The Nature of Helicon-Wave Instabilities

The generalized dispersion relation for electromagnetic waves in a medium with drifting carriers is calculated in the hydrodynamic description of plasmas. The basic configurations of k, B0 and E0, involving the velocity-driven instabilities in semiconductor plasmas are discussed briefly. As a special case, helicon-wave instabilities when k// B0// E0 are studied in detail by a “resistive hole approximation.” It is shown that the left-polarized-helicon instability is convective (amplifying) for (n 0h /n 0e )(ω c e τ e )(ω c h τ h )<1, and non-convective (absolute) for (n 0h /n 0e )(ω c e τ e )(ω c h τ h )≧1.