Background Information for Understanding Semiconductors

When examining the flow of electricity through a circuit, resistivity plays a crucial role. Resistance is defined as the ratio of voltage across a component to the current flowing through it, a principle known as Ohm’s Law. Simply put, this law states that if the resistance of a conductor remains constant, an increase in voltage results in a proportional increase in current.
However, resistance alone is not an ideal measurement because it depends on the physical dimensions and composition of a material. For instance:

• Increasing a material’s length raises its resistance.
• Increasing its diameter lowers its resistance.

To better quantify a material’s ability to conduct or resist electrical current, we use resistivity, denoted by the Greek symbol ρ (rho), measured in Ohm-meters (Ωm). Resistivity is the inverse of conductivity and helps classify materials into three categories:

• Conductors - Materials with low resistivity, allowing easy electrical flow.
• Insulators - Materials with high resistivity, preventing electrical flow.
• Semiconductors - Materials with resistivity between that of conductors and insulators.

Resistivity Chart

These are just a few of the most common materials used in electronic components.

Conductors have the lowest resistivity values, allowing electrical current to flow easily due to the abundance of free electrons in their atomic structure. However, these electrons require an external force—voltage—to move. When voltage is applied, free electrons leave their parent atoms and drift through the material, generating electrical current.

Good conductors include copper, aluminum, silver, and even some non-metals like carbon, which have loosely bound electrons in their outer valence shell. This enables electrons to move freely, creating a domino effect that facilitates current flow.

In contrast, insulators have very few or no free electrons available for conduction. Their tightly bound electrons remain strongly attracted to the nucleus, making it extremely difficult for current to pass through. Additionally, insulators are generally unaffected by temperature changes.

Common insulators include glass, quartz, PVC plastics, rubber, and marble. They play a critical role in electrical circuits, preventing unintended short circuits and ensuring components function properly.

Semiconductors, such as silicon (Si), germanium (Ge), and gallium arsenide (GaAs), have electrical properties that fall between conductors and insulators. Their atoms are arranged in a crystalline lattice structure, allowing limited electron flow under specific conditions.

The conductivity of semiconductors can be significantly enhanced by introducing impurities, a process called doping. This involves adding donor or acceptor atoms to the crystal lattice, increasing the number of free electrons (negative charge carriers) or holes (positive charge carriers).

• Intrinsic Semiconductors - Pure silicon or germanium without impurities.
• Extrinsic Semiconductors - Doped materials classified as either:
• Semiconductors - Materials with resistivity between that of conductors and insulators.
  • N-Type (Negative Type): Contains extra electrons.
  • P-Type (Positive Type): Contains extra holes.

By precisely controlling the doping process, semiconductor materials can be engineered for use in diodes, transistors, and other essential electronic components.

Understanding these fundamental concepts is crucial for anyone working with semiconductors. At TEDSS.com, we are committed to providing quality components and the knowledge needed to use them effectively.