GaN HEMT Breakdown

ganfetex02.in : GaN HEMT Breakdown

Requires: Blaze
Minimum Versions: Atlas 5.22.1.R

This example demonstrates simulation of avalanche breakdown an AlGaN/GaN HEMT. It

This example is based on the paper:

Karmalkar and Mishra "Enhancement of Breakdown Voltage in AlGaN/GaN High Electron Mobility Transistors Using a Field Plate", ED 48, No. 8, pp 1515-1521, August 2001.

At the outermost level, the simulation uses the DeckBuild looping and variable assignment capabilities of LOOP, L.END and SET. Near the end of the input deck, the simulation again uses the built-in capabilities of DeckBuild to perform complex parameter extraction using the EXTRACT statements.

This Atlas part of the example demonstrates:

  • Construction of the heterojunction structure using Atlas syntax
  • Material and models parameter specification
  • Simulation of Id-Vds and breakdown characteristic
  • Display of the results in TonyPlot

The device under consideration consists of a simple 0.4 micron gate length GaN HEMT augmented with a field plate used to increase the breakdown voltage. This simulation loops on increasing field plate lengths to examine the relationship between field plate geometry and breakdown voltage.

In the first part of the input file, the device is described using the Atlas structural syntax. The description includes the mesh, regions locations, electrodes locations, and doping distribution. The region statements are used to define the AlGaN and GaN regions. The Al composition fraction (x.composition=0.295) is defined here as well.

After the device description, material statement are used to define the characteristics of the various materials used in the simulation.

The models statements are used to specify the following set of models : field dependent mobility, SRH recombination and Fermi-Dirac statistics.

In order to simulate avalanche breakdown, the impact ionization-generation model should be turned on. This is done using the impact selb statement in which the Selberherr impact ionization model is activated. All basic impact ionization parameters are user-accessible and can be modified by the user.

The gate electrode in HEMT structures is a Schottky contact. This is specified by using the contact statement to define the workfunction of the gate electrode.

Here the beam statement is used to specify an optical source of carrier pair generation in addition to the thermal generation provided by SRH. This is generally a good strategy for analyzing breakdown especially in wide bandgap materials or at low temperatures to improve convergence. This is not recommended when estimating sub-breakdown diode leakage currents though.

Next the drain voltage is ramped to 1200 volts. At that point the drain boundary is changed to a current boundary using the contact current statement.

This is performed to improve convergence up throught the breakdown portion of the curve where current is changing much faster than voltage.

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