Jan 2017

Doping of Semiconductors

January 13, 2017

Do you know what doping of semiconductors refers to? No, it’s nothing illegal! By altering the behavior of the semiconductor, doping allows for some of the impressive properties of semiconductors to come to existence. Going for physics tuition with us will further deepen your understanding on semiconductors in Singapore.

What is doping?

Doping a semiconductor refers to the process of adding impurities to a semiconductor in order to alter its physical properties. This causes them to become one of two conductor types:

  • p-type [3 valence electrons, electron deficiency]
  • n-type [5 valence electrons, electron surfeit]

Octet rule

This rule states that an atom is stable with 8 valence electrons if not they are inclined to donate or accept atoms. Using silicon as an example, it is held in a lattice that shares an electron with its neighbor, therefore making everything stable.
If we ‘dope’ silicon with phosphorus, we will suddenly have a pentavalent atom- 5 valence electrons- added to the matrix. 4 of those electrons will share with the atoms around it, but one electron is left free. This electron is free to move, and you now have a conductive substance. You have created a negative, or n-type semiconductor
P-type or positive semiconductors basically work in reverse to this. It shares three atoms with the silicone around it but is left with a ‘hole’ where the 4th electron is missing. This leaves it ready to accept an electron at any point. Of course, it should always be remembered that the process is never 100% pure, there will always be unplanned impurities, but laboratories work hard to keep these to a minimum.

What is the simplest semiconductor device?

This would be a diode where it allows current to flow in one direction and has applications in devices such as turnstiles. A diode only allows conductivity one way- the other results in a dead circuit and no movement.

Why is this so effective?

Doping by adding impurities is incredibly effective because it’s highly controllable. Spatial variety is quite easy to create, especially with the controlled use of p-n junctions as well as manipulating inbuilt fields. This enables the creation of controlled dopant structures, part of which is why this technology is so useful for microcircuits and microchips.

What happens at different temperatures?

It is critical for most of these applications that the resulting product is stable and operational at a wide variety of temperatures. This means that a good understanding of the carrier density and properties as a function of temperature is very important. This is only part of what makes doping of semiconductors a convoluted and fairly difficult field of study. A detailed knowledge of the principals involved may not be needed for JC physics tuition, but if you wish to continue further do be prepared for some difficult learning and heavy use of formulas.
Semiconductors play a vital part in most modern electronics, and they have been instrumental in changing the way the world works. Getting to grips with these complicated principles is a critical part of preparing for your physics paper.

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