Visualizing the Doping Profiles
The Semiconductor interface provides the built-in functionality to visualize doping profiles for the selected Analytic Doping Model or Geometric Doping Model feature. You can visualize doping profiles by clicking the preview buttons before solving the model. Two buttons named as Plot Doping Profile for Selected and Plot Net Doping Profile for All are available both in the toolbar and the context menu. The doping profile will be shown in a separate plot window named as Doping Profile Plot. Note that p-type and n-type domains are shown in red and blue color, respectively.
The Plot Doping Profile for Selected button visualizes the dopant concentration added by the selected doping feature. The added dopant concentration is defined as semi.<tag>.Na and semi.<tag>.Nd for acceptor doping and donor doping, respectively. The Plot Net Doping Profile for All button visualizes the absolute value of the net dopant concentration defined as |Nd-Na|.
Figure 2-6: Example of a net doping profile for the Application Library model 3D Analysis of a Bipolar Transistor.
 
The usage of the preview button for doping profiles is shown in the following library models:
Bipolar Transistor: Application Library path Semiconductor_Module/Transistors/bipolar_transistor
3D Analysis of a Bipolar Transistor: Application Library path Semiconductor_Module/Transistors/bipolar_transistor_3d
DC Characteristics of a MOS Transistor (MOSFET): Application Library path Semiconductor_Module/Transistors/mosfet
Trench-Gate IGBT 3D: Application Library path Semiconductor_Module/Transistors/trench_gate_igbt_3d
GaAs P–N Junction Infrared LED: Application Library path Semiconductor_Module/Photonic_Devices_and_Sensors/gaas_pn_junction_infrared_led_diode
Note that the plots for doping profiles generated by clicking preview buttons cannot be modified. However, it is also possible to create a customized doping profile. To do this, in the Study toolbar, click Get Initial Value (). Then add a plot group and display the corresponding dopant density. The signed doping concentration, semi.Nd-semi.Na (positive for net donor doping and negative for net acceptor doping), gives the net doping and can be useful for visualizing the effect of different doping steps. If multiple doping features are superimposed, it is possible to visualize the total dopant concentration or to display the contribution from individual doping features.
Study and Computing the Initial Values in the COMSOL Multiphysics Reference Manual.
The semi.Nd-semi.Na expression shows the total net doping due to the sum of all doping features. To see the distribution from a single doping feature the corresponding node tag must be included in the plot variable.
To select the node labels to display, on the Model Builder toolbar click Model Builder Node Label ().
The node tags are shown in curly brackets next to the nodes in the Model Builder. Analytic Doping Model features are tagged as adm# and Geometric Doping Model features are tagged as gdm#, where # corresponds to the number of the feature. The dopant concentration from each doping feature is available as semi.<tag>.Na for acceptor doping or semi.<tag>.Nd for donor doping. For example, semi.adm1.Nd for a donor distribution from the first Analytic Doping Model added to the component.