Conditions for current or field stratification in an electron-hole plasma

An analysis is made of the stability of a homogeneous state of an electron-hole plasma heated by an electric field. Particular attention is given to plasmas in which the electron density n is not less than the hole density p and the effective masses of the carriers are quite different (m/sub n/(>>m/sub e/). It is shown that stability is lost when the differential conductivity is positive and there are fluctuations with a particular wave vector k directed at an angle phi = 0 to the lines of flow of current (field stratification) or at phi = π/2 (current density stratification). The stratification of the current occurs when the ratio p/n is sufficiently small. As the nonequilibrium hole density increases, for example by photogeneration, there is a transition from the current to the field stratification at a particular ratio of carrier densities, and at a critical heating. It is shown that the current stratification is due to the presence of a local ''latent'' S-type current-voltage characteristic of the plasma, and field stratification is due to a local ''latent'' N-type characteristic. The external conditions and plasma parameters under which stratification occurs are determined on the basis of these local ''latent'' many-valued characteristics. The results for the various possible cases are tabulated