The role of the Ridley-Watkins-Hilsum effect in stabilization of millimeter and sub-millimeter surface electromagnetic waves excited by an electron beam moving parallel to the surface of GaAs

The plasma-beam instabilities have attracted the close attention since 1949 when these instabilities were discovered by Akhiezer, Fainberg and Bohm, Gross. This is due to the possibilities of practical applications of these effects. For instance, the plasma-beam instabilities can be used for the turbulence heating of nuclear plasma, particle acceleration, amplification of high frequency oscillations etc. Nowadays great attention is paid to interactions of electron beams with solid-state plasmas. The solid-state plasma in comparison with the gas-discharge plasma exhibits a whole number of new effects conditioned by peculiarities of energy spectrum of charges, scattering mechanisms and so forth. In the present paper the stabilization of the surface electromagnetic wave excited by an electron beam moving parallel to a semiconductor (GaAs) boundary is considered within the framework of hydrodynamic approach. The stabilization occurs due to peculiarities of band structures of A^IIIB^V semiconductors (and GaAs in particular). The electrons of the semiconductor in the unexcited condition are known to be in the center of the Brillouin zone (in the direction of <000>). When the magnitude of the external electric field is greater than the energy gap between the center of the Brillouin zone and the valleys in the directions <100> the transitions of electrons between these valleys occurs (the Ridley-Watkins-Hilsum effect). The momentum frequency of these transitions increases with increasing magnitude of the external electric -field. The last one is the cause of stabilization of instabilities of the surface electromagnetic wave and the oscillations of the surface electron densities of both an electron beam and the semiconductor