Ab initio supercell calculations on aluminum-related defects in SiC

Ab initio supercell calculations of the binding energies predict complex formation between aluminum and carbon interstitials in SiC. In high-energy implanted SiC aluminum acceptor can form very stable complexes with two carbon interstitials. We also show that carbon vacancy can be attached to shallow aluminum acceptor. All of these defects produce deep levels in the band gap. The possible relation of these defects to the recently found aluminum-related deep-level transient spectroscopy centers is discussed.

Figure 1

(Color online) Stablest complexes of ${\mathrm{Al}}_{\mathrm{Si}}{\left({\mathrm{C}}_{\mathrm{i}}\right)}_2$ in different charge states: (a) (−), (b) (+). Small cyan and big yellow and green balls depict carbon, silicon, and aluminum atoms, respectively. The localization of highest occupied defect state is shown: green (red) lobes represents the positive (negative) value of the wave function.

Figure 2

(Color online) Stablest complexes of ${\mathrm{Al}}_{\mathrm{i}}{\mathrm{C}}_{\mathrm{i}}$ in different charge states: (a) $(3+)$ (b) $(1+)$. The geometry of $(2+)$ is “halfway” in between that of $(3+)$ and $(1+)$. Small cyan and big yellow and green balls depict carbon, silicon, and aluminum atoms, respectively. The localization of highest occupied defect state is shown: green (red) lobes represents the positive (negative) value of the wave function.

Figure 3

(Color online) Metastable complexes of ${\mathrm{Al}}_{\mathrm{i}}{\mathrm{C}}_{\mathrm{i}}$ in different charge states: (a) $(3+)$ and (b) (+). Small cyan and big yellow and green balls depict carbon, silicon, and aluminum atoms, respectively. The localization of highest-occupied defect state is shown: green (red) lobes represents the positive (negative) value of the wave function.

Figure 4

(Color online) Stable complexes of ${\mathrm{Al}}_{\mathrm{i}}{\left({\mathrm{C}}_{\mathrm{i}}\right)}_2$ in different charge states: (a) (+), (b) $(2+)$ (c) $(3+)$. Small cyan and big yellow and green balls depict carbon, silicon, and aluminum atoms, respectively. The localization of highest-occupied defect state is shown: green (red) lobes represents the positive (negative) value of the wave function.

Figure 5

(Color online) Stable complexes of ${\mathrm{Al}}_{\mathrm{Si}}{V}_{\mathrm{C}}$ in different charge states: (a) (+), (b) (−), (c) $(3-)$. Small cyan and big yellow and green balls depict carbon, silicon, and aluminum atoms, respectively. The localization of highest occupied defect state is shown: green (red) lobes represents the positive (negative) value of the wave function. In (+) state there is no occupied defect level in the gap.