Tubes, Discrete Solid State Devices, and Integrated Circuits 319denote a mobile particle that has a positive charge and
that simulates the properties of an electron having a
positive charge.
When a germanium crystal containing holes is
subjected to an electrical field, electrons jump into the
holes, and the holes appear to move toward the negative
terminal of the external voltage source.
When a hole arrives at the negative terminal, an elec-
tron is emitted by the terminal, and the hole is canceled.
Simultaneously, an electron from one of the covalent
bonds flows into the positive terminal of the voltage
source. This new hole moves toward the negative
terminal causing a continuous flow of holes in the crystal.
Germanium crystals having a deficiency of elec-
trons are classified p-type germanium. Insofar as the
external electrical circuits are concerned, there is no
difference between electron and hole current flow.
However, the method of connection to the two types of
transistors differs.
When a germanium crystal is doped so that it
abruptly changes from an n-type to a p-type, and a posi-
tive potential is applied to the p-region, and a negative
potential is applied to the n-region, the holes move
through the junction to the right and the electrons move
to the left, resulting in the voltage-current characteristic
shown in Fig. 12-10A. If the potential is reversed, both
electrons and holes move away from the junction until
the electrical field produced by their displacement coun-
teracts the applied electrical field. Under these condi-
tions, zero current flows in the external circuit. Any
minute amount of current that might flow is caused by
thermal-generated hole pairs. Fig. 12-10B is a plot of
the voltage versus current for the reversed condition.
The leakage current is essentially independent of the
applied potential up to the point where the junction
breaks down.Figure 12-9. Atomic structure of germanium.
+4 +4+4 +4+4+4 +4+5 +5+4+4 +4 +4+4 +4+3+4 +4+4+3+4ElectronFree
electronFree
electronGermanium
nucleusCovalent
bondHoleHole++A. Atomic structure of a pure germanium crystal.
In this condition germanium is a poor conductor.B. Atomic structure of an n-type germanium
crystal when a doping agent containing
five electrons is induced.C. Atomic structure of a p-type germanium crystal
when a doping agent containing
three electrons is induced.Figure 12-10. Voltage-versus-current characteristics.1010.1IBreakdownVI – MAA. Voltage-versus-current characteristic of the junction.B. Voltage-versus-current characteristic of
the junction transistor with the battery
polarities in the reverse condition.V