Semiconductor Fundamentals · Topic 10 of 13
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Diode
A single p–n junction packaged as a one-way current valve.
What you’ll learn
- How a diode uses the p–n junction
- The I–V characteristic
- Common diode types
Why it matters
Diodes rectify, protect, and emit light — and the diode I–V law recurs throughout electronics.
Explanation
A diode is a p–n junction with two terminals: the anode (p) and cathode (n). It conducts when forward-biased beyond its turn-on voltage and blocks when reverse-biased, up to a breakdown voltage.
The current rises exponentially with forward voltage, described by the Shockley diode equation.
Visual explanation
Key terminology
- Anode / cathode
- The p-side and n-side terminals.
- Turn-on voltage
- Forward voltage where the diode begins to conduct (~0.7 V for silicon).
- Breakdown
- Reverse voltage at which the diode suddenly conducts.
Formula
Shockley diode equation; Vt = kT/q ≈ 26 mV at room temperature.
Example
Common mistakes
Watch out for:
- Treating the turn-on voltage as fixed — it varies with current and temperature.
- Ignoring reverse breakdown, which is intentional in Zener diodes.
Real-world application
LEDs are diodes engineered to emit light; photodiodes do the reverse.
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Diode
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MOSFET
Semiconductor Fundamentals
The voltage-controlled switch that makes up modern logic.
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