Chapter 2: Semiconductor Fundamentals Solid materials are
classified by the way the atoms are arranged within the solid.
Materials in which atoms are placed at random are called
amorphous. Materials in which atoms are placed in a highly
ordered structure are called crystalline. Poly-crystalline
materials are materials with a high degree of short-range order
and no long-range order. These materials consist of small
crystalline regions with random orientation called grains,
separated by grain boundaries. Crystals naturally form as liquid
material cools down, since the close proximity of atoms lowers
their energy. However, since crystallization typically occurs in
multiple locations simultaneously, one finds that the poly-
crystalline structure is quite common except for materials such
as glass which tend to be amorphous. Crystalline silicon dioxide
does occur in the form of quartz but only if the temperature and
pressure promote crystal formation. Of primary interest in this
text are crystalline semiconductors i