In Class 12 Semiconductor Physics, the most fundamental and magical device you study is the PN Junction Diode. A diode is basically a 'one-way street' for electricity. It allows electric current to flow perfectly in one direction but completely blocks it from flowing backwards.
This one-way magic entirely depends on how you connect the battery to it—a concept known as Forward Bias and Reverse Bias.
Forward Bias Connection: P connected to Positive (+), N connected to Negative (-).
Reverse Bias Connection: P connected to Negative (-), N connected to Positive (+).
Current Flow: Forward Bias acts like a closed switch (Current flows). Reverse Bias acts like an open switch (Zero current).
Depletion Region: It shrinks and disappears in Forward Bias, but grows massively thick in Reverse Bias.
A diode is made of two blocks of silicon:
A diode is in Forward Bias when you connect the Positive terminal of the battery to the P-type block, and the Negative terminal to the N-type block.
A diode is in Reverse Bias if you hook the battery up backward: The Negative terminal is connected to the P-type, and the Positive terminal to the N-type.
In forward bias, the diode allows full electric current to flow through it. In reverse bias, the diode acts as a solid brick wall, completely blocking the current.
To connect it in forward bias, you must attach the P-type (Anode) to the positive terminal of the battery, and the N-type (Cathode) to the negative terminal.
In reverse bias, the depletion region expands and becomes much wider, creating a massive barrier that stops electrons from crossing.
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