Forward and reverse bias
Applying a potential difference across a p-n junction from an outside source is biasing it. It behaves differently depending on the direction.
Activity 11.1
You will need: a 1N4001 diode, a 2.5 V torch bulb, two 1.5 V dry cells, a switch and wires
- Connect the diode as in figure 1 (a project board helps) and switch on. Watch the bulb.
- Reverse only the battery, as in figure 2, and switch on again.
Figure to be added
The observation
The bulb lights only when the diode is connected as in figure 1. A diode lets current through in one direction only.
Forward bias
p side to +, n side to −.
Holes and electrons are pushed towards the junction; the depletion layer narrows.
Below the barrier (0.7 V for Si) only a negligible current flows; above it, a considerable current.
Reverse bias
p side to −, n side to +.
Electrons are pulled to the + side and holes to the − side; the depletion layer widens.
No current flows.
Figure to be added