Intrinsic and Extrinsic semiconductor
Extrinsic and intrinsic semiconductors are two categories of semiconductor materials that differ in terms of their electrical properties and the presence of impurities. Let's explore both types in detail:
Intrinsic Semiconductor: An intrinsic semiconductor is a pure semiconductor material with no intentional impurities added. It consists of a single element from the periodic table, such as silicon (Si) or germanium (Ge). Intrinsic semiconductors have the following characteristics:
Band Gap: Intrinsic semiconductors have a natural energy band gap between their valence band and conduction band. This band gap is relatively small, allowing electrons to move from the valence band to the conduction band when they gain sufficient thermal energy. However, at absolute zero temperature (0 Kelvin), the valence band is fully populated with electrons, and the conduction band is empty.
Electron-Hole Pairs: At temperatures above absolute zero, some electrons in the valence band gain enough energy to jump to the conduction band, creating electron-hole pairs. These electron-hole pairs are essential for electrical conductivity, as electrons can move in the conduction band, and holes (missing electrons) can move in the valence band. This allows for both electron and hole conductivity.
Limited Conductivity: Intrinsic semiconductors have moderate electrical conductivity, as they rely on thermally generated electron-hole pairs. Their electrical properties are strongly temperature-dependent, with higher temperatures leading to increased conductivity.
Extrinsic Semiconductor: \An extrinsic semiconductor, also known as a doped semiconductor, is a semiconductor material intentionally "doped" with specific impurities to modify its electrical behavior. Extrinsic semiconductors are typically used in electronic devices. There are two main types of extrinsic semiconductors:
1. N-Type Semiconductor: In an N-type semiconductor, small amounts of donor impurities are added to the pure semiconductor material. Common donor impurities include elements like phosphorus or arsenic. These donor impurities have more valence electrons than the semiconductor material, and they introduce extra electrons into the crystal lattice. As a result:
N-type semiconductors have excess free electrons, which are mobile charge carriers responsible for electron conductivity.
The majority charge carriers are electrons, and the minority charge carriers are holes.
N-type semiconductors are negatively charged due to the presence of extra electrons.
2. P-Type Semiconductor: In a P-type semiconductor, small amounts of acceptor impurities are added to the pure semiconductor material. Common acceptor impurities include elements like boron or gallium. These acceptor impurities have fewer valence electrons than the semiconductor material, creating "holes" or places where electrons are missing within the crystal lattice. As a result:
P-type semiconductors have excess holes, which are mobile charge carriers responsible for hole conductivity.
The majority charge carriers are holes, and the minority charge carriers are electrons.
P-type semiconductors are positively charged due to the presence of extra holes.
Extrinsic semiconductors can be engineered to have specific electrical properties, making them suitable for various electronic applications. They are the basis for the development of transistors, diodes, and integrated circuits, which form the foundation of modern electronics. The controlled introduction of impurities allows for precise control of conductivity, making extrinsic semiconductors an essential component of electronic devices.