Home Uncategorized SEMICONDUCTOR - Band Theory, Silicon, Types

SEMICONDUCTOR – Band Theory, Silicon, Types

Semiconductor is not completely insulator nor completely conductor allows current to flow in only certain conditions. This quality of semiconductor makes it unique and useful. They don’t allow to flow the current in normal condition but, if we give them the energy required to free the electrons then they act as a conductor.

INDEX

  1. What is a Semiconductor?
  2. Semiconductor and Vacuum Tube
  3. Examples of Semiconductors
    1. Elemental Semiconductors
    2. Compound Semiconductors
  4. Band Theory
  5. Types of a Semiconductors
    1. Intrinsic Semiconductor / Pure Semiconductor
    2. Extrinsic Semiconductor
  6. Why silicon is preferred over germanium?
  7. Application of a Semiconductor
  8. Conclusion
  9. FAQs

What is a Semiconductor?

Silicon semiconductor Wafer
Silicon Wafer | image: commons.wikimedia.org

Conductors (silver, copper, gold) allows the current to flow easily. while, insulators (glass, plastic, wood) don’t allows the current to flow. But, semiconductor is not completely insulator nor completely conductor allows current to flow in only certain conditions. This quality of semiconductor makes it unique and useful.

They don’t allow to flow the current in normal condition but, if we give them the energy required to free the electrons then they act as a conductor.

All the diodes and transistors are made of semiconductor. Therefore, semiconductors are extremely important. Almost every computer, machines and robots are available to us because of the semiconductors.

Michael Faraday was the first person who observed the semiconductor effect in 1833. Before semiconductors invention, Other machines and calculators were working with help of vacuum tubes. It work was similar to diodes but, there was so many limitation in vacuum tubes.

SEMICONDUCTOR - Band Theory, Silicon, Types

Vacuum Tubes and Semiconductors

Vacuum TubesSemiconductors
Heavy bulky in sizeSmaller Size
High power consumption Very low power consumption 
Short lifespanLonger lifespan
Problem in creating vacuumNo need to create vacuum

However, Vacuum tube had many more problem there and semiconductor solved all these problems.

Examples of Semiconductors:

  1. Elemental Semiconductors
    • Silicon (Si)
    • Germanium (Ge)
  2. Compound Semiconductors
    • Gallium arsenide (GaAs)
    • Zinc selenide (ZnSe)
    • Silicon carbide (SiC).
    • Gallium nitride (GaN)
    • Indium phosphide (InP)

Band Theory

We are going to understand conductor, semiconductor, and insulator(non-conductor) with help of band theory.

So, let’s start…

band theory diagram
Band Theory | image: commons.wikimedia.org

The thing that is important for the current is free electron not valance electron(electrons in the last orbit of the atom). The place where all the free electrons exist is known as conduction band and the place where all the valance electrons exist is known as valance band However, the gap between them is known as forbidden energy gap.

Electrons in the conduction band are responsible for the flow of current. so, We have to give sufficient energy to the electrons in the valance band to cross the forbidden energy gap and jump to the conduction band.

As shown in figure, insulator has biggest forbidden energy gap therefore, we need to give very very high amount of energy. So, the electrons can jump in conduction band. But, that’s not possible practically. However, insulators can’t conduct current. But, in the case of conductors, there is no forbidden energy gap.

Their valance band and conduction band are over lapping because, they already have free electron at normal temperature. Therefore, we don’t have to give energy to the electrons and Electron can easily go to the conduction band without any external energy. However, conductors can easily conduct current and insulator can’t.

But, what about semiconductors? Because,their valance band and conduction band are not over lapping each other. So, they can’t conduct current in normal situation. But, its forbidden energy gap is not that large.

So, we can give sufficient energy to it, to jump the electron to the conduction band from valance band. This way semiconductor can act as an insulator and a conductor also. However, the forbidden energy gap of Silicon is 1.1ev and 0.78ev for Germanium at room temperature.

Types of a Semiconductors

  1. Intrinsic Semiconductor / Pure Semiconductor
    1. Silicon (Si)
    2. Germanium (Ge)
  2. Extrinsic Semiconductor
    1.  P-type semiconductor
    2.  N-type semiconductor

Intrinsic Semiconductor / Pure Semiconductor

You must be known to the America’s world famous city Silicon Valley”

World’s largest technology companies like Google, HP, Oracle, Apple and many more companies’ headquarters are held in Silicon Valley.

Silicon Valley’s name contain silicon which is a semiconductor.

Here are the two Intrinsic Semiconductors:

  1. Silicon (Si)
  2. Germanium (Ge)

However, Most of the Integrated Circuit maker prefer silicon over germanium as a semiconductor.

Why silicon is preferred over germanium?

The atomic structure of silicon and germanium are shown in the figure below:

Electron configuration of Germanium
Electron configuration of Germanium
Electron configuration of silicon
Electron configuration of Silicon
image: hyperphysics.phy-astr.gsu.edu

As you can see, Both of the atom of silicon(Si) and germanium(Ge) has 4 valance electron(electron in the last orbit). But, they are at different distance from the nucleus. The silicon’s atomic number is 14 so the valance electrons are in 3rd shell. While, germanium’s atomic number is 32. Therefore, its valance electrons are in 4th shell.

However, Germanium’s valance electrons have less attraction to the nucleus in compare to silicon’s valance electrons. Germanium’s valence electrons can easily be free electron because of less attraction even at the room temperature sometime. But, Silicon’s valence electron don’t go in the conduction band that easily. So, silicon’s atom is more stable at high temperature.

That is the reason why silicon is preferred over germanium.

Another reason of it is silicon is cheaper in compare to germanium. Because, silicon is found in sand.

Extrinsic Semiconductor

However, We can make Extrinsic Semiconductor by adding impurities into the intrinsic semiconductors. (This process is called doping) Doping is required because after doping, semiconductor has more free electrons or holes, so the flow of current and conductivity of semiconductor increases.

  • P-type semiconductor: If we add a trivalent impurity in a pure semiconductor which has 3 valence electrons, so a large number of holes will be created and current flow will be increased. P-type semiconductor has holes as a majority charge carrier.
silicon doped by trivalent impurity boron
silicon doped by trivalent impurity boron | image: commons.wikimedia.org

[ nh >> ne ]

Number of holes are far more than electrons in P-type semiconductors

Note that holes are just an absence of electron. Which wants an electron and electron has negative charge so, we have assumed holes as a positive charge.

Here are some examples of trivalent impurities

•Boron (B), Indium (In), Gallium (G), Aluminum (Al), etc.

  • N-type semiconductor: If we add a pentavalent impurity in a pure semiconductor which has 5 valence electrons, so a large number of a free electron will be created and current flow will be increased. N-type semiconductor has electron as a majority charge carrier.
silicon doped by trivalent impurity Phosphorus
silicon doped by trivalent impurity Phosphorus | image: commons.wikimedia.org

[ ne >> nh ]

So, Numbers of electrons are far more than holes in N-type semiconductors

Here are some examples of pentavalent impurities

•Phosphorus (P), Arsenic (As), Antimony (Sb), etc.

NOTE: P and N-type semiconductors are not positively or negatively charged, they are neutral. The N-type semiconductor just indicates that it has electrons as a majority charge carrier and P-type has holes. Electron denotes as negative sign and holes are just an absence of electron so it denotes as a positive sign. Therefore, it’s called as P-type and N-type. (Here P stands for positive and N for negative)

Application of a Semiconductors

computers on desk
Electronic devices | image: flickr.com

Semiconductors are used in

  • 3D printers
  • Transistors
  • Fire Alarm
  • Self-Driving cars
  • Computers
  • Robots
  • Integrated Circuits
  • Light Emitting Diode (LED)

Semiconductors are used in almost every electronic device!

Conclusion

In summary, the fact that semiconductor devices have unique characteristics such as low power consumption, high resistance to temperature, high breakdown voltage, and better thermal stability, as well as high mobility of electrons make them more applicable, especially in aerospace industry.

FAQs

1. What is semiconductor explain?

semiconductor is a substance, usually a solid chemical element or compound, that can conduct electricity under some conditions but not others, making it a good medium for the control of electrical current. 

2. What is the function of a semiconductor?

semiconductor can help controlled flow of electricity. The basic function of such a device is to switch ON and OFF the flow of electricity as and when required. A semiconductor device can perform the function of a vacuum tube with hundreds of times its volume

3. What is semiconductor in simple words?

semiconductor is a material that in some cases will conduct electricity but not in others. Good electrical conductors, like copper or silver, easily allow electricity to flow through them.

4. What are the advantages of semiconductor?

Compared to vacuum tubes, semiconductor devices always need a low operating voltage. Because semiconductors are small in size, the circuits involving them are also very compact. Unlike vacuum tubes, semiconductors are shock-proof. Moreover, they are smaller in size and occupy less space and consume less power.

5. Is gold a semiconductor?

Gold, symbol Au, is a soft metallic element that is bright yellowish in color. A good conductor of heat and electricity, it is also the most malleable and ductile of all metals. Gold is used in many aspects of semiconductor manufacturing, particularly in the assembly or packaging processes.

Hi, I’m a Blogger & Web-Developer.
Done B.tech from Dharmsinh Desai University, Nadiad

Viraj Mahida
Hi, I'm a Blogger & Web-Developer. Done B.tech from Dharmsinh Desai University, Nadiad
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