Why do the free electrons in the N-type want to diffuse?

In summary, when making a diode, impurities called electron acceptors are added to the P-type semiconductor and electron donors are added to the N-type semiconductor, creating a concentration gradient that causes diffusion of free electrons from the N-type to the P-type. This process is known as doping and is explained in the book Electronic Principles by Albert Malvino.
  • #1
SaruMihai
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I'm trying to understand how a diode works and for this I've used(among other resources) the book written by Albert Malvino, Electronic Principles.

Everywhere I read about this topic, it says that when the N-type and P-type semiconductors are joined together, the free electrons from the N-type diffuse to the P-type.

I don't understand why is the diffusion happening.

The book Electronic Principles contains an attempt to explain this and states that the electrons diffuse because they have the same charge and they repel each other, but in my understanding the P-type and the N-type semiconductors have a neutral charge, because the number of positive charges (protons in the nuclei) is equal to the number of negative charges (free electrons and covalent bonds electrons), so the electrons repeling each other can't actually be the cause of the diffusion.
 
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  • #2
When making a P-type, impurities called electron acceptors are added to the material (look up 'doping'). These ions capture free electrons from the surrounding material, leaving behind 'holes' - spaces that may be filled with electrons. In an N-type, electron donors are added which provide free electrons to the surrounding material. So the P-type has a high concentration of holes but not many free electrons, and the N-type has a high concentration of free electrons but not many holes. Hence when the two are put in contact we have a concentration gradient and diffusion occurs.
 

1. What is an N-type semiconductor?

An N-type semiconductor is a type of material that has been doped with impurities to increase the number of free electrons. This results in a material that has a higher concentration of negative charge carriers, making it a good conductor of electricity.

2. Why do N-type semiconductors have free electrons?

N-type semiconductors have free electrons because they have been doped with elements such as phosphorus or arsenic, which have more valence electrons than the atoms of the base material. These extra electrons become free to move around the material, making it conductive.

3. How do the free electrons in N-type semiconductors move?

The free electrons in N-type semiconductors move through a process called diffusion. This is when particles, in this case electrons, move from an area of high concentration to an area of low concentration in order to create a more even distribution of charge.

4. What causes the free electrons in N-type semiconductors to diffuse?

The free electrons in N-type semiconductors diffuse because of the concentration gradient created by the doping process. This means that there is a higher concentration of electrons in the doped area compared to the undoped area, causing the electrons to move and diffuse throughout the material.

5. Why is the diffusion of free electrons important in N-type semiconductors?

The diffusion of free electrons is important in N-type semiconductors because it allows for the conduction of electricity. As the free electrons move throughout the material, they create a flow of current, making it useful for electronic devices and circuits.

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