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

Dc chooper, Establish the relationship between duty ratio and output voltag...

Establish the relationship between duty ratio and output voltage

Hlt halt instruction , HLT Halt Instruction The microprocessor halts  ...

HLT Halt Instruction The microprocessor halts  the execution  of the  program and enters into  the wait  state  the address  and data bus are placed in the  high  impedance st

Externally initiated signals - pins and signals , Externally  Initiated Si...

Externally  Initiated Signals Other than  interrupt  there are followings externally initiated  signals  available in 8085 microprocessor.

Explain ferrites and its uses in high frequency devices, Explain ferrites a...

Explain ferrites and its uses in high frequency devices. A group of magnetic alloys show the property of magnetisation that change, with percentage of various constituent atoms

Determine a normalized frequency at 820nm, Determine a normalized frequency...

Determine a normalized frequency at 820nm for a step index fibre having 25µm core radius. Given n 1 =1.48 and n 2 =1.46.Also calculate how several modes propagate within this fibre

Diode circuits, Diode Circuits: Prob. (a) Draw the piecewise linear v...

Diode Circuits: Prob. (a) Draw the piecewise linear volt ampere characteristic of a p n diode. What are the circuit models for the ON state and the OFF state. (b) Determ

Define the dma controller interface, Define the DMA controller interface. ...

Define the DMA controller interface. A DMA controller interfaces along with a few peripherals which may request DMA. The controller chooses the priority of simultaneous DMA req

Compute force vector, Q. Consider a current element I 1 d ¯l 1 = 10 dz ¯a...

Q. Consider a current element I 1 d ¯l 1 = 10 dz ¯az kA located at (0,0,1) and another I 2 d ¯ l 2 = 5dx ¯ax kA located at (0,1,0). Compute d ¯F 21 and d ¯F 12 experienced by

Common base configuration - bjt, Common base configuration: for pap t...

Common base configuration: for pap transistor connection for common base operation is as follow: common base means base is common to both input and output side of configurati

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