Drain conductance of junction gate FET's in the hot electron range

Abstract

A new model is proposed for the drain conductance of J-FET's in the hot electron range. The model is based on a physical picture revealed through two-dimensional numerical analysis. The two-dimensional analysis shows that the electron concentration changes gradually at the boundary of a depleted region which is defined by a conventional theory. Because of this gradual change, electrons can remain after the pinch-off and contribute to the drain current. Although the high electric field causes the electron velocity to saturate, the drift velocity vector rotates into the x axis (source-to-drain) with the increase in the drain voltage. The increase in the x component V x of the drift velocity gives rise to a small increase in drain current, that is, a finite drain conductance. The proposed model takes into account the above two essential features, gradual change in electron distribution, and the rotation of the velocity vector. This model is constructed in a single formulation which describes the current-voltage characteristics from the linear to the saturated drain-current region. Theoretical calculations agree quite well with the experiment on GaAs Schottky barrier gate FET's.