Two-Stream Instability in Semiconductor Plasmas

Pines and Schrieffer demonstrated that the two-stream instability could occur in a high-mobility semiconductor such as InSb if the conditions ωp+τ+>10 and T−»T+ are satisfied, where ωp+ is the hole-plasma frequency, τ+ is the hole-collision time and T− and T+ are the electron and hole temperatures, respectively. Either condition is difficult to obtain in bulk InSb. The possibility of observing such an instability in a structure consisting of adjacent p and n InSb is considered. The collision condition is reconsidered using a collision term which conserves particles and assuming the somewhat higher electron-drift velocities (≃electron-thermal velocity) which are now believed possible. It is concluded that the condition can be relaxed by about an order of magnitude (ωp+τ+>1). The layered structure could provide the condition T+«T− if it were in contact with liquid helium while a current, passed only in the n region, produced both relative streaming and elevated electron temperatures. A comparative stability analysis in the zero-temperature fluid limit indicates that the surface space-charge waves of the layered structure can grow at rates only slightly less than those of the bulk space-charge waves of the corresponding penetrating stream system.