Semiconductors and Diodes

A comprehensive set of flashcards covering the fundamentals of semiconductors and diodes, including their properties, operations, and applications.

Foundation of modern electronic devices

Semiconductors.

Common semiconductor materials

Silicon and germanium.

Why silicon is the most widely used semiconductor

Because of its thermal stability and reliability.

Usefulness of a diode

It is useful for controlling electrical signals in circuits.

Formation of a PN junction diode

Created by joining two types of semiconductor materials.

How a P-type semiconductor is formed

Formed by adding impurities called acceptor atoms (such as boron) to pure silicon.

Majority charge carriers in P-type

Holes.

Minority charge carriers in P-type

Electrons.

How an N-type semiconductor is formed

Formed by adding donor atoms (such as phosphorus or arsenic).

Majority charge carriers in N-type

Electrons.

Minority charge carriers in N-type

Holes.

Initial movement of carriers at the junction

Electrons from the N-region move toward the P-region. Holes from the P-region move toward the N-region.

What happens to charges at the boundary?

These charges recombine near the boundary.

Contents of the depletion region

Immobile ions. No free electrons or holes.

What the electric field in the depletion region does

Prevents further movement of carriers.

Barrier Potential of a Silicon diode

0.7 V.

Barrier Potential of a Germanium diode

0.3 V.

What the operation of a diode depends on

How the external voltage is applied.

Forward bias connection

P-side connected to positive terminal. N-side connected to negative terminal.

Effect of external voltage on barrier potential in forward bias

External voltage reduces the barrier potential.

Effect on depletion region in forward bias

Depletion region becomes narrower.

Result of carriers in forward bias

Electrons and holes cross the junction.

Condition for strong conduction in forward bias

Once the applied voltage exceeds the barrier voltage (0.7 V for silicon).

Result of a diode in forward bias

The diode behaves like a closed switch allowing current flow.

Reverse bias connection

P-side connected to negative terminal. N-side connected to positive terminal.

Effect of external voltage on barrier potential in reverse bias

External voltage increases the barrier potential.

Effect on depletion region in reverse bias

Depletion region becomes wider.

Movement of majority carriers in reverse bias

Majority carriers move away from the junction.

Reverse leakage current

A very small current that flows due to minority carriers.

Result of a diode in reverse bias

The diode behaves like an open switch.

Purpose of diode equivalent models

To simplify circuit calculations.

Ideal Diode Model - Forward bias assumptions

Zero resistance. No voltage drop across the diode.

Ideal Diode Model - Reverse bias assumption

Infinite resistance.

Ideal Diode Model - Equivalent behavior

Forward bias → Short circuit. Reverse bias → Open circuit.

Practical Diode Model - Key characteristic

Real diodes have some voltage drop when conducting.

Practical Diode Model - Silicon forward voltage

0.7 V.

Practical Diode Model - Germanium forward voltage

0.3 V.

Practical Diode Model - Condition for conduction

The diode conducts only when the applied voltage exceeds the cut-in voltage.

Common uses of diodes in circuits

Rectification, signal clipping, switching, and protection.

Components of a half-wave rectifier

AC voltage source, diode, load resistor.

Half-Wave Rectifier - Positive half cycle operation

Diode becomes forward biased. Current flows through the load.

Half-Wave Rectifier - Negative half cycle operation

Diode becomes reverse biased. Current stops.

Half-Wave Rectifier - Output description

Only the positive half of the AC waveform appears at the output. This produces pulsating DC voltage.

LED - Movement of charges

Electrons move from the N-region. Holes move from the P-region.

LED - Process at the junction

They recombine at the junction. Energy is released as photons (light).

Name of the process in an LED

Electroluminescence.

LED Color for Gallium Arsenide

Red.

LED Color for Gallium Phosphide

Green.

LED Color for Gallium Nitride

Blue.

Four characteristics of LEDs

Low power consumption, fast switching speed, long operational life, small physical size.

Five applications of LEDs

Indicator lamps, digital displays, traffic lights, television screens, automotive lighting, decorative lighting.

Five advantages of PN Junction Diodes

Simple design, low cost, reliable operation, small size, high efficiency in rectification.