Field distribution in junction field-effect transistors at large drain voltages

An analytical approximation to the field distribution in the channel portion between gate and drain of the junction field-effect transistor is derived, assuming an infinitely small channel width-to-height ratio, and modified for finite channel widths by introducing an effective impurity concentration which depends on drain current. The approximation is applicable also in the limiting case of zero gate edge curvature, i.e., for Schottky-barrier gate. The theoretical field distribution is used to extract impact-ionization coefficients from published experimental data on gate current enhancement at large drain voltages. These impact-ionization coefficients agree with published data derived from bulk impact ionization.