Module 6 : PHYSICS OF SEMICONDUCTOR DEVICES
Lecture 34 : Intrinsic Semiconductors
  Example 8
Exercise 7
   
  A compensated semiconductor contains both donor and acceptor impurities. The compensation is said to be complete if $ N_d=N_a$ in which case the semiconductor behaves like an intrinsic semiconductor.
  Example 9
  Condition of Charge Neutrality
  In the absence of an electric field, a bulk material is charge neutral. Let
  $ n=$ number density of electrons
  $ p=$ number density of holes
  For an intrinsic semiconductor $ n=p=n_i$ so that the number density of electrons may be written as
 
$\displaystyle n_i = \sqrt{np}$
  Let the density of donor atoms be denoted by $ N_d$ and that of acceptor atoms by $ N_a$. If the corresponding densities of ionized donors and acceptors are $ N_d^+$ and $ N_a^-$ respectively, the charge neutrality condition for the bulk sample becomes
   
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