diode property

Discussion in 'General Electronics Chat' started by raks_universe, May 10, 2009.

  1. raks_universe

    Thread Starter Active Member

    Mar 15, 2009
    we know that barrier potential of si diode=0.7 eV

    when the silicon diode is heavily doped(ZENER) ,does the barrier potential remains the same or not ??
  2. mik3

    Senior Member

    Feb 4, 2008
    A zener diode is usually operated in reverse bias region and brakes down at certain voltages depending on its doping. Thus you don't mind about its forward region a lot. However, as the doping levels in a diode increase the barrier potential increases too.
  3. raks_universe

    Thread Starter Active Member

    Mar 15, 2009
    how does the barrier potential increases ??

    I think it will remain same.
    Only the electric field across depletion width increases due to decrease in depletion width (E=v/d).

    PLEASE explain clearly!!
  4. beenthere

    Retired Moderator

    Apr 20, 2004
  5. raks_universe

    Thread Starter Active Member

    Mar 15, 2009
    I can,t find the answer for my question.

    Don't consider zener diode ,consider ordinary si diode.

    Is doping concentration affects the barrier potential(voltage) ?
  6. DonQ

    Active Member

    May 6, 2009
    I think that you'll find that forward current (~60mV/decade) and temperature (about -1.8mV/°C) will be larger influences than doping levels. Current and temperature are things that you know or can easily measure, but I have never seen doping levels listed in the specs.
  7. AdrianN

    Active Member

    Apr 27, 2009
    No, it does not. The potential barrier is given by the following relation:

    Vb = VT * ln (Na*Nd/ni^2)

    where VT = kT/q = 26 mV at 300 degK, Na and Nd are the doping concentrations for acceptors and donors respectively, and ni is the intrinsic concentration for a pure semiconductor.

    Therefore, when Na and Nd change, Vb changes and that is why Vb can have a range around 0.65V, depending on the manufacturer process. Because of the T (temperature) dependence, Vb has large variations with the temperature as well.

    Although Na and Nd can vary drastically from a process to another one, due to the logarithmic function in the Vb formula that variation is "small". So, even if the impurity concentration increases say, ten times, Vb increase can be of around 40 mV.
    Last edited: May 11, 2009
  8. David Bridgen

    Senior Member

    Feb 10, 2005
    The forward voltage of a zener is about the same as a signal or rectifier diode.

    If you connect an ohmeter across a zener such that it is forward biased, the meter will indicate a fairly low resistance - just like any other diode.

    If you connect the ohmeter so that a zener is reverse biased it will indicate a much higher resistace, as one would expect.

    If you use a digital meter with a diode range on it, the indication when the diode is forward biased is very often a measure of the forward voltage at whatever current the meter makes its measurement.
    On my meters the indications are a little less than 0.7.