Magnetic-field enhancement of the current instability in field-effect transistors

Abstract

A theoretical investigation, within the framework of hydrodynamics, is made of the plasma-wave instability mechanism in a two-dimensional electron fluid in a field-effect transistor in the presence of a perpendicular magnetic field B. Scattering by impurities and/or phonons, termed external friction, is accounted for by adding a damping term to the equation of motion. The treatment is valid for a nondegenerate electron fluid in which the mean free path for interelectronic collisions is much smaller than the device length and the mean free path due to impurities and/or phonons. We show that a relatively low DC current should be unstable because of magnetoplasma-wave amplification due to reflection from the device boundaries. As in the absence of the field B, the instability occurs for 0< v 0< s and v 0<− s, where v 0 is the local electron velocity and s the plasma wave velocity. The field B enhances this instability considerably, as the imaginary part of the wave increases with B, and can outbalance the stabilizing role of the external friction.