Perturbed angular correlation measurements of the hyperfine interaction of 111 In in sapphire show, that after implantation and annealing at 1000-C, the fraction of undisturbed probe atoms exhibiting a unique quadrupole interaction with # Q = 219(1) MHz (h = 0) varies between 50% at 4 K, 5% at 100 K and 80% at 973 K in a reversible manner. A possible explanation for this surprising behaviour is the influence of so-called Fafter effects_ following the EC-decay of 111 In to 111 Cd. Immediately after the decay the 111 Cd is in an ionized state, then collects electrons from its surroundings and reaches the ground state. The different electronic configurations that arise during this relaxation process affect the amplitude ( f u ) and the damping (d u ) of the unique quadrupole interaction.

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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 111 In/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.

GaN films were implanted with Er and Eu ions and rapid thermal annealing was performed at 1000, 1100 and 1200 ºC in vacuum, in flowing nitrogen gas or a mixture of NH 3 and N 2 . Rutherford backscattering spectrometry in the channeling mode was used to study the evolution of damage introduction and recovery in the Ga sublattice and to monitor the rare earth profiles after annealing. The surface morphology of the samples was analyzed by scanning electron microscopy and the optical properties by room temperature cathodoluminescence (CL). Samples annealed in vacuum and N 2 already show the first signs of surface dissociation at 1000 ºC. At higher temperature, Ga droplets form at the surface. However, samples annealed in NH 3 +N 2 exhibit a very good recovery of the lattice along with a smooth surface. These samples also show the strongest CL intensity for the rare earth related emissions in the green (for Er) and red (for Eu). After annealing at 1200 ºC in NH 3 +N 2 the Eu implanted sample reveals the channeling qualities of an unimplanted sample and a strong increase of CL intensity is observed.

Hyperfine interaction studies by means of the perturbed angular correlation technique have been carried out on In implanted into GaN and AlN. After the implantation of the probe 111In with 160 keV and annealing of the radiation damage for 120 s at 1273 K, it is found, that in both materials 50–60% of the In probes occupy regular lattice sites at room temperature. The remaining second fraction is found in a quite different but relatively well defined lattice environment. The regular fraction increases at the cost of the second fraction to approx. 100% at a sample temperature of 600 K in GaN and 900 K in AlN. The effect is completely reversible, i.e. the fractions change back to their previous values if the sample is measured again at room temperature. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)