# Band Gap and Semiconductor Current Carriers | Intermediate Electronics

In this video, we are going to discuss about
band gap and semiconductor current carriers, which will help us understand how current
is produced in a semiconductor. If we recall some basic topics in chemistry,
we’ll remember that all atoms consist of neutrons, protons, and electrons, except for
a normal hydrogen atom which doesn’t have a neutron. Using the Bohr model, we can visualize that
an atom has a central nucleus consisting of protons and neutrons that is surrounded by
orbiting electrons. The orbits surrounding the nucleus are grouped
into energy levels known as shells and the outermost shell is called the valence shell. The valence shell of an atom represents a
band of energy levels, which is why it’s also called a “valence band” and valence
electrons are confined to that band. When a valence electron gains enough energy
from an external source, it can escape from the valence band and goes to the conduction
band. Band Gap
The difference in energy between the valence band and the conduction band is called “band
gap”. It is the amount of energy a valence electron
must possess so that it can jump from the valence band to the conduction band, wherein
the electron is free to move throughout the material. If the band gap is really big, electrons will
have a hard time jumping to the conduction band, which is the reason of material’s
poor conductivity. Energy Diagrams
Let’s try to examine the energy diagram of the three types of materials used in electronics
and discuss the conductivity of each material based on their band gap. As we can see, the band gap between the valence
band and conduction band in an insulator is really big. That is why it doesn’t conduct current. The band gap in a semiconductor is smaller
compared to an insulator and allows valence electrons in the valence band to jump into
the conduction band if it receives external energy. In a conductor, like copper, there’s no
band gap. Actually, the conduction band and valence
band overlaps, which means that electrons can freely move into the conduction band. This is why you may hear the electrons in
metal referred to as a “sea of electrons” – they’re just floating around. Current Carriers
Now that we know more about band gap, let’s discuss the two types of current carriers
in a semiconductor, free electrons and holes, and see how they produce current in a semiconductor. Atoms may combine to form a solid crystalline
material through covalent bonding. For example, a silicon atom covalently bonds
with four adjacent silicon atoms to form an intrinsic silicon crystal. Intrinsic because it doesn’t contain impurities
and a crystal because there is a pattern in how the atoms are connected. Electron Current
At room temperature, intrinsic silicon crystal gains enough heat energy that enables some
of the valence electrons to jump into the conduction band, becoming free electrons. When this happens, vacancies are left in the
valence band within the crystal. These vacancies are known as holes. Now, if we put a voltage source across an
intrinsic silicon material, the thermally-generated free electrons in the conduction band will
be attracted to the positive end of the voltage source. They will move toward the positive end and
this movement produces current in the material. This type of current is called electron current. Hole Current
While electron current happens in the conduction band, the other type of current, hole current,
happens in the valence band. Remember that as valence electrons jumped
into the conduction band, vacancies or holes are left in the valence band. Electrons that remain in the valence band
can move into a nearby hole when it receives a small amount of energy. This movement produces a current in the valence
band called hole current. Though the current is produced by valence
electrons moving into a nearby hole, it is called hole current so that it won’t be
confused with the electron current produced in the conduction band. In this video, we learned about band gap and
the current carriers in a semiconductor. We examined the energy diagram of the three
types of materials used in electronics, insulators, semiconductors, and conductors and briefly
discussed their conductivities. We also talked about the two types of semiconductor
current carriers, free electrons and holes, and mentioned how they produce current in
a semiconductor material. If you have any questions, leave it in the
comments below and if you’ve found this interesting or helpful, please subscribe to
our channel and like this video!

## 16 comments on “Band Gap and Semiconductor Current Carriers | Intermediate Electronics”

1. Nigel Kelly says:

Great explanation, thank you!

2. Jennifer Napoles says:

You did such an awesome job at describing this! I appreciate these videos and hope you do more in the future! 😀

3. Eunice K Na says:

Thank you!!!

4. DANIEL HOYOS CASTILLO says:

Por favor, sigue haciendo vídeos. Son muy útiles.

5. Deivyd says:

pff

6. Tawn Pham says:

Thank you for such a clear explanation! Straight to the point

7. Abdelrahman Hosny says:

clear and direct <3

8. VidBoii says:

I cannot describe how happy i am to understand this just before my exam. Thank you so much.😄

9. RRPA Chelses FC says:

😘😘😘

10. Sergio Ferreira says:

If I send to you the subtitles translated to Portuguese (BR) can you insert in this vídeo? Its really great, must important to share Knowledge

11. Skip Hoffenflaven says:

Perfection.

12. HairlessWookie OfHoth says:

Subscribed and liked bro good vid… I already know a bit about band Gap and transparency, just trying to refresh. Came across a vid about it from an English bloke and he was explaining with plastic balls from a kids play place… I found your vid right after.. you ever notice that Brits are smarter and more informed than the average person here, but I think that our best of the best outshine over here

13. Granit Mehmeti says:

Very helpful explanation. Thanks!

14. ぎんた says:

0:59
I think
Right→to jump from the conduction band to valence band

15. Soulimane Mammar says:

Nice!! I'm wondering… those free electrons in the conduction band are they jumping from atom to atom or still orbiting there original atoms??

16. Soulimane Mammar says:

Nice!! is the hole current observable as it is the case for conduction band current?