Physical and electrical properties of silica

Nominally pure silica or amorphous SiO2 is an important material in modern electronics, as well as other fields of science. Normally, it has been utilized for its insulation properties, for example, in metal-oxide-semiconductor devices. However, it also can be considered as a wide bandgap semiconductor possessing very large electrical resistivity. The conductivity of various silica films has been studied since the mid-nineteenth century, usually assuming the presence of ionic conductivity. However, in the sense of a wide bandgap semiconductor, the temperature dependence of the resistivity, which ranges over more than four orders of magnitude, can be accurately explained by normal semiconductor behavior under the presumed presence of a deep electron trap/donor residing ∼2.3 eV below the conduction band edge. That is, the conductance is determined by electron motion and not by ions. Experiments have studied the transport of injected electrons (and holes) which are consistent with this viewpoint.