Hi I would like to ask something more about charge/mode, I will do it here (instead of opening a new thread). I try to do something similar as this example: PIN Mach-Zehnder Modulator. However, I want to see the change in neff in MODE at different currents (not voltage). Is there any way to change the boundary conditions into current instead of voltage?
Furthermore, when I use voltage higher than 2.5V the simulation does not converge. Is there any solution?

I attach you some images of my simulation
Charge layout and result:

MODE with the np density imported as an attribute:
Difference in refractive index:

It seems that the neff is not changing as in the example. I am unsure of how to define the GaN in MODE, I imported some data as sampled 3D data and then a created a new material based on Drude model. Should I do this or directly the refractive index is going to be defined in the NP attribute?