Hi. The bulk generation object is for silicon and CdTe only. It uses a simple 1D analytic model to get the generation rate profile for solar illumination. The delta optical generation on the other hand is used to model an impulse in the generation rate.
The main “generation rate” source is the “import optical generation” object. In most cases in order to get the generation rate profile of a device you need to perform an optical simulation (using an optical solver like FDTD Solutions). You can the use the “import optical generation” object to import this profile into DEVICE.
If you would like to calculate the generation rate in your device using analytic equation, you can also do that. Use the script in DEVICE (or use an external software like Matlab) to calculate the bulk generation rate G at each grid point defined by vectors x, y, and z. Then import the data into DEVICE using the “import optical generation” object. You will have to save the coordinates (x,y,z) and the generation rate (G) in a .mat file which you can load in the source.
To learn how you can load generation data into the “import optical generation” object, check out this other post: How to import data into the import generation object?