Video Transcript
The diagram shows a PN junction in
a circuit. The positively charged side of the
junction’s depletion region is shown in red, and the negatively charged side is
shown in blue. Is the junction forward biased or
reverse biased?
The question asks us to determine
whether, in the diagram, the PN junction is forward biased or reverse biased. First, let’s remember some
important aspects of a PN junction connected to a power supply in an electrical
circuit.
There are two possible ways to
connect the junction to a power supply: forward biased, where the positive terminal
of the power supply is connected to the P-type side, while the negative terminal is
connected to the N-type side, or reverse biased, where the negative terminal of the
power supply is connected to the P-type side and the positive terminal is connected
to the N-type side.
Looking at our diagram, we can see
that there is a net positive charge on the left-hand side of the depletion region
and a net negative charge on the right-hand side of the depletion region. The side of the junction that has
net positive charge around the depletion region is the N-type side. The side of the junction that has
net negative charge around the depletion region is the P-type side.
We can see then that the positive
terminal of the power supply connects to the N-type side of the junction. And the negative terminal of the
power supply connects to the P-type side of the junction. The junction is therefore reverse
biased.
