# A question about setting up diffusion doping

I’m trying to simulation a pn junction along (the center of) a waveguide. If I know the lateral straggle of my dopant, and the location of junction (e.g. the center of the WG), how am I supposed to set up the parameters using diffusion doping? More specifically, how do I choose the doping region boundary and the junction width? What is difference between Gaussian and erfc?

Regards,

Chuan

Hi @chuan.xie,

Sorry for the delay, looks like we missed your post!

I am not an expert in DEVICE, but I think a good starting point is the p-n junction diode getting started example and the Mach-Zender modulator example.

Regarding the settings of the diffusion doping profile, the junction width defines the distance between the edge of the doping region (where we set the reference concentration) and the central part (as shown in the picture below) where the peak concentration is set.

The distribution function defines the actual distribution profile (either gaussian or complementary error function, erfc).

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