Defect identification in aluminum nitride through photo-EPR

The ultrawide bandgap semiconductor AlN has applications in high power microelectronic and optical devices. Studying the defects of AlN is essential in improving the material and understanding its functionality, as unwanted absorption due to a defect may impede the electrical properties. The identification of the defect and the energy at which a charge state transition of the defect occurs is the goal of this research. Photo-induced electron paramagnetic resonance (EPR) spectroscopy was performed on 7 x 2.3 x 0.5 mm pieces of AlN grown via physical vapor transport. The EPR signal has a g-value of 2.004 with the c-axis parallel to the applied magnetic field and is thought to be substitutional oxygen (O_N⁰), but our photo-EPR results suggest the defect is carbon on a nitrogen site (C_N⁰). The measurements were taken during illumination with varying photon energies at constant photon flux to determine thresholds for photoexcitation and photoquenching. The results show that the photo-threshold for quenching occurs between 1.2 eV to 1.7 eV, which agrees with theoretical predictions for a neutral to negative charge state transition of C_N, but differs from that predicted for transitions calculated for O_N.