HEMT structure (High Electron Mobility Transistor)

Input files:
  • HEMT_1D_nnp.in

  • HEMT_2D_nnp.in

  • HEMT_3D_nnp.in

Scope:

This tutorial demonstrates how High Electron Mobility Transistors can be modelled with nextnano++.

HEMT structure

Input file: HEMT_1D_nnp.in

The structure consists of the following material layers:

width [nm]

material

1

Schottky barrier 0.2 eV

2

10.0

\(In_{0.532}Ga_{0.468}As\)

3

25.0

\(Al_{0.477}In_{0.523}As\)

4

50.0

\(In_{0.532}Ga_{0.468}As\)

5

300.0

\(Al_{0.477}In_{0.523}As\)

6

300.0

InP

The conduction band edge profile without doping is plotted in Figure 2.5.14.1.

../../../_images/1DHEMT_no_doping.jpg

Figure 2.5.14.1 Calculated conduction band edge profile.

Now we add at x = 35 nm a silicon delta doping of 4.5 \(\cdot\) 1012 cm-2 which leads to band bending. Instead of choosing a delta doping we specify a constant doping of 1.5 \(\cdot\) 1020 cm-3 that extends over 0.3 nm. (1.5 \(\cdot\) 1020 cm-3 \(\cdot\) 3 \(\cdot\) 10-8 cm = 4.5 \(\cdot\) 1012 cm-2)

We obtain two eigenstates and their corresponding wave functions inside the HEMT channel which leads to a two-dimensional electron gas (2DEG), see Figure 2.5.14.2. The electron density is plotted in blue.

../../../_images/1DHEMT.jpg

Figure 2.5.14.2 Calculated conduction band edge profile and probability densities.

In the file bias_00000/total_charges.txt we can find the integrated electron and hole densities. The total integrated density (from 10 nm to 100 nm) which can be measured experimentally is 1.87 \(\cdot\) 1012 cm-2 in agreement with the experiment. Most of the density is located between 45 nm and 95 nm.

2D/ 3D simulations

Input files: HEMT_2D_nnp.in, HEMT_3D_nnp.in

Input files for the same HEMT structure as in 1D, this time for a 2D and 3D simulations, are also available.

  • 2D: rectangle of dimension 250 nm x 10 nm

  • 3D: cuboid of dimension 250 nm x 10 nm x 10 nm