Understanding the Function of a PN Junction Diode | Explained by Experts

In summary: When we apply a forward voltage Vf to the diode, we are actually pushing an electron from the anode into the cathode. This increases the potential difference between the two junctions.
  • #1
laxclarke
1
0
Say we have a silcon pn junction (diode) - i.e., a block of p-type on
left, attached to a block of n-type semiconductor on right:


anode ------[ p | n ]------ cathode


Because of diffusion we get a barrier potention at the junction, which
makes the n-side/cathode 0.7V higher than the p-side/anode:


~~~~~~~~ - 0.7V +

anode ------[ p | n ]------ cathode (*)


1) Now is there any way to "measure" this potential difference right
from the diode using some instrument?


Now to get ride of the depletion layer (barrier) we need an "opposite"
external voltage equal in magnitude to the 0.7V shown in (*) :


~~~~~~~ (barrier potential)
~~~~~~~ - 0.7V +
anode ------[ p | n ]------ cathode


~~~~~~~ + 0.7V -
~~~~~~~ (external voltage)


2) Now, why isn't the resulting voltage of the diode 0V (sum of
barrier and external)? How come we only measure the external 0.7V
using a voltmeter when the diode is forward biased?


3) Is there anything wrong with the thought process I've outlined
above?
 
Engineering news on Phys.org
  • #2
The instrument to measure is a voltmeter, or for more accurate results you can use a scope (only when the diode is on).

Correction: Because of diffusion the electron-hole paris recombine and a depletion layer is formed. To overcome this depletion layer an external potential (generally 0.7V for Silicon) is needed, hence you measure 0.7V and not 0V.

Once the depletion layer is formed it prevents the further recombination of holes and electrons.
 
Last edited:
  • #3
laxclarke said:
Say we have a silcon pn junction (diode) - i.e., a block of p-type on
left, attached to a block of n-type semiconductor on right: anode ------[ p | n ]------ cathode Because of diffusion we get a barrier potention at the junction, which
makes the n-side/cathode 0.7V higher than the p-side/anode: ~~~~~~~~ - 0.7V +

anode ------[ p | n ]------ cathode (*) 1) Now is there any way to "measure" this potential difference right
from the diode using some instrument?
unplebeian said:
The instrument to measure is a voltmeter, or for more accurate results you can use a scope.

Please note that it is not as simple as placing a voltmeter across the terminals of the diode and measuring the barrier potential, Vb. In fact one would expect a reading of zero volts. Give some thought to contact potentials. Remember that we have metal-metal and metal-semiconductor contacts.
 

1. What is a PN junction diode?

A PN junction diode is a semiconductor device that consists of a P-type semiconductor (with positively charged carriers) and an N-type semiconductor (with negatively charged carriers) joined together to form a junction. This junction allows the flow of electric current in one direction, making it a key component in electronic circuits.

2. How does a PN junction diode work?

A PN junction diode works by having a high concentration of electrons on one side (N-type) and a high concentration of holes (absence of electrons) on the other side (P-type). When a voltage is applied to the diode, it causes the electrons and holes to move towards the junction. This creates a depletion region, where there are no free carriers, preventing the flow of current in the reverse direction.

3. What are the applications of PN junction diodes?

PN junction diodes have a wide range of applications in electronic circuits. Some common uses include rectification (converting AC to DC), voltage regulation, and signal detection and mixing in radio and communication devices. They are also used in solar cells, LEDs, and photodiodes for light sensing.

4. What is the difference between a PN junction diode and a Zener diode?

The main difference between a PN junction diode and a Zener diode is their breakdown voltage. A PN junction diode has a high breakdown voltage and is used for rectification, while a Zener diode has a low breakdown voltage and is used for voltage regulation. Additionally, a Zener diode is designed to operate in the reverse breakdown region, while a PN junction diode is typically used in the forward bias region.

5. How can I test a PN junction diode?

There are a few ways to test a PN junction diode. One method is to use a multimeter in diode test mode to measure the voltage drop across the diode in forward and reverse bias. A good diode will have a low voltage drop in forward bias and a high voltage drop in reverse bias. Another method is to use a circuit with a battery, resistor, and LED to see if the diode lights up when connected in the correct direction. A defective diode will not light up in either direction.

Similar threads

  • Electrical Engineering
Replies
2
Views
874
  • Electrical Engineering
Replies
12
Views
1K
Replies
3
Views
706
  • Electrical Engineering
Replies
14
Views
2K
  • Electrical Engineering
Replies
7
Views
3K
  • Classical Physics
Replies
10
Views
1K
Replies
1
Views
805
Replies
1
Views
762
  • Electrical Engineering
Replies
8
Views
2K
  • Electrical Engineering
2
Replies
42
Views
8K
Back
Top