What is a PN Junction Diode?
A PN junction diode is the most basic semiconductor device made of
- P-type materials and
- N-type materials.
It only enables current to flow in one way which makes it the electrical barrier.
V-I characteristics of a PN diode (Germanium-Ge)
Forward Bias
When the diode’s positive terminal is connected to positive power supply, electricity can flow.
Germanium diodes have a knee voltage of approximately 0.3 V.
Reverse Bias
When polarity is reversed, no current should flow (save for a small leakage current).
At some time, Reverse Breakdown Voltage (VRB) develops causing a significant increase in current.
Key Parameters
Knee Voltage (Vb): 0.3 V for Ge (0.7 V for Si)
Reverse Saturation Current (Is): Minimal leakage during reverse bias.
Thermal Voltage (VT): 26 mV at 300 K
Reverse Breakdown Voltage (VRB): Sudden current increase in reverse.
Equation
Why Does It Matter?
Basis of rectifiers (AC-DC conversion)
Protects circuits from the reverse polarity.
Utilized in signal processing, switching & logic circuits.
Foundation for LEDs, Solar cells, Zener diodes and more.
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