Figure 81. PN Junction Barrier Formation

Electronic Principles
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(3) Junction Barrier. A junction barrier is an electrostatic

field which has been created by joining a section of N material

with a section of P material. Since holes and electrons must

overcome this field to cross the junction, the electrostatic

field is commonly called a BARRIER. Because there is a lack or

depletion of free electrons and holes in the area around the

barrier, this area has become known as the DEPLETION REGION

(figure 81).

FIGURE 81. PN JUNCTION BARRIER FORMATION.

(a) Forward Bias. Forward bias is an external voltage which

is applied to a PN junction to reduce its barrier and,

therefore, aid current flow through the junction. To accomplish

this function, the external voltage is connected so that it

opposes the electrostatic field of the junction (figure 82 on

the following page).

(b) Reverse Bias. Reverse bias is an external voltage which

is connected across a PN junction so that its voltage aids the

junction, thereby offering a high resistance to current flow

through the junction (figure 83 on the following page).

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