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

Abstract : Momentum relaxation times for hot electrons in individual valleys in germanium were calculated by extending the theory of Reik and Risken. The net growth rate was calculated for two-stream instability at 77 K for an applied electric field of 1000 V/cm. The damping of the plasma wave due to collisions of hot carriers in the valleys -2- through -4-, which provide shielding for the slow electrons in the first valley, is appreciable but damping due to collision of slow electrons is even more serious. Reducing the lattice temperature to 4 K will not improve the situation much, and increasing the doping to raise the plasma frequency does not appear to sufficiently overcome the collisional damping, at least within the doping range for which the present theory is valid (less than 10 to the 18th power/cc). The InSb photoconductive submillimeter wave detector was improved by the use of high purity InSb. Improved bismuth sample holders eliminated the cleavage of trigonal direction bismuth samples due to thermal stresses. However, the drift velocities obtainable are still only marginally sufficient to produce two-stream instabilities before heating and melting of the sample occurs. Experiments to observe the instabilities with an InSb detection system having a sensitivity of approximately minus 40 dbm were unsuccessful. (Author)