Emission channeling experiments from the decay of [formula omitted] to [formula omitted] in GaN

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The lattice site location of excited states of 149 Eu was studied by means of the emission channeling technique. The 60 keV implantation of 149 Tb into a GaN thin film was performed at room temperature up to a dose of 2.0×10 13 cm −2. This radioactive isotope eventually decays into short-lived excited states of 149 Eu . The conversion electrons emitted in the subsequent decay to the 149 Eu ground state were detected with a position sensitive detector. We measured their angular distributions around the [0 0 0 1], [ 1 ̄ 1 0 2 ], [ 1 ̄ 1 0 1 ] and [ 2 ̄ 1 1 3 ] axes in the as-implanted state and after 600 and 900 °C vacuum annealing. Already in the as-implanted state around 65% of 149∗ Eu atoms were found on substitutional Ga sites. The root mean square (rms) displacements from the substitutional sites in the as-implanted state were found to be around 0.13–0.16 Å. Annealing up to 600 °C increased the substitutional fraction by a few percent and slightly reduced the rms displacements, most likely due to the removal of crystal defects in the vicinity of the Eu atoms, resulting in a better incorporation into substitutional sites.