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

Explain the working principle of an opto coupler, Q. Explain the working pr...

Q. Explain the working principle of an opto coupler? When it is necessary to block the voltage between one electronic circuit and another, and transfer the signal at the same t

Determine the admittance of the parallel combination, Q. The voltage across...

Q. The voltage across a parallel combination of a 100- resistor and a 0.1-µF capacitor is 10 cos(5000t +30°) V. Determine the admittance of the parallel combination and find the c

What is elementary diode circuits, Q. What is Elementary Diode Circuits? ...

Q. What is Elementary Diode Circuits? Semiconductor diodes are used in a wide variety of applications. Their usage abounds in communication systems (limiters, gates, clippers,

OUT Output Instruction , OUT Output Instruction This instruction is us...

OUT Output Instruction This instruction is used  send data byte  stored in the accumulator  to the  output  port  whose  address  specified in the instruction. The instruction

Draw and explain the r-2r ladder dac, Question 01 Convert the following bi...

Question 01 Convert the following binary numbers to its specified number system 111.101 (2) to octal 10111 (2) to decimal 0.1010 (2) to hexadecimal 1011.11 (2)

Forward bias, Forward bias In forward bias, the p-type is linked with...

Forward bias In forward bias, the p-type is linked with the positive terminal and the n-type is linked with the negative terminal.In forward bias mode the PN junction operati

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