Module 6 : PHYSICS OF SEMICONDUCTOR DEVICES
Lecture 33 : Mobility of Electrons and Holes
Mobility of Electrons and Holes
When an electric field $ {\cal E}$ is applied to a metal or a semiconductor, the carriers are accelerated; the equation of motion being given by Newton's law
 
$\displaystyle \frac{d^2x}{dt^2} = \frac{q{\cal E}}{m}$
  Since the carriers continuously collide with atoms, the above equation is valid only during the time between two successive collisions. The change in velocity between two successive collisions with an interval $ t$ is given by
 
$\displaystyle \Delta v = \frac{q{\cal E}}{m}t$
  In the absence of a field the carriers exhibit random motion due to chaotic changes in their thermal velocities so that the average change in velocity over a long period of time is zero.
   
 
\includegraphics{fig5.10.eps}
 
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