Nitrogen donor excitation spectra in 3C-SiC

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Abstract
Infrared transmission spectra of high-quality vapor-grown 3C-SiC in the region of 1s-2p donor excitation transitions reveal three sequences of donor transitions analogous to those found in donor-doped silicon and germanium. Two of these sequences, a broad sequence and a sharp one, occur when the sample is held near 4.2 K. The broad sequence is assigned to transitions arising from the 1s(A) ground state of nitrogen. On warming, a second broad sequence, assigned to transitions from the 1s(E) ground state of nitrogen, is observed. The measured separation of these sequences, the 1s(A)-1s(E) valley-orbit splitting, is 8.34 meV. Excellent correspondence with theory is found for a nitrogen binding energy of 54.2 meV, consistent with other optical determinations of the nitrogen donor binding energy, and a static dielectric constant of 9.8. The sharp sequence, similar to sharp sequences found in very pure germanium, is attributed to an unidentified second donor whose excitation transitions are not broadened by grown-in local strain, e.g., an impurity free of chemical shift.