Intrinsic Semiconductors
An atom is composed of a nucleus, which contains positively charged protons and
neutral neutrons, and negatively charged electrons that, in the classical sense, orbit
the nucleus. The electrons are distributed in various “shells” at different distances
from the nucleus, and electron energy increases as shell radius increases. Electrons
in the outermost shell are called valence electrons, and the chemical activity of a
material is determined primarily by the number of such electrons.