Evidence for atomic scale disorder in indium nitride from perturbed angular correlation spectroscopy

The crystal lattice of bulk grains and state-of-the-art films of indium nitride was investigated at the atomic scale with perturbed angular correlation spectroscopy using the ¹¹¹In/Cd radioisotope probe. The probe was introduced during sample synthesis, by diffusion and by ion implantation. The mean quadrupole interaction frequency ν_Q ≤ 28 MHz was observed at the indium probe site in all types of indium nitride samples with broad frequency distributions. The observed small, but non-zero, asymmetry parameter indicates broken symmetry around the probe atoms. Results have been compared with theoretical calculations based on the point charge model. The consistency of the experimental results and their independence of the preparation technique suggest that the origin of the broad frequency distribution is inherent to indium nitride, indicating a high degree of disorder at the atomic scale. Due to the low dissociation temperature of indium nitride, furnace and rapid thermal annealing at atmospheric pressure reduce the lattice disorder only marginally.