Enhancement Mode IEMOSFET I-V and Breakdown Curves

Requires: Blaze, TFT

Minimum Versions: Atlas 5.28.1.R

This example is based on the following paper submitted by "4.3 m-ohm.cm2, 1100 V 4H-SiC Implantation and Epitaxial MOSFET", Shinsuke Harada et al., Material Science Forum Vols. 527-529 (2006) pp 1281-1284.

The paper investigated the effect of a Nitrogen implant in the surface of the lightly doped drain region, that was the electrical N-type doping connection to the main vertical drift region to the back of the device where the drain contact resides. In order to allow users to experiment with this n-type doping concentration, this concentration was defined as a variable called "CN" near the beginning of the input file. In the example, this doping concentration was set to the near-optimal value of 1e17/cm³.

For large band-gap semiconductors, it is necessary to use extended precision when simulating the device in the "off" condition, such as when simulating breakdown. In this example, 160-bit precision is used, which is defined in the "go atlas" statement at the beginning of the input file. For the simulation of the I-V curves, it is not strictly necessary, however, but it is still used here for completeness.

The "mesh" startement defines the width of the device. In order to convert the simulated currents into Amps/cm² used in the paper, the 1.5 um gate length device needs to be multiplied by 6.67e7 um.

One of the features of the SiC/oxide interface is the very high density of interface states under the gate, which dominates the determination of the threshold voltage. Most publications place the typical interface state density as high as 1e14/cm²/eV at the band edges, dropping to a near-constant value of 2e11/cm²/eV throughout the rest of the band gap that is more than 0.5eV away from each of the band edges. These interface states are modelled using the "intdefects" statement.

The high density of interface states effectively turns off the channel, naturally creating a normally off (enhancement mode) device with a high threshold voltage. In order to reduce the threshold voltage to the more acceptable 3.4 volts required for this paper, an n-type channel implant is required, with a surface concentration as high as 1.2e17/cm³ as specified in the paper. Using this surface implant specified in the paper and the distribution of interface states found in the open literature, the correct threshold voltage of 3.4 volts was obtained.

Finally, very tight tolerances are applied to the solution using the "method" statement, which forces the simulator to resolve currents down to approximately 1e-30 amps, which is necessary to accurately account for leakage currents.

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.