Module 6 : PHYSICS OF SEMICONDUCTOR DEVICES
Lecture 34 : Intrinsic Semiconductors
   
Exercise 2
  Exercise 3
 
  Current in an intrinsic semiconductor
  For semiconductors both electrons and holes contribute to electric current. Because of their opposite charge, their contribution to the current add up. For an intrinsic semiconductor with a single valence band and a conduction band, the current density is given by
 
$\displaystyle J = q(nv_e+ pv_h)$
  where $ n$ and $ v_e$ are respectively the electron density and speed while $ p$ and $ v_h$ are the hole density and speed. Using $ v_e=\mu_e {\cal E}$ and $ v_h = \mu_h{\cal E}$ and the fact that $ n=p=n_i$, we have
 
$\displaystyle J = q{\cal E}n_i(\mu_e+\mu_h)$
  which gives the conductivity as
 
$\displaystyle \sigma = qn_i(\mu_e+\mu_h)$
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