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Homework Help: Turn-on voltage of pn junction diodes

  1. May 2, 2009 #1
    Hey, im working on a report and got stuck at two discussion questions. Help & discussion would be greatly appreciated!

    1. What factors determine the turn-on voltage of a pn junction diode? Explain its dependence on the factors you mentioned

    My guess would be that the light intensity on the diode would affect it due to excitation of electrons which will affect the electron-hole recombination and hence the depletion region width? Im also betting on temperature and also doping concentrations. Temperature will cause a shift in the I-V characteristic, thus changing the turn on voltage but am not sure why? As for doping concentrations... it's really a wild guess.

    2. Explain the factors that influence the spectral linewidth of the emission spectrum.

    Really stumped by this! I'm thinking that different semiconductor materials will have different spectral linewidths but not really sure about the theoretical basis behind it. Apparently it can be adjusted?

    Thanks a lot in advance!
  2. jcsd
  3. May 2, 2009 #2
    This is definitely not introductory physics. Also, you might want to get a book on semiconductor processes or diodes because that question requires a lot of detail. You should look up the injection process under forward bias and see what affects it. Doping concentrations affect the Fermi level which is important in calculating the injection voltage as well as the band gap. But you will need a lot more reading and details to get a better understanding.
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