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

What is the physical length of this cable, Q. It is desired to cut a λ/4 le...

Q. It is desired to cut a λ/4 length of RG58A/U cable (ε r = 2.3) at 150MHz.What is the physical length of this cable?

#kinetic energy, how does the increase in the kinetic energy of a proton co...

how does the increase in the kinetic energy of a proton compare with the increase in kinetic energy of the alpha particle in part?

Determine the value of voltage using offset diode model, Use the offset dio...

Use the offset diode model with a threshold voltage of 0.6 V to determine the value of v 1 for which the diode D will first conduct in the circuit of Figure(a).

Allocative efficiency, Allocative Efficiency: A neoclassical concept refer...

Allocative Efficiency: A neoclassical concept referring to allocation of productive resources (labour, capital, etc.) in a manner that best maximizes well-being (or 'utility') of

Power system, a rectangular surge of 2us duration and magnitude of 100Kv tr...

a rectangular surge of 2us duration and magnitude of 100Kv travels along a line of surge impedance 500 ohms. The latter is connected to another line of equal impedance through an i

What are the modes used in display modes, What are the modes used in displa...

What are the modes used in display modes? 1. Left Entry mode In the left entry mode, the data is going into from the left side of the display unit. 2. Right Entry Mode

Electrical machine, Design a suitable double –layer lap winding for a 6-pol...

Design a suitable double –layer lap winding for a 6-pole dc armature with 18 slots and two coil sides per slot. Give values of front-pitch, brack–pitch and commutator pitch. Draw t

Armature reaction, is armature reaction good or bad for dc generator?

is armature reaction good or bad for dc generator?

Shld store hl pair direct instruction , SHLD Store HL pair Direct Instructi...

SHLD Store HL pair Direct Instruction This  instruction is used to store the contents of HL  register  pair to  memory  address specified  in the  instruction and the  next ad

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