diode property

Thread Starter

raks_universe

Joined Mar 15, 2009
67
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 ??
 

mik3

Joined Feb 4, 2008
4,843
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.
 

Thread Starter

raks_universe

Joined Mar 15, 2009
67
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!!
 

DonQ

Joined May 6, 2009
321
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.
 

AdrianN

Joined Apr 27, 2009
97
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 ??
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:

David Bridgen

Joined Feb 10, 2005
278
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.
 
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