Use the Analytic Trap Density node to specify the density of traps within the domain. This feature enables a density to be defined by an expression written in terms of the local coordinate system. Alternately, it enables a region of uniform trap density which decays into a background density with one of three preset profile functions to be created. The trap density can be used in conjunction with a Trap-Assisted Recombination feature to specify recombination via trapping sites whose density varies in space. The available options are similar to the Analytic Doping Model feature.

In some cases it is desirable to increase the trapping from zero or a low value to that required in the simulation during the solution process. This can improve the convergence of the problem significantly. The continuity settings allow the trap densities to be weighted by an external parameter whose value should be between 0 and 1. By default the Continuation type is set to Use interface continuation parameter. This means that the continuity settings are determined by the Doping and trap density continuation in the Continuation Settings section for The Semiconductor Interface. To introduce the trapping from a specific feature independently of the other features, select User defined and manually enter the Continuation parameter. This should be set to a dimensionless parameter that is swept from zero to 1 using the continuation solver.

To disable the continuation for a particular trapping feature select No continuation for the Continuation type. The effect of the traps can also be ramped on using the continuation feature within the trap-assisted recombination feature.

Select a Distribution — User defined (the default) or Box.

Select an Impurity type to give the conductivity type of the selected semiconductor material — Donor traps (the default), Acceptor traps, Neutral electron traps, or Neutral hole traps.

For any selection, enter a Trap density Nt0 (SI unit: 1/m3). The default value is 1 × 1016 1/cm3.

This section is available when Box is selected under Distribution. See Analytic Doping Model for these settings.

This section is available when Box is selected under Distribution. Select a Profile away from uniform region — Gaussian (the default), Linear, or Error function (erf).

By default, the Specify different length scales for each direction check box is not selected. It is possible to specify a different profile length scales in each coordinate direction when this check box is selected.