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

What is button, A button does some command in a program when it is clicked....

A button does some command in a program when it is clicked. Buttons generally have a 3-dimensional look, although you may have to move the mouse over the button for it to look 3D.

Give the properties and application of cotton, Give the properties and appl...

Give the properties and application of cotton. Cotton : It is base material for insulating fibres. Properties: It can be enhanced by impregnating with varnish. 1)

Sketch the output waveform for the synchronous counter, Q. Consider a serie...

Q. Consider a series-carry synchronous counter with T flip-flops shown in Figure in which the AND gates carry forward the transitions of the flip-flops, thereby improving the speed

Superposition theorem, how do you work it out if there are 3 sources in par...

how do you work it out if there are 3 sources in parallel?

Stax store accumulator indirect instruction , STAX Store  Accumulator  In...

STAX Store  Accumulator  Indirect Instruction This  instruction is used to  copy data from accumulator to the memory  location pointed by register pair ( only  BC or DE pair).

Define capacitor construction, Define Capacitor Construction In its mo...

Define Capacitor Construction In its most elementary state a capacitor having of two metal plates separated by a certain distance d, in among the plates lies a dielectric mate

Calculate the fraction of particles - top plate, Consider a colloidal suspe...

Consider a colloidal suspension of latex particles confined between two plates. The plates are charged, so there is an electric potential difference V between them (as shown). The

Assembly languages - second generation language, Assembly Languages  ( Sec...

Assembly Languages  ( Second Generation Language) To overcome  the difficulty of machine  language assembly  language  was  designed. After  facing the  difficulty of machine

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