-layer plasma in the absence of a magnetic field.