Choosing between solvers and charge models in the 'Advanced' tab of DEVICE



The advanced tab in DEVICE offers users two different solvers, Newton and Gummel. Each of these solvers have their strengths and weaknesses and should be chosen depending on the simulation at hand.

In steady state (DC mode), Gummel solver is numerically faster compared to the Newton solver however, it becomes less reliable when the current flown in the system is large. Thus, for simulations under reverse bias conditions where the current flow is restricted, the Gummel solver should be chosen. However, when the device is in forward bias and the current flow is large, the Newton solver must be chosen. In transient simulations, the Newton solver must be used in all situation…

The advanced tab also allows user to choose between Fermi statistics and Boltzmann statistics in describing the charge distribution inside the semiconductor materials. Use of the Boltzmann statistics makes it easier for the solver to calculate the charge density (the integration over energy can be solved using analytic functions). However, it is only valid if the Fermi level is far away from the conduction and valence bands or in other words if the semiconductor is undoped or lightly doped. If the semiconductor is heavily (degenerate) doped then Boltzmann statistics is no longer valid and the used must use Fermi statistics.