Electrons and holes, Electrical Engineering

Assignment Help:

Electrons and Holes

  • For T> 0 K, there would be some electrons in the otherwise empty conduction band, and some empty states in the otherwise filled valence band.
  • The empty states in the valence band are referred to as holes.
  • If the conduction band electron and the valence band hole are created by thermal excitation of a valence band electron to the conduction band, then they are called electron-hole pair (EHP).
  • After excitation to the conduction band, an electron is surrounded via a large number of empty states, for example the equilibrium number of EHPs at 300 K in Si is ∼1010/cm3, whereas the Si atom density is ∼1022/cm3 .
  • Thus, the electrons in the conduction band are free to move about via the many available empty states.
  • Corresponding problem of charge transport in the valence band is slightly more complex.
  • Current transport in the valence band can be accounted for by keeping track of the holes themselves.
  • In a filled band, all available energy states are occupied.
  • For every electron moving with a given velocity, there is an equal and opposite electron motion somewhere else in the band.
  • Under an applied electric field, the net current is zero, since for every electron j moving with a velocity Vj , there is a corresponding electron j moving with a velocity - Vj .
  • In a unit volume, the current density J can be given by

1147_Electrons and Holes 1.png (filled band)   (2)

  • where N is the number of electrons/cm3 in the band, and q is the electronic charge.
  • Now, if the jth electron is removed and a hole is created in the valence band, after that the net current density

1055_Electrons and Holes 2.png

  • Thus, the current contribution of the empty state (hole), obtained by removing the jth electron, is equivalent to that of a positively charged particle with velocity Vj.
  • Note that actually this transport is accounted for by the motion of the uncompensated electron j having a charge of q and moving with a velocity Vj.
  • Its current contribution (-q) (-Vj) is equivalent to that of a positively charged particle with velocity + Vj.
  • For simplicity, therefore, the empty states in the valence band are called holes, and they are assigned positive charge and positive mass.
  • The electron energy increases as one move up the conduction band, and electrons gravitate downward towards the bottom of the conduction band.
  • On the other hand, hole energy increases as one moves down the valence band (since holes have positive charges), and holes gravitate upwards towards the top of the valence band.

Related Discussions:- Electrons and holes

Working principle of ultrasonic machining, Explain the basic working princi...

Explain the basic working principle of ultrasonic machining with the help of diagram. What are the different kinds of tool materials explain, tool holders are used in ultrasonic

Communication, can I get matlab code for out of band radiation reduction of...

can I get matlab code for out of band radiation reduction ofdm system

Calculate the saturation current of the diode, Q. A silicon diode is forwar...

Q. A silicon diode is forward-biased with V = 0.5 V at a temperature of 293 K. If the diode current is 10 mA, calculate the saturation current of the diode.

Calculate the magnetic flux in the core, Q. A toroid with a circular cross ...

Q. A toroid with a circular cross section is shown in Figure. It is made from cast steel with a relative permeability of 2500. The magnetic flux density in the core is 1.25 Tmeasur

Scale-space pyramids, Scale-space pyramids   Write an m-file "scale_s...

Scale-space pyramids   Write an m-file "scale_space.m" which computes scale space representation of an input image for a given scale "sigma" and displays them. (i) 4 scale

Consequent effects on the real and reactive power losses, Q. Consider an up...

Q. Consider an upgrade of a three-phase transmission system in which the operating line-to-line voltage is doubled, and the phase or line currents are reduced to one-half the previ

Dc motor, write the working and construction of dc motor.

write the working and construction of dc motor.

System of forces.., Example of unlike coplaner parallel force''

Example of unlike coplaner parallel force''

Inverting integrator circuit, Q. Consider the inverting integrator circuit ...

Q. Consider the inverting integrator circuit shown in Figure. Let C = 0.4µF and R = 0.1M. Sketch v o for a period of 0.5 s after the application of a constant input of 2 V at the

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