In this unit, we will get familiar with a variety of sources available for CHARGE simulations.
Source objects can be added to the simulation by clicking on the corresponding buttons in
the Sources section under the CHARGE tab.
Once added they will appear under the CHARGE solver object in the Objects Tree.
The bulk generation source object allows the user to define a simple analytical charge
carrier generation model with in the bulk of a semiconductor material due to solar absorption.
It is most commonly used to model optical generation in solar cells as it includes built-in
solar spectrum data needed for generation rate calculation.
The location and size of the object can be adjusted in the geometry section.
The direction of illumination can be chosen by picking one of the six sides of the cubic
The solar spectrum of choice can be selected from the spectrum option.
The AM1.5G solar spectrum is the most common spectrum used.
The material within which the optical generation happens should also be selected in order for
the object to correctly calculate the generation rate based on material properties.
In addition, the reflection from illumination face at the interface between air and semiconductor
can also be modeled.
If not selected, the surface is assumed to have no optical loss due to reflection.
A plot of the generation rate versus position or depth into the semiconductor layer will
be generated on the bottom right corner of the window.
For a more realistic solar cell simulation, a separate optical simulation is required
to obtain the optical generation within the semiconductor.
The Import optical generation source object allows importing a user defined optical generation
region with spatially varying generation rate.
This allows importing optical generation calculated from light absorption in optical simulations
using optical solvers such as FDTD or DGTD.
The location and dimension of the object will be determined by the imported data and x,y,z
values can be used to move the data to other locations.
By default, the generation object will be applied to all the simulation domains overlapping
with the defined geometry of the object.
Users have the option to select specific domains or solid objects that they want the optical
generation to get applied to.
In this case, other areas overlapping with the geometry of the generation object will
not have any optical generation assigned.
This feature can be used to define non-box shaped optical generation profiles.
Furthermore, by default, the geometry is defined with respect to the global coordinates origin
However, by enabling the relative coordinates options, users have the option to take the
center of the simulation region as origin for the convenience of geometry definition.
Under the Data tab, the file containing the optical generation data can be specified.
The file must be in Matlab format (.mat extension) and data can be defined over a rectangular
or a finite element mesh grid.
The unit for the imported generation data should be per cubic meter per second.
For an example of importing optical generation using this object, please visit the related
The scale factor option can be used to increase or decrease the amount of generation rate
by a multiplying factor for calibration purposes.
A value of 1 for scale factor means that the original values in the imported data will
The delta generation source object models the optical generation as a delta function
to create a point source.
This can be used for example in measuring the Internal Quantum Efficiency of photosensitive
For step by step instructions on how to use this object for measuring internal quantum
efficiency of a CMOS image sensor, please visit related links below.
In the source properties window, the location of the point where optical generation occurs
and also the generation rate as the number of electron hole pairs generation per second
can be specified.
The temperature import source object allows the definition of a spatially varying temperature
profile within the simulation.
This object can only be used in non-isothermal CHARGE simulations to account for the effect
of temperature on material properties and device performance.
The geometry settings are same as the import generation source and under the Data tab,
the file containing the temperature data can be specified.
The file must be in Matlab format (.mat extension) and data can be located over a rectangular
or finite element mesh grid.
The unit for the imported temperature data should be degrees Kelvin.
Similarly, The heat import source object allows the definition of a spatially varying heat
generation profile within the simulation.
This object can only be used in coupled HEAT and CHARGE simulations to account for the
effect of heat generation on material properties and device performance.
The geometry settings and data format are same as the temperature import source object
and the data should be in the units of watts per cubic meter.
In the next unit, we will discuss different monitor objects used in charge simulations.