According to the structure of the GaAs Cell, each GaAs cell contains four as atoms and four Ga atoms, so the chemical formula of GaAs is GaAs. N, P and As are the same main group elements, and their hydride structures are similar. The higher the relative molecular weight is, the greater the intermolecular force is, and the higher the boiling point is. However, because hydrogen bonds can be formed between NH3 molecules, and the boiling point is abnormally high, the order of the boiling point of the hydride is NH 3 > ash 3 > pH 3. As and GA are in the same period and belong to the group of V A and III a respectively. The p orbital of as is in a half filled stable state, so the first ionization energy is AS > GA. The cell structure of GaAs is different from that of NaCl; In the cell of GaAs, each GA atom connects four as atoms to form a regular tetrahedron; Combined with the analysis of GA , the position of as in the periodic table shows that its electronegativity is as > GA; In the crystal cell of GaAs, each GA atom forms four covalent bonds with four as atoms. Because there are only three electrons in the outermost layer of GA atom, the electron pair of one covalent bond is completely provided by as atoms, forming a coordination bond.
In the presence of excess arsenic, GaAs boules grow with crystallographic defects; specifically, arsenic antisite defects (an arsenic atom at a gallium atom site within the crystal lattice). The electronic properties of those defects (interacting with others) cause the Fermi level to be pinned to close the middle of the band gap, in order that this GaAs crystal has very low concentration of electrons and holes. This low carrier concentration is analogous to an intrinsic (perfectly undoped) crystal, but much easier to realize in practice. These crystals are called "semi-insulating", reflecting their high resistivity of 107–109 Ω·cm (which is sort of high for a semiconductor, but still much less than a real insulator like glass).
Structural model for the Ga (or Al)‐rich GaAs(100)‐(2*1) surface and for the As‐rich (2*4) surface are examined. The foremost stable (2*1) surface includes an half monolayer of Ga vacancies,it makes the surface nonmetallic and nonpolar. For the (2*4) surface, unit cells include various combinations of As2 dimers, missing dimers, and Ga vacancies were considered. The foremost likely surface structure contains 3 As2 dimers per unit . Two such structures, nearly degenerate in energy, are possible. The calculated surface electronic structures accept as true with photoemission data to within ±0.3 eV. The c(2*8) and (2*4) structures are closely related and both are expected to occur at the surface.