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

Phase shifter, Hi, I just finish writing my project literature review and ...

Hi, I just finish writing my project literature review and my supervisory asked me to add one part. This part is about Phase Shift. How phase shifters work? In Particular How the

RC phase shift oscillator, For the RC phase-shift oscillator if c=1pF and R...

For the RC phase-shift oscillator if c=1pF and R=10K determine the value of Rf

Metering techniques, Metering Techniques The techniques of metering co...

Metering Techniques The techniques of metering could be categorized depending upon the voltage at which consumers are fed as: 1. LT (Low Tension) Metering, and 2. HT (Hi

Corrosion, I want to know whether the circuits for both methods(linear pola...

I want to know whether the circuits for both methods(linear polarization resistance and electrochemical impedance spectroscopy) are same or not?

Give a general account of common drain amplifier, Q. Give a general account...

Q. Give a general account of common drain amplifier? The output is taken over the source terminal and when the dc supply is replaced by its short circuit equivalent, the drain

Define a voltmeter, Define a voltmeter A voltmeter is an instrument us...

Define a voltmeter A voltmeter is an instrument used to measure p.d. and must be linked in parallel with the part of the circuit whose p.d. is required.

Variations of drain current - drain voltage, Q. Consider the common-source ...

Q. Consider the common-source JFET circuit shown in Figure with ?xed bias. Sketch the sinusoidal variations of drain current, drain voltage, and gate voltage superimposed on the di

Phase equilibria, distinguish between brittle and ductile fracture

distinguish between brittle and ductile fracture

Issues for installation of meters, Issues for Installation of Meters T...

Issues for Installation of Meters The subsequent should also be ensured: a) Appropriate crimping device should be used for crimping the lugs. Thimbles should be of appro

Minimized circuit using or and and not gate, Given S(F) = A'B +'C'D + C'D +...

Given S(F) = A'B +'C'D + C'D +'A'B + 'A B + 'A 'C + 'A D + 'A C A. DRAW A MINIMIZED CIRCUIT USING ONLY OR AND NOT GATES (2 input gates) B. WRITE THE WIRE LIST Example of a

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