STUDY OF MICROWAVE GENERATION UTILIZING DOUBLE-STREAM INSTABILITIES IN ANISOTROPIC MEDIA.

Abstract : The possibility of two-stream instability in multivalley semiconductors such as silicon and germanium is of interest since the interaction is between light and heavy electrons rather than between electrons and holes. Dispersion relationships for longitudinal two-stream instability in the multivalley semiconductors, silicon and germanium, have been derived. It has been shown for silicon, in which the principal minima are located along the cube axes, that the optimum condition for the instability occurs for the plasma wave propagating in the direction of the cube axes. For germanium, in which the principal minima are located at the zone edges along the body diagonals, the optimum condition for the onset of two-stream instability exists for the wave propagating along the body diagonals. Experimentally, infrared radiation has been observed from pyrolytic graphite (PG) at liquid-helium temperature (4.2 K) using 1-micro sec, 200 A pulses which produce an E-field of 45 v/cm in the sample. Estimates of sample heating (less than 160 K) and the black body temperature required for this amount of radiated power (410 K) indicate that the observed radiation is not due to thermal radiation alone. It is then feasible that the observed radiation is partially due to two-stream instability. Further calibration, spectrum analysis and experimental correlation to theory are required to establish more firmly the source of the observed infrared radiation. (Author)