Queation on electron concentration expression

1

Hi everyone,

I have a question regarding the electron concentration expression in DEVSIM. In the provided examples like diode1d and bjt, the node model elec_i, which represents the electron concentration, is set as n_i * exp(Potential / V_t). However, I believe the expression should be n_i * exp((Potential - phi_n) / V_t), where phi_n represents the quasi-Fermi potential for electrons.

Could anyone clarify if my understanding is correct and why the difference exists?

Thanks in advance!

2

The expression mentioned is in the definition of function CreateSiliconPotentialOnly(device, region).

3

Hi @Wong,

If I remember correctly for this script:

For the potential only solution, the Fermi level is flat, and assumed to be 0. The Potential is tied to the intrinsic Fermi level. So:

E_{F_n} = E_{F_p} = 0\\ \psi = - E_{F_i}/q

This would not work for a system with multiple materials, so the scripts would need to be modified accordingly.

Please let me know if you think there is still an error or if I made a mistake in the discussion above.

5

Thank you for your reply. I’ve figured out the issue, and it turns out the script is correct.

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