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Simulating Metal-Semiconductor Junction using SILVACO TCAD

  1. Dec 24, 2014 #1

    Sorry if it is too specific. I could not find a more specific group in the site. Would really appreciate if someone who has come across this already can find me a clue.

    I stumbled upon a strange result while playing with SILVACO TCAD, to simulate a metal semiconductor junction.

    I made a Metal-GaN structure (1D, nearly, along horizontal direction: x,) [GaN thickness along x was 6.4 micron (just to keep consistency with an experimental result) and the electrode was 0.4 micron on either side of the sample. The dimension along the vertical downward direction: Y, was 100 microns.]

    GaN was doped to a level of 1E14

    There was no work function specified at electrode: manual calls this an ohmic contact
    Expected consequences:
    i) No charge transfer: The semiconductor and the metal electrode remain charge-neutral: no band bending.
    ii) Voltage should be zero in both of them

    During simulation I had to use "solve init" command, which forced the electrodes on either side to assume a voltage of zero volts. That should not change the situation, since the voltage should have been already zero in absence of any charge transfer.

    After simulation of the zero volt situation I found that there was a constant potential inside GaN (about +1.428 V) with respect to the metal electrode.

    The doubt is: If there are no net charges in semiconductor & electrode, why should there be any potential in either of them?

    Manual [version release date: Feb 2012] says this voltage is the actual electrostatic potential as in Poisson’s equation [‘ψ ’ in page 102, referring to eqn. 3.1 in Page 96: ∇. (ε ∇ψ) = - ρ]. I was wondering where is this potential coming from?

    The magnitude of the potential happens to be the same as the Fermi energy shift [divided by the electronic charge] due to doping in GaN. Is it possible that the doping-induced change in Fermi level is assumed to be due to an increase in voltage? In that case, when we require the true electrostatic potential, should we subtract the doping induced Fermi level shift from the simulated value of the potential?

    Please let me know if you have come across this. I am attaching the image of the str file and the potential cut-line [horizontally through the middle of the sample, 50 micron deep, from the top].

    If you know of an existing thread on this, please do let me know.

    Thanks in advance

    Attached Files:

  2. jcsd
  3. Dec 29, 2014 #2
    Thanks for the post! This is an automated courtesy bump. Sorry you aren't generating responses at the moment. Do you have any further information, come to any new conclusions or is it possible to reword the post?
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