Instabilities of Semiconductor Plasmas in Crossed Electric and Magnetic Fields

Abstract

It is shown that in a slab of a semiconductor plasma subject to crossed electric and magnetic fields, a gradient in carrier density perpendicular to the magnetic field can cause a plasma density wave instability. General forms of the carrier density distribution and the dispersion relation are derived. Two types of instabilities, each of which has its equivalent in helical instability, are discussed, i.e., one caused by a density gradient which is established by the Lorentz force, and the other by a gradient due to the unsymmetry of the surface recombination velocities. Critical electric and magnetic fields for the onset of instability agree qualitatively with those observed in current oscillations in germanium under the same field configuration, especially for low magnetic fields. Possibility of applying the theory to the explanation of the oscillations in indium antimonide is indicated.