Gunn Diode

diodeex07.in : Gunn Diode

Requires: DevEdit/Blaze
Minimum Versions: Atlas 5.28.1.R

This example shows the transient oscillatory behavior of a Gunn device due to the negative differential resistance of behavior exhibited by GaAs (as a result of electron intervalley transfer).

In the first part of the input file the structure is defined within DevEdit. The device is a sandwich structure made up of 2 gold electrode layers on the top and bottom, one low doped transit layer in the middle and 2 high doped layers acting as low resistivity contact regions and carrier injectors.

The thickness of the transit layer together with the applied electric field is one of the key design features determining the frequency of the oscillations.

In the second part of the file, after the 'go atlas' statement, transient device simulations are performed for different biases.

After loading the structure from DevEdit, a load resistor is attached at the anode side with the contact statement. In order to model the negative differential velocity saturation behavior for electrons, fldmob in the model statement is specified together with the evsatmod=1 parameter. This switches on the negative differential mobility model for GaAs like materials. As the function of holes is negligable, the solution of the hole continuity equation can be disabled by specifying carriers=1.

By ramping up the bias of the anode to 2 V one can clearly see the effect of the negative resistance extract is used to calculate the critical electric field from the log-file. With the following stationary simulation it can be shown that the bias is not sufficient to feed an oscillation with the given load, the oscillation is damped. The frequency is calculated by extracting the time required of 4 full periods.

In contrast, the device is able to operate at 4V bias. To monitor the movement of the domains, select several of the different electron distributions from different points in time (as 2d contours or the corresponding cutlines) displayed with TonyPlot at the end of the simulation, and make a movie using the Tools: Movie menu.

To load and run this example, select the Load button in DeckBuild > Examples. This will copy the input file and any support files to your current working directory. Select the Run button in DeckBuild to execute the example.