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

Electromagnet.., force and torque in magnetic field system

force and torque in magnetic field system

What is effect of overheating on an electric insulator, What is the effect ...

What is the effect of overheating on the life of an electric insulator? An insulator is designed to withstand amount of heat. However, when an insulator is overheated so dielec

Lead acid accumulators with electrical equipment, Lead Acid Accumulators : ...

Lead Acid Accumulators : These are the most common storage batteries which can deliver a heavy current when short-circuited. There are also many other hazards with these accumulat

Microprocessor, highest priority interrupt in 8085 microprocessor

highest priority interrupt in 8085 microprocessor

Binary multiplication, Q. What do you mean by Binary Multiplication? Th...

Q. What do you mean by Binary Multiplication? The Rules of Binary Multiplication 0 x 0 = 0 0 x 1 = 0 1 x 0 = 0 1 x 1 = 1 , and no carry or borrow

Determine line voltage for the y- connected machine, A 3-phase, 16-pole syn...

A 3-phase, 16-pole synchronous machine is driven by a prime mover at a speed of 600-rpm with the stator open circuited. The rotor flux per pole is 0.025-Wb. Determine (a) the fr

Physical operation of the junction of diode, Q. Physical operation of the j...

Q. Physical operation of the junction of diode? The physical operation of the junction can be described in terms of the charge-flow processes. Usually there is a greater concen

Discuss the nature of sinusoidal signal, Q. Discuss the nature of sinusoida...

Q. Discuss the nature of sinusoidal signal? Discuss the nature of evenness and oddness of: (a) The sinusoidal signal x(t) = A cos(2πf 0 t + θ). (b) The complex exponentia

Calculate the reflection of wedge, The corners of wedge-shaped block are A(...

The corners of wedge-shaped block are A(0,0,2), B(0,0,3), C(0,2,3), D(0,2,2), E(-1,2,2) and F(-1,2,3) and the reflection plane goes the Y-axis at 450 between (-X) & (Z) axis. Calcu

What is photovoltaics?, Photovoltaics  is a high-technology approach  to ch...

Photovoltaics  is a high-technology approach  to changing sunlight  directly  into  electrical  energy.  The  electricity  is direct  current  and  can  be  used  that  way,  chnag

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