Editing Gallium arsenide (section)

===Semi-insulating crystals===
In the presence of excess arsenic, GaAs [[Boule (crystal)|boules]] grow with [[crystallographic defect]]s; specifically, arsenic antisite defects (an arsenic atom at a gallium atom site within the crystal lattice). The electronic properties of these defects (interacting with others) cause the [[Fermi level]] to be [[Fermi level pinning|pinned]] to near the center of the band gap, so that this GaAs crystal has very low concentration of electrons and holes. This low carrier concentration is similar to an intrinsic (perfectly undoped) crystal, but much easier to achieve in practice. These crystals are called "semi-insulating", reflecting their high resistivity of 10<sup>7</sup>–10<sup>9</sup> Ω·cm (which is quite high for a semiconductor, but still much lower than a true insulator like glass).<ref name="DD-2012">McCluskey, Matthew D. and Haller, Eugene E. (2012) ''Dopants and Defects in Semiconductors'', pp. 41 and 66, {{ISBN|978-1439831526}}</ref>