Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Band bending versus band sloping

  1. Jan 4, 2015 #1
    I'm trying to reconcile how a built-in potential can form in a semiconductor heterojunction in which there is a significant band cliff to majority carrier diffusion from both sides of the junction i.e. there is a cliff which should block hole diffusion from the p-type as well as a cliff which block electron diffusion from the n-type. There ought to be a significant Fermi level offset and there are countless publications of such systems exhibiting rectifying behavior. The problem also extends to a scenario in which there may not be a band cliff but there are insufficient free carriers available for depletion e.g. an i-n or an i-p diode.

    My assumption so far is that depletion need not necessarily occur for a built in potential to form and that band-sloping rather than band bending occurs instead - there is still a built in potential but there is no space-charge region (or, more generally, the space charge region does not wholly account for the built in potential) cf Fig 1b of this paper: http://pubs.acs.org/doi/abs/10.1021/jp300397f.
    Contrary to this, most analytic derivations for built in potential, depletion width etc derive these quantities from the space charge density using Gauss' law. This is even the case for p-i-n junctions, in which a substantial part of the junction has sloped rather than bent bands.

    My question is simply: Am I missing anything abvious? Is the idea of a band-slope built in potential physically sound?

  2. jcsd
  3. Jan 9, 2015 #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?
  4. Jan 14, 2015 #3
    Thanks for the bump. I can try to word it more simply, my original post is a bit of a mouthful. Here goes...

    p-n junctions form because electrons and holes diffuse across the junction, causing the regions either side to be depleted of charge. All the behavior associated with p-n diodes stems from this occurrence. So.....what happens when there is a barrier/cliff/discontinuity in the bands that should block the electrons and holes diffusing? How does the junction still form?
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook