ELECTRONIC PRINCIPLES 0D1647 LESSON 1/TASK 2
valence electrons between two or more atom . It is this bonding
that holds the atoms together in an orderly structure called a
CRYSTAL, (figure 73).
semiconductor is accomplished by two different types of current
flow: HOLE FLOW and ELECTRON FLOW. Hole flow is very similar to
electron flow except that holes (positive charges) move toward a
negative potential and in an opposite direction to that of the
electrons. In an INTRINSIC semiconductor (one which does not
contain any impurities), the number of holes always equals the
number of conducting electrons (figure 74 on the following page).
of selected additives, called impurities, are added to
semiconductors to increase their current flow. Semiconductors
which undergo this treatment are referred to as EXTRINSIC
SEMICONDUCTORS (figure 75 on the following page).
FIGURE 73. TYPICAL CRYSTAL STRUCTURE.