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

Convolution, Convolution :   (i) Express this function in terms of kern...

Convolution :   (i) Express this function in terms of kernel coefficients and convolve with image class.png, (x,y are coordinates of pixels) Io(x,y)=I(x+1,y)-2*I(x,y)+I(x-1,

Instrumentation, explain measurement of frqueny and phase using cro

explain measurement of frqueny and phase using cro

Power distribution, Power Distribution You will study about the legisl...

Power Distribution You will study about the legislative measures that have been taken by our government to address these challenges. In particular, we discuss the Energy Conse

Determine the Service and Backwash Rates, Determine the Service and Backwas...

Determine the Service and Backwash Rates The system on site is a pressure sand filter, with a service curve. The filter is backwashed using the feed pump, at a higher flow rate, s

Define the property under which resistance of metals vanish, The property d...

The property due to which the resistance of some metal or compound vanishes under certain conditions is (A) Semi conductivity.                     (B) Super conductivity.

Magnetic field in the core, We can use Ampere's Law to calculate the magnet...

We can use Ampere's Law to calculate the magnetic field in the core.

When input is a triangular wave, Q. When input is a triangular wave. W...

Q. When input is a triangular wave. When the input fed to differentiating circuit is a triangular wave, the output will be a rectangular wave. During the period OA of

Show basic construction of mosfet, Q. Show Basic Construction of MOSFET? ...

Q. Show Basic Construction of MOSFET? The basic construction of the n-channel depletion-type MOSFET is provided in Figure. A slab of p-type material is formed from a silicon

Electronic and electrical measurement CRO., Describe the construction and w...

Describe the construction and working of atleast two types of storage CRO

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