The Fermi level in diamond

Abstract

Diamond is a wide-band-gap material with large donor and acceptorionization energies. In principle, at room temperature andbelow, the Fermi energy is pinned close to the donor oracceptor level, depending on which is present in the higherconcentration. In semiconductors with shallow donors and acceptors the equilibrium charge states of defects aredetermined by the position of the Fermi level. However, in aninsulating material like diamond we show that the calculatedposition of the Fermi level does not necessarily predict thecorrect charge state of a defect, and propose instead that the charge state is influenced by the proximity of the defect to adonor (or acceptor). Qualitatively this accounts for thedependence of the charge state on the concentration of isolatedsubstitutional nitrogen and also explains why many opticalcentres can be present in two different charge states in thesame diamond.