Section 2.2: Semiconductors #

Semiconductors are special materials that make modern electronics possible. They’re special materials that can act as both a conductor (letting electricity flow) and an insulator (blocking electricity), depending on how they’re used. This unique property allows us to create all sorts of devices that control electricity in useful ways.

Diodes: One-Way Electronic Streets #

Key Information:

• A diode allows current to flow in only one direction
• The cathode lead (negative side) is often marked with a stripe
• The forward voltage drop is lower in some diode types than others

A diode has two electrodes:

• Anode: The positive connection
• Cathode: The negative connection, marked with a stripe

Think of a diode like a one-way street—current can only flow in one direction. But even when it’s flowing the right way, a diode doesn’t conduct perfectly. It takes a small amount of voltage just to get current moving; this is called the forward voltage drop (you might remember the concept of voltage drop from Section 1.2). That lost voltage turns into heat as electrical energy becomes thermal energy. Different types of diodes drop different amounts—for example, Schottky diodes typically have a lower forward voltage drop than regular silicon diodes.

One common use of diodes is in a rectifier, which changes alternating current (AC) into a varying direct current (DC) signal.

Light-Emitting Diodes (LEDs): Diodes That Shine #

Key Information: An LED produces light when forward current flows through it.

LEDs are special diodes that light up when current flows through them. They’re commonly used as indicator lights on radio equipment - that power light on your transceiver is an LED!

Transistors: The Heart of Modern Electronics #

Key Information:

• Transistors can be used as electronic switches
• Transistors can provide power gain (the ability to amplify signals)
• A transistor contains three regions of semiconductor material
• FET stands for Field Effect Transistor

There are two main types of transistors, and it’s important to know the names of their parts:

1. Bipolar Junction Transistor (BJT)

   • Three parts: Emitter, Base, and Collector
   • Often used for amplifying signals

2. Field-Effect Transistor (FET)

   • Three parts: Gate, Drain, and Source
   • Often used as voltage-controlled switches

Understanding Gain: When we talk about transistors providing “gain,” we mean their ability to amplify a signal - making a small signal bigger. This is one of their most important functions in radio equipment.

Integrated Circuits (ICs): Many Components in One #

Key Information: An integrated circuit combines several semiconductors and other components into one package.

Think of an IC as a tiny electronic city, where many components (transistors, diodes, resistors, etc.) work together in a single chip. This technology makes modern radio equipment possible by packing complex circuits into small spaces.

Semiconductor Review #

Let’s review the key semiconductor components and their main features:

1. Diodes

   • One-way current flow
   • Cathode marked with stripe
   • Different types have different voltage drops

2. LEDs

   • Light up with forward current
   • Used as indicators

3. Transistors

   • Three semiconductor regions
   • Two main types with different terminal names:
     • BJT: Emitter, Base, Collector
     • FET: Gate, Drain, Source
   • Can amplify signals (gain)
   • Can act as switches

4. Integrated Circuits

   • Multiple components in one package
   • Make complex circuits possible

Remember: While semiconductors can seem complex, understanding their basic functions and terminal names will help you both with the exam and in your amateur radio activities.