Direct evidence for carbon incorporation on the nitrogen site in AlN

We use photo-electron paramagnetic resonance (EPR) measurements and first-principles calculations to identify and explain the properties of carbon in AlN. We present clear evidence for carbon substitution on the nitrogen site (${\mathrm{C}}_{\mathrm{N}}$). We also clarify the origin of a widely observed EPR spectra in AlN that, although often attributed to a deep donor defect, we demonstrate is surprisingly due to ${\mathrm{C}}_{\mathrm{N}}$. Finally, we show the presence of ${\mathrm{C}}_{\mathrm{N}}$ is consistent with the absorption spectra at 4.7 eV observed in AlN.