Si substrate thickness of plasmonic solar cell


I am trying to work on plasmonic solar cell. I have read plasmonic solar cell part of knowledge base and also run the .fsp file of plasmonic solar cell given on the KB.
I have some questions:

  1. what is the thickness of the Si absorber layer (in the .fsp it is named as ‘substrate’)? which field defines the Si thickness…x span? y span? or z span?..or anything else?

  2. what should I do if I want to take a Si substrate with 3 micrometer thickness?

  3. I noticed in the .fsp file, the ‘bottom_monitor’ is placed bellow 0.5um from the top surface. what is reason behind this? To measure the bottom surface transmission if I want to place a bottom monitor at the bottom level of the Si substrate (thickness 3um), where should I place the monitor?

  4. I also want to know about the position of ‘FDTD’ simulation region. specifically its geometrical settings. What is the relation between the Si substrate thickness and position of FDTD simulation region?

Your suggestions would be very helpful for me.

Hi @ariful,

You can also look at the other solar cell examples (including the getting started one).

Regarding your questions:

If you look at the simulation, you can see that the plane wave is propagating along the z axis. The thickness of the substrate object is defined by its z span and/or z min/z max.

In the simulation, the thickness is 2um. To change it to 3um you need to change “y min” to -3um. If you change “z span”, it will move the upper interface.

As you noticed, the simulation doesn’t cover the whole Si thickness, but only 800nm. I can see 2 reasons for this:

  1. Most of the absorption occurs in that region.
  2. It allows you to define a smaller simulation and, therefore, the calculation will be shorter.

If you want to include the whole Si thickness, you need to increase the size of the FDTD region so its bottom boundary is below the Si interface. This setting is used in the getting started example I mentioned earlier. You may also need to increase the simulation time:

The simulation time should be long enough for the fields to decay and reach the auto-shutoff criteria, as explained in this discussion.