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

Determine l and c of the band reject filter circuit, Q. Determine L and C o...

Q. Determine L and C of the band reject filter circuit of Figure to have a center frequency of 100 kHz and a bandwidth of 5 kHz. Also find the Q of the filter.

assembly language program , Write an Assembly language program that will p...

Write an Assembly language program that will produce a PWM signal with a desired average voltage. The user selects the desired average voltage by pressing keys 1 - 4. If the

Dc machines, compound generator drawback

compound generator drawback

Assignment, Hi, I got assignment to design a power electronic system Design...

Hi, I got assignment to design a power electronic system Design the circuit and select the appropriate components for that circuit to fulfil the requirements of the device. Regards

Voltage divider with ac bypasses capacitor, Voltage divider with AC bypasse...

Voltage divider with AC bypasses capacitor: Figure: Voltage divider with capacitor The standard voltage divider circuit that is discussed above faces a drawback - A

State kirchoff''s current law, State Kirchoff's Current Law Kirchoff's...

State Kirchoff's Current Law Kirchoff's Current Law (KCL) describes at any junction in an electric circuit the total current flowing towards that junction is equivalent to th

Effect of temperature on resistivity of conducting materials, Explain the e...

Explain the effect of temperature on the resistivity of conducting materials. The resistance of most metals rises with rise of temperature whereas that of semiconductors and el

Decimal to binary coded decimal conversions, Decimal to Binary Coded Decima...

Decimal to Binary Coded Decimal Conversions Step1. Separate the digits in the decimal number Step2. Express each of the digits in their binary equivalent Step3. Combine all o

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