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Zapping a semiconductor with a laser

  1. May 7, 2008 #1
    If you zap a n-type semicond. with a laser with energy at, say, the band gap, what happens to the donor electrons? For sake of argument, let's say we're at low temp. where the occupation of electrons on donors is high. I know technically, you should only get transitions at the energy of the laser (top of vb to bottom of cb), but do you think that in reality the donor electrons (if shallow enough) would be ripped from their impurity sites? And then 'reattach' after a equilibrating time.
    Does anyone know what happens?
  2. jcsd
  3. May 14, 2008 #2
    Based on experimental results at RT with a CW dye laser at 600 nm (~1.5 eV) the electrons at the Si 2p level moved ~1.2 eV while the laser was turned on at the same time that an XPS instrument with its X-ray beam was measuring the Si 2p signal. GaAs responded similarly but with a lower shift.
  4. May 17, 2008 #3

    The 2p level is the donor level? What is an XPS instrument and what does it mean to measure the Si 2p signal?
  5. May 17, 2008 #4
    Based on current thinking the 2p does not contribute significantly to the donor level. But it does interact with the donor level and all other levels through "configuration interaction".

    If you visit Wikipedia, you can find the XPS article that I am the main author of. It may help. The technique sends X-rays (1486 eV) into a sample. The X-rays interact with the atoms and electrons near the surface that have less than 1486 eV of binding energy will come out into the ultra-high vacuum of the instrument.

    The Si 2p signal indicates that the 2p electrons have ~100 eV of binding energy. The Si 2s occurs at 150 eV. The Si 3s occurs at ~8 eV and the Si 3p occurs at ~3 eV. The 3s and 3p electron levels are the main contributors to the donor level. Then there are the free electrons etc.
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