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

Microprocessor, Write a program to count how many from your data set called...

Write a program to count how many from your data set called MYDATA, which is a set of signed single-byte numbers, has positive value and are odd numbers. Save the result in POSOD

Determine the flux densities, In the magnetic circuit shown in Figure (a) t...

In the magnetic circuit shown in Figure (a) the coil of 500 turns carries a current of 4 A. The air-gap lengths are g 1 = g 2 = 0.25 cm and g 3 = 0.4 cm. The cross-sectional are

RC coupled transistor amplifier., why we plot graph to find bandwidth is dr...

why we plot graph to find bandwidth is drawn b/w av/avmax v/s frequency not av v/s frequency?

Semiconductor, What is the similarities between a vacuum diode and a triode...

What is the similarities between a vacuum diode and a triode?

Serial input output ports , Serial Input output Ports For serial  inpu...

Serial Input output Ports For serial  input  and output  there are  two pins  in 8085 microprocessor

Find the t-domain forced response in glc parallel circuit, Consider a GLC p...

Consider a GLC parallel circuit excited by i(t) = Ie st in the time domain. Assume no initial inductive current or capacitive voltage at t = 0. Draw the transformed network in the

Calculate critical angel and fundamental gaussian mode, (1) An argon ion la...

(1) An argon ion laser, emitting light at a wavelength of 488nm with a beam divergence of 150 firad, is used to illuminate the moon. (i) Assuming the earth-to-moon distance is 3

Find the resonant angular frequency, Consider the circuit shown in Figure w...

Consider the circuit shown in Figure with R 0 , (b) the quality factor Q, and (c) the maximum impedance Z m . Comment on the applicability of the universal resonance curve.

Find out which of the two motors, Find out which of the two motors: Tw...

Find out which of the two motors: Two three-phase induction motors while connected across a 400 V, 50 Hz supply are running at 1440 and 940 RPM respectively. Find out which of

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