— FREE — Constant Doping

Header

Files for the tutorial located in nextnano++\examples\basics

• basics_1D_doping_constant_p.in

• basics_1D_doping_constant_np.in

Introduction

This tutorial is the third in our introductory series. We want to show the general framework of adding doping to material regions in nextnano++. After completing this tutorial, you will know more about

• adding doping to material regions

• specify the species (donor/ acceptor)

Keywords: doping{}, impurities{ }, donor{}, acceptor{}

Overview

As an overview, Figure 2.4.10 shows the two structures that will be created in this tutorial.

Figure 2.4.10 shows p-doped GaAs (left) and p-doped/ n-doped GaAs (right).

The Basics I: Adding doping to bulk material

As an introductory example to doping, we want to n-dope a single GaAs layer as shown on the left of Figure 2.4.10. You can use the template input file basics_1D_doping_constant_p.in.

Specifying regions with dopants

structure{ # this group is required in every input file
    output_impurities{ boxes = yes}             # output doping concentration [10^18 cm-3]

    region{
        binary{ name = GaAs }                   # material: GaAs
        contact{ name = whatever }              # contact definition
        everywhere{}                            # rangeing over the complete device, from x=0.0 nm to x=50.0 nm

        doping{                                 # add doping to the region
            constant{                           # constant doping concentration profile
                name = "Custom_impurity_name"   # name of impurity
                conc = 1.0e18                   # doping concentration [cm-3]
            }
        }
    }
}

First of all, we create just one thick GaAs layer. Then we add doping to the exact same region by the specifier doping{}. Inside doping{}, we have to set the doping profile. Here we choose to have constant doping concentration over the whole region. Inside constant{} we specify name and doping concentration (conc) for this region. The name is arbitrary, and you can choose whatever name you like. By giving the doping a reference name, we can select the species and electronic properties for this doping later inside the group impurities{ }.

Since we want to inspect the doping concentration distribution for every grid point in the output, the flag boxes = yes inside output_impurities{ } is active.

Specify impurity species

impurities{ # if doped regions exist, this group is required
    acceptor{                           # select the species of dopants
        name = "Custom_impurity_name"   # select doping regions with name = "Custom_impurity_name"
        energy = 0.045                  # ionization energy of dopants [eV]
        degeneracy = 4                  # degeneracy of dopants
    }
}

If dopants are added to any region, the group impurity{} has to be included in the input file. acceptor{} sets the species for regions with name “Custom_impurity_name”. We further refine the properties by setting ionization energy (energy) and degeneracy level (degeneracy).

Output

We simulate the device by clicking F8 on the keyboard. In the related output folder you should find a plot of the concentration profile (\(\Rightarrow\) Structure \(\Rightarrow\) density_acceptor.dat) as shown in Figure 2.4.11.

Figure 2.4.11 shows the doping concentration of acceptors along the x direction.

The Basics II: Adding different doping to bulk material (p-n junction)

As another introductory example, we n-dope the first half and p-dope the second half of the single GaAs layer as in Figure 2.4.10 (right). Now, the doping regions do not coincide with the material regions. We have to define material and doping regions separately. You can use the template input file basics_1D_doping_constant_np.in.

Specifying regions with dopants

structure{ # this group is required in every input file
    output_impurities{ boxes = yes}     # output doping concentration [10^18 cm-3]

    region{
        binary{ name = GaAs }           # material: GaAs
        contact{ name = whatever }      # contact definition
        everywhere{}                    # ranging over the complete device, from x=0.0 nm to x=50.0 nm
    }

    region{                             # separate region for adding doping only (no material is specified)
        line{ x = [ 0.0, 25.0 ] }       # position: x=0.0 nm to x=25.0 nm
        doping{                         # add doping to the region
            constant{                   # constant doping concentration profile
                name = "p-type"         # name of impurity
                conc = 1.0e18           # doping concentration [cm-3]
            }
        }
    }

    region{                             # separate region for adding doping only (no material is specified)
        line{ x = [ 25.0, 50.0 ] }      # position: x=25.0 nm to x=50.0 nm
        doping{                         # add doping to the region
            constant{                   # constant doping concentration profile
                name = "n-type"         # name of impurity
                conc = 1.0e18           # doping concentration [cm-3]
            }
        }
    }
}

In the code above, we first create a bulk GaAs layer and then add two doping regions for n-type and p-type dopants. The doping regions do not include a material specification. Inside these regions, the position (line{}) and the doping (doping{}) is specified. The dopants are added to the previously defined material region. In fact, this example illustrates that, as far as the initialization is concerned, nextnano++ treats doping and materials separately.

Specify impurity species

impurities{ # if doped regions exist, this group is required
    donor{                  # select the species of dopants
        name = "n-type"     # select doping regions with name = "n-type"
        energy = 0.045      # ionization energy of dopants
        degeneracy = 2      # degeneracy of dopants
    }
    acceptor{               # select the species of dopants
        name = "p-type"     # select doping regions with name = "p-type"
        energy = 0.045      # ionization energy of dopants [eV]
        degeneracy = 4      # degeneracy of dopants
    }
}

As we already know if dopants are added, the group impurity{} has to be included in the input file. Apart from acceptor{}, we introduce donor{} as another doping species. For both species we refine the properties here.

Output

We simulate the device by clicking F8 on the keyboard. In the related output folder you should find a plot of the concentration profiles (\(\Rightarrow\) Structure \(\Rightarrow\) density_acceptor.dat / density_donor.dat) as shown in Figure 2.4.12 and Figure 2.4.13.

Figure 2.4.12 shows the doping concentration of acceptors along the x direction (p-doped region).

Figure 2.4.13 shows the doping concentration of donors along the x direction (n-doped region).

Important things to remember

• dopants are part of a region, i.e. structure{…region{…doping{}…}…}. Here you determine the concentration of one impurity type for each grid point.

• The impurity type (species and properties) are defined inside the group impurity{}

Last update: 16/07/2024