**1. Introduction**

Each time the creation and refinement of new material growth techniques give rise to the finding of new equipment. The semiconductor which has been found to be most interesting of all (when used), relates to the applications in electronic devices for instance, high speed circuits formed of group III-V compounds along with switches or amplifiers. One of the types of is the Gallium Arsenide (GaAs) [1, 2]. A III-V semiconductor that it is, its composition includes gallium which is an element of the group 3 having orthorhombic trigonal crystal structure coupled with arsenic which belongs to the group 5 and has a trigonal crystal structure. This very combination leads to interesting physical as well as chemical properties in this semiconductor [3, 4]. With different electronic band gaps, these semiconductors can, at ambient temperatures, crystalize into a zinc-blende cubic type crystal structure. Post the discovery of transistor in the year 1947, Gallium arsenide (GaAs) has presented itself as a prominent material for electronic devices. The technological importance and the need of study of Gallium arsenide (GaAs) in the last few years are due to its high melting point at 1238° C along with a density of 5.3176 g/cm3. It is obtained as a by-product from the extraction of ores of zinc and aluminum and is present at 5-15 mg/Kg in Earth's crust [5, 6].

GaAs is the basis of a worldwide industry it has a wide usage area changing from microwave frequency integrated circuits to optical windows. Among III-V semiconductors, GaAs has remained useful as a semiconductor material, widely being used in optoelectronic and microelectronic devices. Given this wide use of GaAs, the idea came to write this chapter focusing on the physical and chemical properties of this important material. While excluding the impurities present and their associated effects, the focus is on the characteristics of GaAs [7, 8].

Included in this chapter, are a few physical as well as chemical properties of gallium arsenide (GaAs) such as the crystal Structure, the direct bandgap of GaAs with its zinc blende type crystal structure, electronic structure, light-emitting

properties, electromagnetic properties, photovoltaic properties, phase transition and mechanical as well as elastic properties. The geometric structures, stabilities, and electronic properties like higher saturated electron velocity and high carrier mobility with a small dielectric constant and high resistivity. This chapter also elaborates on the thermodynamic properties of GaAs such as thermal expansion and thermal conduction.

These great properties led to the production of new and unique devices like high-efficiency light emitters, light sensors, and high-speed switching devices. The GaAs is considered as an outstanding member of the III-V semiconductor family. It has many exceptional features, especially for the recent optoelectronic industry. Hence, special focus has been laid on the examination of physical properties of this material [9–11].
