Gallium Arsenide

Semiconductors

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.

Gallium Arsenide

Gallium arsenide (GaAs) is a semiconductor material that is used in a variety of electronic applications. It has several advantages over silicon, including higher electron mobility, higher operating frequencies, and better resistance to radiation damage.

In GaAs, the crystal structure is similar to that of silicon, but the bonds between the atoms are stronger, making it a more durable material. GaAs is also a direct bandgap material, meaning that it can efficiently convert electrical energy into light energy, which makes it ideal for use in optoelectronic devices such as LEDs and laser diodes.

GaAs is commonly used in high-speed electronic devices, such as microwave transistors and high-frequency integrated circuits, due to its high electron mobility. It is also used in solar cells and other photovoltaic devices because of its high absorption coefficient, which allows it to efficiently convert light energy into electrical energy.

Another advantage of GaAs is its high radiation hardness, which makes it well-suited for use in space and other high-radiation environments. This property is due to the fact that GaAs has a higher energy bandgap than silicon, which makes it more resistant to radiation-induced defects.

However, one of the main drawbacks of GaAs is its higher cost compared to silicon, which limits its use in many consumer electronics applications. Nevertheless, GaAs continues to be an important semiconductor material in many specialized applications where its unique properties provide significant advantages.

Types of Semiconductors

Semiconductors can be classified into two basic types based on their electronic properties:

1. 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.
2. 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:
   1. 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.
   2. 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:

Semiconductor	Type	Band Gap (eV)	Electron Mobility (cm²/Vs)	Hole Mobility (cm²/Vs)	Thermal Conductivity (W/mK)
Silicon (Si)	Intrinsic	1.12	1500	450	150
Germanium (Ge)	Intrinsic	0.67	3900	1900	60
Gallium Arsenide (GaAs)	Intrinsic	1.43	8500	400	46
Boron-doped Silicon (p-Si)	p-type	1.12	1500	1800	150
Phosphorus-doped Silicon (n-Si)	n-type	1.12	1500	4500	150
Aluminum-doped Gallium Arsenide (p-GaAs)	p-type	1.43	8500	200	46
Silicon-doped Gallium Arsenide (n-GaAs)	n-type	1.43	8500	800	46