Examples of semiconductors include silicon (Si), germanium (Ge), gallium arsenide (GaAs), gallium nitride (GaN), indium phosphide (InP), and silicon carbide (SiC).
Properties of Semiconductors
Carrier Mobility in Semiconductor
Band Theory of Semiconductors
Band theory in semiconductors explains how electrons are arranged in energy bands. The valence band contains electrons tightly bound to atoms, while the conduction band holds electrons that can move freely. The energy gap between these bands is called the band gap, which is denoted in the unit of electron volts (eV). Below is a table that shows the energy band gap values of different semiconductors at 300 K.
- Electrons: These are negatively charged carriers that can move through the semiconductor material, contributing to electric current. Electron mobility refers to how easily electrons can move through a semiconductor material when subjected to an electric field. The higher the electron mobility, the faster the electronic device with better performance.
- Holes: These are the absence of an electron in the valence band, effectively acting as positively charged carriers. When an electron leaves its position in the valence band, it leaves behind a hole that can move as neighboring electrons jump to fill it. Hole mobility represents the movement of holes within a semiconductor lattice. The behavior of charge carriers within semiconductors is essential for optimizing their performance. To understand how charge carriers are created and responsible for conducting electricity, let us delve into semiconductor band theory. When thermally excited, electrons can jump from the valence band to the conduction band, creating electron-hole pairs. These charge carriers are responsible for electrical conductivity in semiconductors.
Types of Semiconductor
Doping in Semiconductors
Applications of Semiconductor
Extrinsic Semiconductors: They are doped with impurities to enhance their conductivity. By adding specific atoms like phosphorus or boron to the crystal lattice of the semiconductor material, engineers can increase the number of charge carriers and modify its electrical properties. The next section discusses doping in extrinsic semiconductors. This interplay between intrinsic properties and extrinsic modifications allows precise control over semiconductor behavior. N-type: This doping type involves adding elements such as phosphorus or arsenic to a semiconductor material like silicon. These elements have one extra electron compared to silicon atoms, making them donors of electrons. When these donor atoms are introduced into the semiconductor crystal lattice, they release free electrons into the material, increasing its electron concentration. This excess of negatively charged electrons gives rise to an N-type semiconductor with high electron conductivity. P-type: This doping type involves adding elements like boron or gallium to silicon. These elements have one less electron than silicon atoms, creating “holes” in the crystal lattice where an electron is missing. These “acceptor” atoms attract nearby electrons, creating spaces for new electrons to move in – effectively creating positively charged holes that behave as charge carriers. This results in a P-type semiconductor with increased hole concentration and enhanced hole conductivity.
