Shallow Donors in Diamond: Chalcogens, Pnictogens, and their Hydrogen Complexes

The utility of diamond as an electronic material is compromised by the lack of a suitable shallow donor. Here, ab initio theory is used to investigate the donor levels of substitutional pnictogen (N, P, As, and Sb) and chalcogen (S, Se, and Te) impurities and chalcogen-hydrogen defects in diamond. Substitutional S is found to be a deep donor, while As and Sb possess donor levels significantly shallower than P, which so far is the most effective shallow donor found by experiment.

Figure 1

Sites for the H atom in defect-hydrogen complexes in diamond. The substitutional defect $X_s$ is shown in dark gray, while C and H atoms are light gray and white, respectively. The H atom is shown in three positions: Antibonded to the defect, ${\mathrm{H}}_{\mathrm{a}\mathrm{b}}$; Antibonded to a C neighbor of the defect, ${\mathrm{H}}_{\mathrm{a}\mathrm{b}}^{\mathrm{C}}$; At the middle of a $X_s$–C bond, ${\mathrm{H}}_{\mathrm{b}\mathrm{c}}$.

Figure 2

Band structure diagram showing the highest occupied electronic bands for As and P substitutional defects, together with the conduction band states for defect-free bulk diamond. The three band structures have been aligned by their valence band maxima at the $\Gamma$ point. The zero of the energy scale corresponds to the bulk diamond conduction band minimum.