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

High pressure gas hazards, High Pressure Gas Hazards When we consider t...

High Pressure Gas Hazards When we consider the dangers of compressed gas in the lab, there are three main sources of danger as follows: 1) Sudden release of high pressure ga

Explain significance of loss tangent of dielectric material, Explain the si...

Explain the significance of the loss tangent of a dielectric material. The loss tangent contains a very small value for free space. For solid materials there tan δ = 0.003, tha

Role of consumers in distribution reform, Role of Consumers in Distribution...

Role of Consumers in Distribution Reform In the reforms procedure, mandatory metering for all consumers is being implemented.  Consumers should implement this measure. Public

What is the function of dma address register, What is the function of DMA a...

What is the function of DMA address register? Every DMA channel has one DMA address register. The function of this register is to keep the address of the starting memory locati

What is frequency translation and product modulation, Q. What is Frequency ...

Q. What is Frequency Translation and Product Modulation? The basic operation needed to build modulators is the multiplication of two signals. Whenever sinusoids are multiplied,

Digital electronics, Design a recycling MOD 19 up counter using JK FFs. In ...

Design a recycling MOD 19 up counter using JK FFs. In your design, include the logic circuit diagram and the timing diagram output that counts from 000002 = 010 to 100112 = 1910. C

Name the elements related to capacitance, Elements related to capacitance ...

Elements related to capacitance a.  Electric field: Area that surrounds the electric charge or charges system where the enhancing and reducing of electric force exists.

What is ringer circuit in telephone hand set, Q. What is Ringer Circuit in ...

Q. What is Ringer Circuit in telephone hand set? Purpose of the ringer is to alert destination party of incoming calls. Audible tone from the ringer should be load enough to be

Wiring a plug , Wiring a Plug : Let us consider the problem of connect...

Wiring a Plug : Let us consider the problem of connecting a 16 A plug, commonly known as 15 A or power plug to an electrical appliance. Do you use any old bit of wire, or any

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