Diamond Properties : Electrical Conductivity

Graphite conduct electricity while diamond does not. The difference in their appearances is one clue. The somewhat metallic luster of graphite announces its capacity to conduct electricity. Metals conduct electricity, while transparent substances, including diamond, are poor electrical conductors.

However, rare diamonds, particularly the gray-to-blue ones called type IIB, are semiconductors, and are somewhat conductive. Both diamond and graphite have important applications in electronics: Diamond may be used as either an insulator (nonconductor) or a semiconductor, and graphite is commonly used as a conductor.

Diamond is a semiconductor. In order for electrons to conduct electricity, they must overcome an energy barrier known as the band gap. This gap is defined as the energy difference between the valence band (lower energy) and the conduction band (higher energy). The valence band is filled with electrons, whereas the conduction band is empty. When the electrons obtain energy from an applied voltage, they can jump to the conduction band.

This is how semiconductors and insulators conduct electricity; their electrical conductivity is low (< 100 mho/ cm). The value of the band gap determines whether a substance is a semiconductor or an insulator. Scientists argue about where the breakoff point is, but generally semiconductors have band gaps around 5 eV (1 eV = 1.6x10e-19 J) or less. Hence, since diamond has a band gap of 5 eV, it is considered a wide-band-gap semiconductor.

A substance is an electrical conductor if very little energy is required to move an electron from its bonded condition in the so-called valence band to a mobile condition in the conduction band. Such conductors are metallic looking because light is moving the electrons, too.

In nonconductors (insulators) a large energy barrier exists between the valence band and the conduction band. This barrier must be "jumped" to allow conduction. Semiconductors such as type IIB diamonds have impurities that shrink the energy jump to the conduction band. These diamonds are moderate conductors of electricity.

Other Properties of Diamond.