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This page contains detailed instructions on how to create the CHARGE project files.  Alternatively the project file provided in the top-level page can be used to go through the steps in the Results and Discussion page.

 

Material Database

Open a blank simulation file in CHARGE.  Under the Material section of the Design tab of the tabbed toolbar, click on the Electrical and Thermal button icon_electrical_thermal_material_zoom94 to open the Electrical/Thermal material database.  The CHARGE material database contains over 40 common Conductors (metals), Insulators (oxides), Semiconductors, and Alloys.  The properties of these materials can be edited and completely new custom material can be added to the database.  The "Material Properties" section in the material database has two (three for Semiconductors) tabs; Electrical Properties, Recombination (Semiconductor only), and Thermal Properties.  The Thermal Properties of a material is used by the HEAT solver only whereas the first (two) tabs contain material model applicable to the electrical solver (CHARGE) only.

 

gs_pndiode_cond_property_zoom50

Conductor Properties

Select "Al (Aluminium) - CRC" from the Material List. The only property of the metal that is relevant for electrical simulation using CHARGE is the work-function. The default value is set to 4.28 eV in the database. The work-function describes the energy-cost of removing an electron from the material and moving it to an infinite distance.

gs_pndiode_insulator_properties_zoom50

Insulator Properties

Even though we do not use any insulators in this example, we can take a quick look at the electrical material property of Insulators used by the CHARGE solver.  Select "SiO2 (Glass)" from the material list.  The insulator is defined only by its DC permittivity.  For SiO2 this value is 3.9.

gs_pndiode_semicond_property_zoom50

Semiconductor Properties

The models for the semiconductor require far more complex parametrization than those of a conductor or insulator. In this example, we will use a very simple model to describe the behavior of silicon.

Select "Si (Silicon)" from the Material List, and choose the 'Electronic Properties' tab.  The values for dc-permittivity and work function for silicon are set to 11.7 and 4.59 eV, respectively.  The value for the bandgap is set to 1.11452 eV by default.  This gives an intrinsic carrier concentration of approximately 1010 cm-3.

 

Temperature dependent models for many of the electrical properties of semiconductors are available.  To enable a model and set the appropriate coefficients, click on the editing button, e.g. icon_temp_dep_button_DEVICE (temperature dependence).  This action will bring up the model parameter editing dialog.  In this example, we will enable a temperature dependent band-gap model.  Click on the icon_temp_dep_button_DEVICE button in the 'Band Gap' properties group under the 'Fundamental' tab.  In the "Edit Model Parameters" dialog that appears, enable the model, and enter the coefficients as shown in the image below.  Note that the coefficients correspond to those in the equation displayed in the model parameter editor.  Once the coefficients are set as shown, close the dialog by pressing OK.  To visualize the temperature-dependent behavior, choose the “Visualize” option from bottom right corner of the Material Database window and select 'T' (temperature) as the first axis and check Eg (bandgap) as the result to be plotted.  Select the range of temperature from 100 K to 400 K.  Now clicking the 'Create Visualization' button should plot the temperature dependence of the band gap in a new window as shown below.

 

Editing the coefficients for the temperature-dependent band-gap model of silicon

Editing the coefficients for the temperature-dependent band-gap model of silicon

Visualization window inside the material database

Visualization window inside the material database

 

The resulting bandgap for silicon as a function of temperature

The resulting bandgap for silicon as a function of temperature

 

Click on 'Done' button to go back to material properties dialog. To complete the material setup, go to the "Mobility" tab under the "Electronic Properties".  Make sure that the "Impurity" scattering model is disabled (set to None).

 

Available mobility models for semicodnuctors in the material database

Available mobility models for semicodnuctors in the material database

 

This is a sufficient set of parameters to model the basic behavior of silicon. All other properties should be disabled. Other semiconductors can be treated similarly.  This step is now complete. The properties of the conductor (aluminum) and semiconductor (silicon) have been defined. Accept the changes by clicking OK, which closes the Material Database. Save the workspace as a new project from the "File" tab.  To be consistent with the provided project file, you can name the file pn_diode.ldev.

 

Materials

 

Si (Silicon) and Al (Aluminium) - CRC must be added from the database to the materials object (only electrical properties, thermal not needed) in Objects Tree. To do this you have two options:

 

1. Under the Materials section of the Design tab, click on New Material button icon_design_newmaterial_zoom94. Then right click on recently added New Material under the Material Group in Objects Tree and click on Add electrical properties. This will automatically open Electrical/Thermal Material Database. Scroll it down to find Si (Silicon) from Material List and click on Select. This will add the material as Semiconductor object that includes only electrical properties of Si (Silicon).

 

2. Click on the Electrical and Thermal button icon_electrical_thermal_material_zoom94 to open the electrical/thermal material database. Select Si (Silicon) and then click on Create button as is shown below:

 

gs_create_silicon_zoom60

 

This will add electrical (semiconductor) and thermal (solid) properties of silicon material into Objects Tree. After adding the properties, rename the new material to 'Si (Silicon)' by double clicking on its name or right click and then select rename. The same procedure should be followed to add Aluminum to the simulation.

 

 

Geometry

The Structures section of the Design tab icon_structures_tab_zoom64  can be used to introduce various types of structures into the simulation space.  The available options vary from simple rectangles and spheres to complex waveguides and planar solids.  In this example, we use three rectangles to define the substrate and the two metal contacts of the pn diode.

 

substrate

From the Structures section of the Design tab, select a RECTANGLE to be added to the Objects Tree. Select the rectangle in the Objects Tree and click on the "Edit Properties" button icon_edit to edit the properties of the rectangle according to the following table.

tab

property

value


name

substrate

Geometry

x (um) / x span (um)

0 / 2


y (um) / y span (um)

0 / 2


z (um) / z span (um)

-30 / 60

Material

material

Si (Silicon)

 

emitter

From the Structures section of the Design tab, select another RECTANGLE to be added to the Objects Tree. Select the rectangle in the Objects Tree and click on the "Edit Properties" button icon_edit to edit the properties of the rectangle according to the following table.

tab

property

value


name

emitter

Geometry

x (um) / x span (um)

0 / 2


y (um) / y span (um)

0 / 2


z (um) / z span (um)

1 / 2

Material

material

Al (Aluminium) - CRC

 

base

From the Structures section of the Design tab, select another RECTANGLE to be added to the Objects Tree. Select the rectangle in the Objects Tree and click on the "Edit Properties" button icon_edit to edit the properties of the rectangle according to the following table.

tab

property

value


name

base

Geometry

x (um) / x span (um)

0 / 2


y (um) / y span (um)

0 / 2


z (um) / z span (um)

-61 / 2

Material

material

Al (Aluminium) - CRC

 

Simulation Region

 

Click on icon_simulation_region in the Objects Tree and click the icon_edit button (on the left of the Objects Tree) to edit its properties according to the following table:

 

 

tab

property

value

General

dimension

2D Y-Normal


x min boundary

closed


x max boundary

closed


z min boundary

closed


z max boundary

closed

Material

background material

None

Geometry

x (um) / x span (um)

0 / 1


y (um)

0


z (um) / z span (um)

-30 / 61

 

 

 

CHARGE Solver Region

In the Solvers section of the Design tab select the icon_solver_charge_zoom88 to place a CHARGE solver in the simulation environment.  Note that once the solver is selected, all the simulation objects (i.e. Constraints, Doping, Source, Monitors) belonging to the CHARGE solver become available under a new tab named CHARGE.  Select the CHARGE object from the Objects Tree and click on the "Edit Properties" button icon_edit to edit the properties according to the following table.

 

tab

property

value

General

simulation temperature (K)

300


norm length (um)

10000

Mesh

Maximum edge length (um)

4


Minimum edge length (um)

0.01

Advanced

Poisson solver control

Check use defaults


Drift_Diffusion solver control

Check use defaults

 

Mesh Constraint

In Solver section under the CHARGE tab, press on the CONSTRAINT button icon_CHARGE_constraint to add a Electrical Mesh Constraint to the objects tree.  Select it from the Objects Tree (under CHARGE) and click on the "Edit Properties" button icon_edit to edit the properties according to the following table.

section

property

value


name

space charge layer

Geometry

x (um) / x span (um)

0 / 2


y (um) / y span (um)

0 / 2


z (um) / z span (um)

-20.5 / 2

Mesh Constraints

Maximum edge length (um)

0.1

 

Doping

The DOPING section under the CHARGE tab provides three different types of doping objects.  Two analytic doping objects (Constant, Diffusion) and one Import doping object that allows the user to import a custom doping profile from file.  In this example, to create a pn junction in the diode, we will dope the entire substrate with light n-type doping and then apply a heavy p-doping on one end.  Both these doping will be created using the constant type doping objects as described below.

 

nepi

From the DOPING section under the CHARGE tab, click on CONSTANT doping button icon_charge_doping_constant_zoom88 to add a Constant Doping Region object to the simulation. Select it from the Objects Tree (under CHARGE) and click on the "Edit Properties" button icon_edit to edit the properties according to the following table.

section

property

value


Name

nepi

Geometry

x (um) / x span (um)

0 / 5


y (um) / y span (um)

0 / 5


z (um) / z span (um)

-30 / 80

Dopant

Dopant type

n


Concentration

1e+15

 

pwell

From the DOPING section under the CHARGE tab, click on CONSTANT doping button icon_charge_doping_constant_zoom88 to add a Constant Doping Region object to the simulation Select it from the Objects Tree (under CHARGE) and click on the "Edit Properties" button icon_edit to edit the properties according to the following table.

tab

property

value


Name

pwell

Geometry

x (um) / x span (um)

0 / 4


y (um) / y span (um)

0 / 4


z (um) / z span (um)

-7.5 / 25

Dopant

Dopant type

p


Concentration

1e+17

 

Monitors

 

bandstructure monitor

We will add a 1D bandstructure monitor in our simulation region to easily view the band profile of the pn diode.  From the Monitors section under the CHARGE tab, click on the Band icon_CHARGE_monitor_band button to place a band structure monitor in the simulation domain. Select the monitor in the Objects Tree and click the icon_edit button to edit its properties according to the following table.

tab

property

value


name

band

General

monitor type

linear z

Geometry

x (um)

0


y (um)

0


z (um) / z span (um)

-30 / 80

 

Note: The z span of the monitor is made larger than that of the simulation region.  In such cases, the span of the saved data will be determined by the span of the simulation region.

 

charge monitor

We will add a 2D charge monitor in our simulation region to record the total charge in the silicon and its variation with bias voltage.  From the Monitors section under the CHARGE tab, click on the Charge icon_CHARGE_monitor_charge button to place a charge monitor in the simulation domain.  Select the monitor in the Objects Tree and click the icon_edit button to edit its properties according to the following table.

tab

property

value


name

charge

General

monitor type

2D y-normal


integrate total charge

Enabled

Geometry

x (um) / x span (um)

0 / 3


y (um)

0


z (um) / z span (um)

-30 / 70

 

Note: The x and z span of the monitor is made larger than that of the simulation region.  In such cases, the span of the saved data will be determined by the span of the simulation region.  Selecting the "integrate total charge" option automatically integrates the charge in the monitor region and provides the total charge as a result.

 

Boundary Conditions (Electrical Contacts)

To apply the required bias voltages to the device under investigation (pn diode) we will create two (electrical) boundary conditions to be added to the Boundary Conditions Group (available under CHARGE Solver object).  There are eight types of boundary conditions available two of which are supported by the CHARGE solver. These are Electrical and Surface Recombination boundary types which can be added from the Boundary Conditions section of the CHARGE tab as shown in the screen shot below.  

 

add_electrical_boundary_conditions_device_zoom75

 

emitter

Here we will create an electrical contact that will apply a bias voltage to the emitter object in the Objects Tree.  Add an Electrical boundary condition from the CHARGE tab. Select it in the Objects Tree and click the icon_edit button to edit its properties according to the following table.

tab

property

value


name

emitter

General

bc mode

steady state


force ohmic

true


sweep type

single


voltage (V)

0

Geometry

surface type

solid


solid

emitter

 

base

Here we will create another electrical contact that will apply a bias voltage to the base object in the Objects Tree.  Add an Electrical boundary condition from the CHARGE tab. Select it in the Objects Tree and click the icon_edit button to edit its properties according to the following table.

tab

property

value


name

base

General

bc mode

steady state


force ohmic

true


sweep type

single


voltage (V)

0

Geometry

surface type

solid


solid

base

 

The project file is now set up.  Save the file using the "File" menu and run it by following the instructions provided in the Results and Discussion page.

 

 

Small-signal AC Simulation Setup

In this section, we will modify the already set up (steady-state) project file to perform small-signal analysis.

 

CHARGE Solver Region

Select the CHARGE solver region from the model tree and click on the "Edit Properties" button icon_edit to edit the properties according to the following table.

 

tab

property

value

General

solver mode

ssac

Small Signal AC

perturbation amplitude (V)

0.001


frequency spacing

log


log start frequency (Hz)

1000


log stop frequency (Hz)

1e10


num frequency points per dec

3

Advanced

solver type

newton

 

Boundary Conditions

 

emitter

Select the emitter electrical contact and click the "Edit" button to edit its properties according to the following table.

tab

property

value

General

bc mode

Steady state


apply ac small signal

all


sweep type

range


start (V)

0


stop (V)

-2


interval (V)

-0.2

 

base

Select the base electrical contact and click the "Edit" button to edit its properties according to the following table.

tab

property

value

General

bc mode

steady state


sweep type

single


Voltage (V)

0

 

The project file is now set up.  Save the file using the "Save As" option in the "File" menu and change the name to ac_pn_diode.ldev.  Run the simulation by following the instructions provided in the Small-signal Analysis page.

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