Why can't diodes with built-in potential be used as batteries?

  • Thread starter yinx
  • Start date
  • Tags
    Potential
In summary, diodes have a built-in potential due to thermal energy, but it is not enough to establish forward current. It must be overcome by an external potential in order for current to flow. Additionally, the term "contact potential" refers to a different concept and does not contribute to the establishment of current flow in a diode.
  • #1
yinx
39
0
Hello,

i was wondering for 1N4001 diode or zener diode has some built in potential, why can't they be used as batteries? I have some diodes lying around and I tried connecting to an LED, but it doesn't light up.

I know this question seem dumb, any help will be appreciated!

thanks!
Yinx
 
Physics news on Phys.org
  • #2
yinx said:
Hello,

i was wondering for 1N4001 diode or zener diode has some built in potential, ...

Why do you believe they have "built in potential"?
 
  • #3
pantaz said:
Why do you believe they have "built in potential"?

doesn't diodes have built in potential (aka contact potential)??

yinx
 
  • #4
The built in potential of a diode is a result of thermal energy. At a temp above absolute zero, 0K, the silicon crystal lattice vibrates. These vibrations have energy which separates electrons from the parent atoms leaving holes behind. This is thermal generation of electron-hole pairs, ehp.

The electrons, e-, & holes, h+, move through the Si & cross the junction. On the n-side of the junction, holes accumulate & recombine w/ electrons, vice versa on the p side. This accumulation of charges results in a local E field near the junction, & the integral of E over the distance is the potential.

In order to forward bias the diode, i.e. establish forward current, the built in potential must be considered. It has a polarity which tends to oppose current flow. The source powering the network must supply a potential large enough to overcome this potential.

A good semiconductor physics text covers this in detail. It has diagrams which make it clear. That should be where you look for your answers. If you need clarification on what I've said, that would be fine.

Claude
 
  • #5
Last edited by a moderator:
  • #6
The term built-in potential is frequently used in electronics and isn't contact potential.
Even though there is such a potential difference between the P and the N side, when we close a circuit no current flows. We feel disappointed but Thermodynamics feels very happy (if it were a person) because we haven't been able to get energy out of nothing.
When we consider a closed circuit we realize the built-in potential isn't the only potential difference to account for. When you do it properly, you end up with zero electro motive force around the circuit and no current flows.
However, we can build a thermal engine. Simply heat a thermocouple with a flame and close the circuit with another thermocouple submerged in ice water. You'll notice current flows and you get work as in any thermal engine.
 

FAQ: Why can't diodes with built-in potential be used as batteries?

What is the built-in potential of a diode?

The built-in potential of a diode is the potential difference between the p-type and n-type semiconductor materials that make up the diode. It is caused by the difference in doping levels between the two materials.

How is the built-in potential of a diode determined?

The built-in potential of a diode is determined by the doping concentrations of the p-type and n-type materials, as well as the temperature of the diode. It can also be calculated using the Shockley diode equation, which takes into account the diode's physical properties and operating conditions.

What is the significance of the built-in potential in a diode?

The built-in potential is an essential characteristic of a diode as it determines the diode's ability to conduct electricity in one direction. It creates a barrier that prevents the flow of current in the reverse direction, allowing the diode to act as a one-way valve for electrical current.

Can the built-in potential of a diode be changed?

The built-in potential of a diode is determined by the materials and their doping concentrations, so it cannot be changed once the diode is manufactured. However, by applying an external voltage, the diode's built-in potential can be overcome, allowing current to flow in the reverse direction.

What are the effects of temperature on a diode's built-in potential?

As temperature increases, the built-in potential of a diode decreases. This is due to the change in the bandgap energy of the semiconductor materials as temperature changes. A decrease in built-in potential can lead to an increase in reverse current flow, making temperature a critical consideration in diode design and operation.

Similar threads

Replies
10
Views
2K
Replies
1
Views
1K
Replies
6
Views
1K
Replies
14
Views
1K
Replies
2
Views
473
Replies
10
Views
2K
Replies
9
Views
2K
Back
Top