In general, semiconductors are inorganic or organic materials that can control their conduction depending on chemical structure, temperature, illumination, and the presence of dopants. The name semiconductor comes from the fact that these materials have electrical conductivity between a metal, like copper, gold, etc., and an insulator, like glass. They have an energy gap of less than 4eV (about 1eV). In solid-state physics, this energy gap or band gap is an energy range between the valence band and conduction band where electron states are forbidden. In contrast to conductors, semiconductors’ electrons must obtain energy (e.g., from ionizing radiation) to cross the band gap and reach the conduction band. The properties of semiconductors are determined by the energy gap between valence and conduction bands.
Silicon (Si) is the most widely used semiconductor material in the electronics industry. It has a bandgap of 1.1 electron volts (eV), which is an optimal value for electronic devices.
One of the main advantages of silicon is its abundance and low cost. Silicon is the second-most abundant element on Earth after oxygen and can be easily purified from sand or quartz. This makes it an ideal material for large-scale production of electronic devices.
Another advantage of silicon is its high stability and reliability, as it is not prone to impurities or other defects. This allows for consistent performance of electronic devices over a wide range of operating conditions.
Silicon also has excellent mechanical properties, such as high strength and hardness, which makes it a suitable material for use in microelectromechanical systems (MEMS).
In addition, silicon can be easily processed into thin films and integrated with other materials to form complex structures, which makes it ideal for use in microelectronics and integrated circuits.
However, one of the limitations of silicon is its relatively low electron mobility compared to other semiconductor materials such as gallium arsenide and gallium nitride. This limits its performance in high-frequency and high-power electronic devices.
Overall, silicon remains the backbone of the semiconductor industry due to its abundance, low cost, and reliability, and it will likely continue to be the dominant material for the foreseeable future.
Types of Semiconductors
Semiconductors can be classified into two basic types based on their electronic properties:
- Intrinsic Semiconductors: These are pure semiconductors that are made up of a single element (e.g., Silicon, Germanium) and have no intentional doping with impurities. Intrinsic semiconductors have a specific number of electrons in their valence band and conduction band. They conduct electricity when they are heated, and some electrons gain sufficient energy to break free from their bonds and become free electrons in the conduction band.
- Extrinsic Semiconductors: These are impure semiconductors that are intentionally doped with impurities to change their electronic properties. Extrinsic semiconductors can be further classified into two types:
- p-type semiconductors: In p-type semiconductors, impurity atoms such as boron are introduced into the semiconductor material. These impurities have fewer valence electrons than the semiconductor material, which results in “holes” (absence of electrons) being created in the valence band. These holes can conduct current like positive charge carriers, which gives the material its p-type designation.
- n-type semiconductors: In n-type semiconductors, impurity atoms such as phosphorus are introduced into the semiconductor material. These impurities have more valence electrons than the semiconductor material, which creates excess electrons in the conduction band. These excess electrons can conduct current like negative charge carriers, which gives the material its n-type designation.
Here is a table with 3 intrinsic semiconductors and 2 p-type and n-type semiconductors, along with 4 key properties:
|Band Gap (eV)
|Electron Mobility (cm²/Vs)
|Hole Mobility (cm²/Vs)
|Thermal Conductivity (W/mK)
|Gallium Arsenide (GaAs)
|Boron-doped Silicon (p-Si)
|Phosphorus-doped Silicon (n-Si)
|Aluminum-doped Gallium Arsenide (p-GaAs)
|Silicon-doped Gallium Arsenide (n-GaAs)