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

Calculate the magnetic flux in the core, Q. A toroid with a circular cross ...

Q. A toroid with a circular cross section is shown in Figure. It is made from cast steel with a relative permeability of 2500. The magnetic flux density in the core is 1.25 Tmeasur

Determine the force applied to the plunger by system, Q. For the electromag...

Q. For the electromagnet shown in Figure, the λ-i relationship for the normalworking range is given by i = aλ 2 + bλ(x -d) 2 ,where a and b are constants. Determine the force app

Find the per-phase impedance of the load, Q. A three-phase, three-wire 208-...

Q. A three-phase, three-wire 208-V system is connected to a balanced three-phase load. The line currents ¯ IA, ¯ IB, and ¯ IC are given to be in phase with the line-to-line voltage

Water.., hot and cold lime soda process

hot and cold lime soda process

Analog-to-digital converters, Analog-to-Digital (A/D) Converters An A/D...

Analog-to-Digital (A/D) Converters An A/D converter converts analog input signals into digital output data in many areas such as process control, aircraft control, and telemetr

Find the effective noise temperature, Q. An antenna with an effective noise...

Q. An antenna with an effective noise temperature of 130 K couples through a waveguide that has a loss of 0.8 dB to a receiver. Find the effective noise temperature presented by th

Amperes circuital law, Amperes Circuital Law The    observation    tha...

Amperes Circuital Law The    observation    that    magnetic    field strength varied with distance from the wire led to the following statement: 'If  the  magnetic  field

Obtain an expression for the closed-loop transfer function, Q. A noninverti...

Q. A noninverting op-amp circuit and its closed-loop representation are given in Figure. Obtain an expression for the closed-loop transfer function H(ω) = Y (ω)/X(ω) and comment on

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