Mobility verus impurity concentration graph

Discussion in 'Homework Help' started by hitmen, Dec 28, 2009.

  1. hitmen

    Thread Starter Active Member

    Sep 21, 2008
    For semiconductors there is a graph of mobility in cm2/Vs plotted against total impurity concentration Nt in atoms/cm3

    My question is why the impurity doping is expressed as total hole concentration and electron concentration added together.

    Wouldnt the 'holes' and 'electrons' cancel each other out in a semiconductor?
  2. Papabravo


    Feb 24, 2006
    There are two types of impurities. Type III(p-type) and Type V(n-type) based on the column from the periodic table. These are also called by the names acceptor and donor. Some doping is done when the boule is grown and the remaining dopants are added by diffusion or ion-implantation. You must take into account both the majority carriers of the dopant with the higher concentration as well as the minority carriers from the dopant with the lower concentration.