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

Find the approximate bandwidth of the circuit, Q. An op amp has an open-loo...

Q. An op amp has an open-loop frequency response as shown in Figure. (a) Find the approximate bandwidth of the circuit using this op amp: (i) With a closed-loop voltage gain

Magnetic circuits with air gaps, The creation of a magnetic field in a ring...

The creation of a magnetic field in a ring may need to be accessed by means of an air gap. This is typically used to apply the magnetic field to a current carrying conductor to pro

Sketch the circuit with all the relevant labelling, Question: (a) Consi...

Question: (a) Consider the subsequent LC impedance function: (i) If the function is to be realised using the Foster I Form, evaluate the values of the different compon

Find dispersion relation for free electron, Find Dispersion Relation for Fr...

Find Dispersion Relation for Free Electron Question: Find the dispersion relation for a free electron, and, thus, observe the relation between its rest mass and effective ma

Define the term paging unit, Define the term Paging Unit. Paging Unit:...

Define the term Paging Unit. Paging Unit: The paging mechanism functions along with 4K - byte memory pages or along with a new extension obtainable to the Pentium with 4M byt

Amplifiers with feedback, Q. Amplifiers with Feedback? Almost all pract...

Q. Amplifiers with Feedback? Almost all practical amplifier circuits include some form of negative feedback. The advantages gained with feedback may include the following: •

#choke coil, #what is the procedure of the choke coil experiment

#what is the procedure of the choke coil experiment

Two-winding distribution transformer, Q. A single-phase, 10-kVA, 2300:230-V...

Q. A single-phase, 10-kVA, 2300:230-V, 60-Hz, two-winding distribution transformer is connected as an auto transformer to step up the voltage from 2300 V to 2530 V. (a) Draw a s

Find the decibels of improvement in signal-to-noise ratio, If a compressor ...

If a compressor in a system can change a message crest factor from 3.2 to 2, while maintaining its peak amplitude constant, find the decibels of improvement in signal-to-noise rati

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