Module 6 : PHYSICS OF SEMICONDUCTOR DEVICES
Lecture 35 : Photoconductivity
 
 
   
  Consider an n-type semiconductor. If the recombination life time for the minority carriers is $ \tau_p$, the rate of change of carrier concentration is given by
 
$\displaystyle \frac{d}{dt}(\Delta p) = \frac{\eta\alpha I}{h\nu}-\frac{\Delta p}{\tau_p}$
  Under steady state condition $ d\delta p/dt=0$, which gives
 
$\displaystyle \delta p = \frac{\eta\alpha I_p\tau_p}{h\nu}= \Delta n$
  This excess hole density leads to an additional conductivity
 
$\displaystyle \Delta\sigma = q\delta n\mu_e + q\Delta p \mu_h$
 
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