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Why diode voltage is 0.7V?

### Author Topic: Why diode voltage is 0.7V?  (Read 2907 times)

#### tiagoft

• Newbie
• Posts: 2
##### Why diode voltage is 0.7V?
« on: March 27, 2011, 11:32:50 AM »
Hello, all

Just a question (I have not found an answer for this elsewhere...):

The voltage of a silicon diode is 0.7V. This depends on many factors, including the geometry of the PN junction. My question is: there is a certain range of acceptable values for that geometry. Why the geometry that gives that 0.7V was chosen?

Tiago

#### Hero999

• Global Moderator
• Electronics God
• Posts: 2774
##### Re: Why diode voltage is 0.7V?
« Reply #1 on: March 27, 2011, 02:29:08 PM »
Thye voltage is dependant on the temperature, current and materials.

0.7V wasn't chosen, it's due to the band gap of silicon. Germanium has a lower bandgap so the forward voltage is much lower 0.3V.

Here's a link to an experiment you can do yourself.
http://www.phys.csuchico.edu/~eayars/publications/bandgap.pdf

#### nolram11

• Newbie
• Posts: 2
##### Re: Why diode voltage is 0.7V?
« Reply #2 on: September 12, 2011, 11:10:45 PM »
The forward-biased (junction) voltage for silicon diodes is 0.7V in most of the circuit analyses, but it can dip to as low as o.6V because of the construction of diodes is not perfect. As for germanium diodes, yes it's 0.3V when forward-biased.

#### dlhylton

• Newbie
• Posts: 1
##### Re: Why diode voltage is 0.7V?
« Reply #3 on: January 25, 2012, 08:38:59 AM »
The voltage drop is just based on the material used, not so much the other factors.

Silicon= 0.7v drop
Germanium= 0.3v drop

-David