Extrinsic material, Electrical Engineering

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.

Posted Date: 1/11/2013 4:44:09 AM | Location : United States







Related Discussions:- Extrinsic material, Assignment Help, Ask Question on Extrinsic material, Get Answer, Expert's Help, Extrinsic material Discussions

Write discussion on Extrinsic material
Your posts are moderated
Related Questions
Central Energy Conservation Fund This fund is to be set up at the Centre to develop the delivery mechanism for large-scale adoption of energy efficiency services like as perfo


LHLD  Load  HL Pair Direct  Instruction This  instruction is used to copy the  content  of memory  location specified  by opened  in register L  and copy the content of next  m

Q. Split-phase or resistance-split-phasemotor? Split-phase or resistance-split-phasemotors: Split-phasemotors have two statorwindings (amainwinding and an auxiliarywinding)with

Q. Explain about Transistor Amplifiers? Amplifiers are circuits that produce an output signal which is larger than, but proportional to, an input signal. The input and output s

define the physical significance of damping coefficient

electrical designer salary above 6years experience, in singapore

Illustrate the types of classification and coding systems? Briefly explain Production Flow Analysis? Discuss the basic concept of Composite part and different kinds of cell desi

PLS WRITE THE INTRODUCTION, METHODOLOGY AND LITERATURE REVIEW

i dont understand why equalizer connection is not used in wave windings?