ABSTRACT

Solids are usually divided into metals and nonmetals, with the nonmetals comprised of insulators and semiconductors. They may be grouped by their resistivity, ρ, which may range between 10-8 Ω-cm (metals) to 1018 Ω-cm (insulators) as illustrated in Figure 1.1. Semiconductors are intermediate

between the conductors and insulators and typically have resistivities between 10-2 Ω-cm and 108 Ω-cm. Virtually all inorganic and many organic materials belong to this group. The metals comprise those materials with very low resistivities (∼10-6 Ω-cm). However, within this group, some have resistivities that are quite high-in fact ∼102 to 103 times that of canonical metals, such as Cu. For this reason, metals such as As, Bi, and Sb are known as semi-metals. At the other end of the resistivity scale, the distinction between insulators and semiconductors can be somewhat vague, because some widegap materials that were previously regarded as insulators are now consi dered semiconductors (e.g., diamond). Because conductivity is a strong function of temperature, the difference between an insulator and a semiconductor really depends on the temperature at which the material’s properties are being evaluated. We can qualitatively define a semiconductor as a material that displays a noticeable electrical conductivity at, or above, room temperature. A true insulator, on the other

hand, will either melt or sublime before noticeable conductivity can be measured (e.g., quartz).