Extrinsic material, Electrical Engineering

Assignment Help:

Extrinsic Material

  • In addition to thermally generated carriers, it is possible to create carriers in the semiconductor by purposely introducing impurities into the crystal => doping.
  • Most common technique for varying the conductivity of semiconductors.
  • By doping, the crystal can be made to have predominantly electrons (n-type) or holes (p- type).
  • When a crystal is doped such that the equilibrium concentrations of electrons (n0) and holes (p0) are different from the intrinsic carrier concentration (ni), the material is said to be extrinsic.
  • Doping creates additional levels within the band gap.
  • In Si, column V elements of the periodic table (e.g., P, As, Sb) introduce energy levels very near (commonly 0.03-0.06 eV) the conduction band.
  • At 0 K, these levels are filled with electrons, and very little thermal energy (50 K to 100 K) is required for these electrons to get excited to the conduction band.
  • Since these levels donate electrons to the conduction band, they are referred to as the donor levels.
  • Thus, Si doped with donor impurities can have a significant number of electrons in the conduction band even when the temperature is not sufficiently high enough for the intrinsic carriers to dominate, i.e., n0>> ni, p0 => n-type material, with electrons as majority carriers and holes as minority carriers.
  • In Si, column III elements of the periodic table (for example, B, Al, Ga, In) introduce energy levels very near (commonly 0.03-0.06 eV) the valence band.
  • At 0 K, these levels are empty, and very little thermal energy (50 K to 100 K) is required for electrons in the valence band to get excited to these levels, and leave behind holes in the valence band.
  • Since these levels accept electrons from the valence band, they are referred to as the acceptor levels.
  • Thus, Si doped with acceptor impurities can have a significant number of holes in the valence band even at a very low temperature, i.e., p0>> ni, n0 =>, p-type material, along with holes as majority carriers and electrons as minority carriers.
  • The extra electron for column V elements is loosely bound and it can be liberated very Easily => ionization; thus, it is free to participate in current conduction.
  • Similarly, column III elements create holes in the valence band, and they can also participate in current conduction.
  • Rough calculation of the ionization energy can be made based on the Bohr's model for H2 atoms, considering the loosely bound electron orbiting around the tightly bound core electrons. Thus,

    1536_Extrinsic Material.png

Where εr is the relative permittivity of Si.


Related Discussions:- Extrinsic material

Electrical machine -i, What are the causes of sparking in the commutator? E...

What are the causes of sparking in the commutator? Explain the methods to reduce the sparking in the commutator?

Relationship between the induced e.m.f and the network, Mathematical relati...

Mathematical relationship between the induced e.m.f and the network Faraday noted that the e.m.f induced in a loop is proportional to the rate of change of magnetic flux by it:

Define time constant, Time constant Time constant, defines as time for ...

Time constant Time constant, defines as time for current achieve maximum (IM) if this maintain the early promotion rate current.

Sketch the spectrum of a standard am signal, If the message has a spectrum ...

If the message has a spectrum where K and Wf are positive constants, sketch the spectrum of a standard AM signal that uses the message. Comment on the physical signi?cance

Zener diode, how does a zener diode works

how does a zener diode works

Software defined radio and modulation recognition, As we all know the next ...

As we all know the next century demand for wireless technology is expected to be the commercial implementation of Software Defined Radio (SDR) paradigm to improve base station effi

Name the flag bits available in 8085 microprocessors, Name  the flag bits a...

Name  the flag bits available in 8085 microprocessors. The 8085 microprocessor has five flags to show  five different  types  of data conditions .they are zero(Z),carry(CY),Sig

Calculate the magnitude of fault current, Figure shows an isolated three-ph...

Figure shows an isolated three-phase load supplied from a 33 kV/11 kV substation via a 30 km long three-phase 11 kV overhead line. The overhead line has the following series parame

Find a local s-matrix for each triangle, Figure shows two first-order trian...

Figure shows two first-order triangular finite elements used to solve the Laplace equation for electrostatic potential.  Find a local S-matrix for each triangle, and a global S-mat

Describe about reduction clause, Q. Describe about Reduction Clause? Re...

Q. Describe about Reduction Clause? Reduction clause specifies an operator as well as one or more list items. For every list item a private copy is created on every thread and

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd