Polarization Charge Analysis

ganfetex01.in : Polarization Charge Analysis

Requires: Blaze
Minimum Versions: Atlas 5.22.1.R

This example demonstrates the interaction between polarization charges, surface states and cap layer thickness in AlGaN/GaN HFETs.

This example was the basis for the Simulation Standard article "Simulating the Source of Polarization Charge in AlGaN/GaN HFETs" Simulation Standard, V. 15, N. 8, Aug. 2006, Silvaco International.

This article and example are based on the work of: J. P. Ibbetson, et. al., Appl. Phys. Lett. 77, 250 (2000).

The input deck ganfetex01.in uses dbinternal to obtain the channel charge density for each of the saved structure files. It does this using the file ganfetex01_aux.in. The advantage of using dbinternal is that the data file containing the charge densities can be plotted using TonyPlot. These charge densities are plotted against the cap layer thickness.

The input deck containing the actual description of the devices is contained in ganfetex01_aux.in.

The Atlas specification consists of the following parts:

  • Construction of the device and the grid using Atlas syntax
  • Specification of material regions
  • Definition of electrodes and doping
  • Material, models, interface charge and interface trap parameters
  • Simulation of Id-Vds characteristic

In the first part of the input file the device is described using Atlas syntax including mesh, regions and electrodes locations, and doping distribution. The region statements are used to define AlGaN and GaN regions. The Al composition fraction (x.composition=0.34)is defined here as well. After the device description, the material statement is used to specify some of the material parameters different from the default values. Whenever any of the default values of material parameters or models are questioned you should specify the parameter values manually.

The model statement is used to specify the following set of models: field dependent mobility, and Shockley-Read-Hall recombination, Fermi-Dirac statistics, and incomplete ionization.

Next the interface characteristics are specified. In particular the polarization charges and surface traps are specified. We could have used the built-in polarization models that calculate the polarization charges as a function of composition, strain and lattice constant for the various materials, but in this case we are specifying polarization charges directly to simplify calibration to the data presented in the paper.

Next the solve statement is used to obtain a zero biassed solution. The save statement is used to save this solution for subsequent examination in TonyPlot. TonyPlot is used to look at the channel electron charge as a function of cap layer thicknress.

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.