covalent bonding yields seven electrons in the outer
shell. This leaves an opening for another electron and
is shown in figure 1-6. This space is called a hole and
can be considered a positive charge, just as the extra
electrons that exist in N-type semiconductor material
are considered a negative charge. Materials that have
holes in their outermost electron shells are called
positive or P-type materials. To understand the
behavior of P-type semiconductors, it is necessary to
look upon the hole as a positive current carrier, just as
the free electron in N-type semiconductors are
considered negative current carriers. Just as electrons
move through N-type semiconductors, holes move
from atom to atom in P-type semiconductors.
Movement of holes through P-type semiconductors,
however, is from the positive terminal to the negative
terminal. For this reason, any circuit analysis of solid-
state circuitry is done on the basis of positive to
negative (conventional) current flow.
When a source voltage, such as a battery, is
connected to N-type material, an electric current will
flow through it, as shown in figure 1-7. The current flow
in the N-type semiconductor consists of the movement
of free electrons, the same as the current flow through a
natural conductor, such as copper. When a current
source of sufficient voltage is connected across a P-type
material, an electric current will also flowthrough it, but
any current flow in a P-type semiconductor is looked
upon as the movement of positively charged holes. The
holes appear to move toward the negative terminal, as
the electrons enter the material at the negative terminal,
fill the holes, and then move from hole to hole toward
the positive terminal. As is the case with the N-type
semiconductors, the movement of electrons through
P-type semiconductors toward the positive terminal is
motivated by the natural attraction of unlike charges.
Figure 1-6.Boron-doped silicone.
Figure 1-7.Hole movement theory.