Semiconductor Diodes - 1.3

Key Concepts

• Unidirectional Conductivity: The primary function of a diode (one-way valve).

• P-N Junction Formation: Understanding diffusion, recombination, depletion region, and built-in potential.

• Forward vs. Reverse Bias: How external voltage affects the depletion region and current flow.

• Knee Voltage (0.7V for Si): The critical voltage for forward conduction.

• Reverse Breakdown: The phenomenon of sudden reverse conduction.

• Exponential Relationship: The core of the Shockley Diode Equation.

• Thermal Voltage: Its dependence on temperature and role in the Shockley equation.

• Diode Approximations: Knowing when to use ideal, practical, or piecewise linear models for simplification.

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• Examples

• Half-Wave Rectifier: A single diode used to convert AC to pulsating DC by blocking one half-cycle of the AC waveform.

• LED Lighting: A Light Emitting Diode (LED) is a special type of diode that emits light when forward-biased.

• Reverse Polarity Protection: Diodes are often placed in series with power inputs to prevent damage to circuits if the power supply is connected with the wrong polarity.

• Voltage Regulation (Zener Diode): A Zener diode is designed to operate in the reverse breakdown region to maintain a constant voltage across its terminals, even if the current through it varies.

• Signal Clipping/Clamping: Diodes can be used to limit voltage levels (clippers) or shift DC levels (clampers) in signal processing.

• Solar Cells (Photodiodes): Photodiodes convert light energy into electrical current, forming the basis of solar panels.

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• Flashcards

• Term: Diode

• Definition: A two-terminal semiconductor device that allows current flow primarily in one direction.

• Term: P-N Junction

• Definition: The interface between p-type and n-type semiconductor materials where diode action occurs.

• Term: Depletion Region

• Definition: An area near the p-n junction depleted of free charge carriers, acting as an insulator.

• Term: Forward Bias

• Definition: Anode positive relative to cathode; diode conducts current exponentially after $V\_0$.

• Term: Reverse Bias

• Definition: Cathode positive relative to anode; diode blocks current, allowing only $I\_S$.

• Term: Knee Voltage (for Si)

• Definition: Approximately $0.7 \text{ V}$, the forward voltage at which a silicon diode starts to conduct significantly.

• Term: Reverse Breakdown Voltage

• Definition: The reverse voltage at which a diode suddenly conducts heavily in the reverse direction.

• Term: Shockley Diode Equation

• Definition: $I\_D = I\_S \left( e^{\frac{V\_D}{\eta V\_T}} - 1 \right)$, describes the diode's I-V relationship.

• Term: Ideal Diode Model

• Definition: Diode acts as a perfect short circuit in forward bias, open circuit in reverse bias.

• Term: Practical Diode Model

• Definition: Diode acts as a $V\_0$ battery in series with a short circuit in forward bias, open circuit in reverse bias.

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• Memory Aids

• "Arrow Points to No-Go for Electrons": The arrow in the diode symbol points in the direction of conventional current flow, but against the direction of electron flow.

• "P-N = Positive-Negative (charge carriers)": Helps remember the types of doping.

• "Forward, Fire\! Reverse, Resist\!": In forward bias, current fires (flows easily); in reverse bias, it resists (blocks).

• "Silicon 0.7, Germanium 0.3": Remember the approximate knee voltages.

• "Shockley's Shocking Exponential": The Shockley equation describes the diode's surprising exponential behavior.

• "Ideal is Perfect, Practical is Pretty Good, Piecewise is Precise": A way to remember the hierarchy of diode models.

Examples & Applications

Memory Aids

Interactive tools to help you remember key concepts

Glossary