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

Electricity hazards in the laboratory, ELECTRICITY HAZARDS IN THE LABOR...

ELECTRICITY HAZARDS IN THE LABORATORY : You've probably read about, or heard of, people falling onto high voltage rails or cables and surviving thousands of volts. As a contra

Digital demodulator processes, Q. Digital demodulator processes? The fu...

Q. Digital demodulator processes? The functions of the receiver in Figure are the inverse of those in the transmitter. At the receiving end of a digital communication system, t

Explain two types of materials that are formed after doping, Explain the tw...

Explain the two types of materials that are formed after doping. Depending on the impurity added, extrinsic semiconductors can be then subdivided in two types of class: N-ty

Requirement specification for the monitor and alarm system, Prepare a User ...

Prepare a User Requirement Specification for the monitor and alarm system. User Requirements Specification should be written in a clear and unambiguous manner to state: • The

Determine the stations visual-carrier frequency, If a television station op...

If a television station operates on UHF channel 20 (band 506-512 MHz), determine the station's visual-carrier frequency.

Sketch the timing diagram for a 4-bit ripple counter, Q. Sketch the timing ...

Q. Sketch the timing diagram for a 4-bit ripple counter which uses T flip-flops.

Analysis in equilibrium, Analysis in equilibrium : Solution of Poisson'...

Analysis in equilibrium : Solution of Poisson's Equation with suitable boundary conditions - Non-equilibrium analysis: The electron and hole densities are no longe

Wireless cellular systems, i want help in builiding a simulator of cellular...

i want help in builiding a simulator of cellular systems under different frequency reuse scenarios?

Difference between the shifts and rotate instructions, What is the differen...

What is the difference between the shifts and rotate instructions? A rotate instruction is a closed loop instruction. That is, the data moved out at single end is put back in 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