# 1D - Doping Functions¶

Attention

This tutorial is under construction

The sample input files for this tutorial are:

• basics_1D_doping_predefined.in

• basics_1D_doping_analytic.in

## Introduction¶

This tutorial is the fifth in our introductory series. In the previous tutorials, we’ve already encountered one pre-defined doping profile - the constant one. In the following, we will see more possibilities to create doping profiles. After completing this tutorial, you will know more about:

• different doping profiles, namely linear and Gaussian

• crating custom doping profiles

Keywords: Gaussian1D{}, linear{}, import{}

## Main¶

As an overview, Figure 2.5.1.17 shows all the structures that will be created in this turorial.

### 1. Using pre-defined doping profiles¶

In this example we demonstrate two pre-defined doping profiles, namely Gaussian and linear profiles. For that we consider the setup in Figure 2.5.1.17 (left). The associated input file is basics_1D_doping_predefined.in.

Specifying regions with dopants

37structure{ # this group is required in every input file
38    output_impurities{ boxes = yes}     # output doping concentration [10^18 cm-3]
39
40    #---------
41    # material
42    #---------
43
44    region{
45        binary{ name = GaAs }           # material: GaAs
46        contact{ name = whatever }      # contact definition
47        everywhere{}                    # region spreads over the complete device
48    }
49
50    region{
51        binary{ name = InAs }           # region: InAs
52        line{ x = [ 20.0, 30.0 ] }      # position: x=20.0 nm to x=30.0 nm
53    }
54
55    #-------
56    # doping
57    #-------
58
59    region{
60        line{ x = [ 30.0, 40.0 ] }      # position: x = 30.0 nm to 40.0 nm
61        doping{                         # add doping to the region
62            gaussian1D{                 # Gaussian doping concentration profile
63                name = "p-type"         # name of impurity
64                conc = 1.0E18           # maximum of doping concentration [cm-3]
65                x = 35                  # x coordinate of Gauss center
66                sigma_x = 1.0           # standard deviation in x direction
67            }
68        }
69    }
70
71    region{
72        line{ x = [ 0.0, 20.0 ] }       # position: x = 0.0 nm to 20.0 nm
73        doping{                         # add doping to the region
74            linear{                     # linear doping concentration profile
75                name = "p-type"         # impurity name
76                conc = [0, 6.0e17]      # start and end value of doping concentration [cm-3]
77                x    = [0.0, 20.0]      # position: x=0.0 nm to x=20.0 nm
78            }
79        }
80    }
81}

We seperated the structural set up in two sections: 1) material and 2) doping. In the doping section we use linear{} and gaussian1D{} to specify the doping profiles. For defining the Gaussian profile

$C_{gaussian}(x)= C_{conc}\frac{1}{\sigma\sqrt{2\pi}} \cdot e^{-\frac{1}{2}(\frac{x- x_0}{\sigma})^2}$

with the total doping concentration $$C_{conc}$$, coordinate of the maximum $$x_0$$ and standard deviation $$\sigma$$, three parameters has to be specified. For defining the linear profile

$C_{linear}(x) = \frac{ C_{end} - C_{start} }{ x_{end} - x_{start}} \cdot x + C_{start},$

we specify start and end value of doping concentration $$[y_{start}, y_{end}]$$ with the corresponding x coordinates $$[x_{start}, x_{end}]$$, both as vectors.

Specify impurity species

84impurities{ # required if doping exists
85    acceptor{                   # select the species of dopants
86        name = "p-type"         # select doping regions with name = "p-type"
87        energy = 0.045          # ionization energy of dopants
88        degeneracy = 4          # degeneracy of dopants
89    }
90}

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 2.5.1.18.

### 2. Using custom doping profiles¶

In this example we introduce custom defined doping profiles. For that we consider the set up in Figure 2.5.1.17 (right). The associated input file is basics_1D_doping_analytic.in

Defining custom functions

20import{ # this group is optional
21    analytic_function{                      # definition of analytic function
22        name = "custom_exp_fun_I"           # name of function
23        function = "1e18 *(1-exp(-x+20))"   # define the function
24    }
25    analytic_function{                      # definition of analytic function
26        name = "custom_exp_fun_II"          # name of fucntion
27        function = "1e18*exp(-x+30)"        # define the function
28    }
29}

In order to create custom doping profiles, we have to define analytical functions in the group import{} first. The analytical expression is given by a string. Later, we can incorporate these functions for adding doping by referring to the corresponding name.

Specifying regions with dopants

63structure{ # this group is required in every input file
64    output_impurities{ boxes = yes}                 # output doping concentration [10^18 cm-3]
65
66    #---------
67    # material
68    #---------
69
70    region{
71        binary{ name = GaAs }                       # material: GaAs
72        contact{ name = whatever }                  # contact definition
73        everywhere{}                                # region spreads over the complete device
74    }
75
76    region{
77        binary{ name = InAs }                       # region: InAs
78        line{ x = [ 20.0, 30.0 ] }                  # position: x=20.0 nm to x=30.0 nm
79                                                    # overwrites the previously defined GaAs region
80    }
81
82    #-------
83    # doping
84    #-------
85
86    region{                                         # region: adds doping
87        line{ x = [ 20.0, 30.0 ] }                  # position: x=20.0 nm to x=30.0 nm
88        doping{
89            import{                                 # reference to import{} group, where custom functions are defined
90                name = "n-type"                     # name of impurity
91                import_from = "custom_exp_fun_I"    # import doping profile: custom_exp_fun_I
92            }
93        }
94    }
95
96    region{                                         # region: adds doping
97        line{ x = [ 30.0, 50.0 ] }                  # position: x=30.0 nm to x=50.0 nm
98        doping{
99            import{                                 # reference to import{} group, where custom functions are defined
100                name = "n-type"                     # name of impurity
101                import_from = "custom_exp_fun_II"   # import doping profile: custom_exp_fun_II
102            }
103        }
104    }
105}

Inside doping{}, the previously defined functions are used to create custom doping profiles. We import each function (import_from) from the group import{} by referring to the name that we had assigned. The function is then evaluated on the interval specified inside line{} yielding the final doping profile.

Besides the shape of the doping profile we also specify the name, as usually.

Specify impurity species

108impurities{ # required if doping exists
109    acceptor{                   # select the species of dopants
110        name = "p-type"         # select doping regions with name = "p-type"
111        energy = 0.045          # ionization energy of dopants
112        degeneracy = 4          # degeneracy of dopants
113    }
114}

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_donor.dat) as shown in Figure 2.5.1.19.

## Important things to remember¶

• before importing and using our own functions, we first have to define them in the import{} group