Effect of mesh spacing on static negative resistance in GaAs MESFET simulation

Norton [1], [2] has postulated that the negative differential resistance in the drain characteristics of GaAs MESFET´s which is predicted by device simulations may arise solely because the computational mesh spacing is too large, and he has presented finite difference calculations showing the effect in InP. This letter describes a 0.25-µm-gate length GaAs MESFET which is simulated in two dimensions using the finite-element method. The drain current calculated reveals a static negative differential resistance region for low drain-source and gate-source bias voltages. The value of the drain current and the differential negative resistance calculated are insensitive to the mesh spacing until extremely coarse mesh spacings are used. The grid constraint of Norton is, therefore, seen to be too stringent for the simulation of GaAs MESFET´s with static negative differential resistance.