General Science

  • noun a foreign substance present at a low concentration in a another substance


  • A substance whose presence within another reduces or eliminates the purity of the latter. The presence of an impurity in a crystal can change its properties significantly, as seen in the use of dopants in semiconductors, or in the photoconductivity of an allochromatic crystal.
  • An impurity (1) which is introduced into a semiconductor material. Such an impurity may be an acceptor impurity, which makes for a p-type semiconductor, or it may be a donor impurity, which makes for an n-type semiconductor. Acceptor impurities include gallium and aluminum, while donor impurities include phosphorus and arsenic. In either case, such an impurity increases the conductivity of the semiconductor. Also called dopant, or semiconductor dopant.


  • noun a substance that is not pure or clean