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

Power system engineering, A three-phase transposed line is composed of one ...

A three-phase transposed line is composed of one ACSR conductor per phase with flat horizontal spacing of 11 meters as shown in Figure (a). The conductors have a diameter of 3.625

Mathematics, The two sides of a triangle are 17 cm and 28 cm long, and the ...

The two sides of a triangle are 17 cm and 28 cm long, and the length of the median drawn to the third side is equal to 19.5 cm. Find the distance from an endpoint of this median to

Digital electronics, Design a recycling MOD 19 up counter using JK FFs. In ...

Design a recycling MOD 19 up counter using JK FFs. In your design, include the logic circuit diagram and the timing diagram output that counts from 000002 = 010 to 100112 = 1910. C

How to get solution in taxation assignment help, i need help with taxation ...

i need help with taxation assignment help, how do i get solution for it?

Linear components, A linear circuit component is one that has a linear I V ...

A linear circuit component is one that has a linear I V characteristic

Superposition, advantages and disadvantaages of superposition

advantages and disadvantaages of superposition

Determine the maximum value of the voltage, Q. Three waveforms seen on an o...

Q. Three waveforms seen on an oscilloscope are shown in Figure. If the horizontal scale is set to 50 ms per division (500 ms for the entire screen width), and the vertical scale is

Engineering, State the different stabilization techniques and compensation ...

State the different stabilization techniques and compensation techniques

Datapath and a datapath logic cell, Explain what is meant by a datapath and...

Explain what is meant by a datapath and a datapath logic cell illustrating your answer by reference to a suitable function using diagrams as appropriate. Show using a diagram ho

D.c.machines, can voltage regulation be negative?why?

can voltage regulation be negative?why?

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