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

Wye-delta transformation., what is the literature review about wye delta tr...

what is the literature review about wye delta transformation?? for 3 paragraphs atleast*

Evaluate the transfer function of the nested-loop system, Q. Determine the ...

Q. Determine the transfer function C(s)/R(s) of the nested-loop feedback system shown in Figure.

Disaster management, role of electrical engineer in disaster management

role of electrical engineer in disaster management

Energy band diagram, E n e r gy Band Diagram Energy band d...

E n e r gy Band Diagram Energy band diagram in qualitative form is sketched by following the following process: 1. The semiconductor device is supposed to be ma

Calculate the sending end voltage, A 150 km long, 3-phase, 400 kV overhead ...

A 150 km long, 3-phase, 400 kV overhead line is used to transmit 1800 MW to a distribution area at 0.9 power factor lagging. The line parameters per phase and per unit length in st

True / false , filt is a circuit that cantains onely passive components

filt is a circuit that cantains onely passive components

What is the purpose of clock signal in an 8086 system, What is the purpose ...

What is the purpose of clock signal in an 8086 system? 8086 needs clock signal with 33%duty cycle from some external operations.8086 processor needs 5 MHZ clock signal

Resultant force, State and prove parallelogram law of forces and explain i...

State and prove parallelogram law of forces and explain it''s applications

Battery service provider system specification, The vehicle batteries shall ...

The vehicle batteries shall be owned by the battery service provider. The automobile battery shall be recyclable, environmentally friendly, and safe. The battery service pr

Dc motor, write the working and construction of dc motor.

write the working and construction of dc motor.

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