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

Superposition theroem, what are the limitations of superposition theroem

what are the limitations of superposition theroem

Three phase induction motors - motor control , Three Phase Induction Motors...

Three Phase Induction Motors A three  phase induction rotor  consists  a stators  and a motor stator has balanced three  phase  winding. These windings  are distributed in the

Transformers, AC Operation of an iron core         ...

AC Operation of an iron core         Hence, if a wattmeter were used to measure the power delivered over a full period of the waveform (which will also b

Assignment question , An audio amplifier with feedback needs gain of approx...

An audio amplifier with feedback needs gain of approximately 500 in a 3-dB bandwidth extending from 60 Hz to 25 kHz. Assume this is accomplished using a feedback network with ß=0.0

Describe schmitt trigger, a) Describe Schmitt trigger with the help of tran...

a) Describe Schmitt trigger with the help of transfer characteristics. b) Also get the expression of hysteresis voltage VH and output waveform for sinusoidal input signal

Determine the largest crest factor, A quantizer has 130 quantum levels that...

A quantizer has 130 quantum levels that exactly span the extremes of a symmetrically ?uctuating message with step size δv = 0.04 V. Determine the following: (a) |f(t)|max.

Analog communication systems, Q. Analog communication systems? An analo...

Q. Analog communication systems? An analog message is a continuum of possible amplitudes at any given time, and analog signals are continuous in time and in amplitude, such as

Show twos complement addition, Q. Can you explain Twos complement addition?...

Q. Can you explain Twos complement addition? 2's Complement Addition Two's complement addition follows the same rules as binary addition. For example, 5 + (-3)  =  2

Single-axis autopilot control system of an aircraft, Q. Single-axis autopil...

Q. Single-axis autopilot control system of an aircraft? Figure (a) shows the block diagram of a simplified single-axis (pitch, yaw, or roll) autopilot control systemwith digita

Explain about subscriber loop system, Q. Explain about Subscriber Loop Syst...

Q. Explain about Subscriber Loop System? Subscriber Loop System:Each subscriber in a telephone network is connected normally to the nearest switching office by a dedicated pair

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