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The elastic strain and damage build-ups induced by 50 keV He implantations at elevated temperature in (0001)AlN were studied using a combination of X-ray diffraction, transmission electron microscopy and elastic recoil detection analysis experiments. No long-range migration of He atoms occurs up to 700°C. The point defect recombination is found to be enhanced with the increase of implantation temperature. When He concentration exceeds a determined temperature-dependent threshold, the stabilization of vacancies through the formation of He-vacancy clusters of critical size strongly enhances the interstitial concentration and elastic strain in proportion with the local He concentration. Above this threshold, for a critical He concentration that decreases from several at% at room temperature to a few tenths of at% at 700°C, bubbles form and induce a strong increase of disorder. Specific features observed at 700°C, including the systematic superimposition of bubble clusters with basal stacking faults, suggest the triggering between 550 and 700°C of a mechanism promoting disorder, which is discussed. • The mobility of point defects is increased from RT to 550°C, and from 550 to 700°C. • XRD is used to determine threshold He concentrations related to He-V clustering. • These thresholds are ascribed to the formation of He-V clusters of critical size. • Peculiar bubble growth and bubble cluster-BSF relationships are observed at 700°C. • A mechanism promoting disorder is triggered between 550 and 700°C. [ABSTRACT FROM AUTHOR]

The elastic strain build-up and damage induced by 50 keV He implantation at RT and 550 °C into (0001)AlN were studied using a combination of XRD experiments, XRD simulation, and TEM experiments. Evidence for strong dynamic annealing with efficient point defect recombination is reported at RT. The point defect recombination is found to be enhanced with increasing implantation temperature where He concentration is low, indicating increased mobility of interstitial-type defects and resulting in low strain. A reversed effect is observed for He concentration exceeding 5 at.% (3 at.%) at RT (550 °C) : thermally activated mechanisms related to the nucleation and growth of He-V complexes overcome the point defect recombination and promote the strain and damage build-up. At 1 × 1017 cm−2, only clusters of interstitials are observed at RT, whilst bubbles and basal stacking faults are additionally formed at 550 °C for a critical He concentration estimated to be close to 4–6 at.%. [ABSTRACT FROM AUTHOR]

He implantation was performed at RT and 550 °C into AlN epitaxial films. The resulting microstructural damage and elastic strain were investigated using TEM and XRD. Basal stacking faults, clusters of point defects and bubbles aligned along (0001) planes are observed at both temperatures. Apart from slight variations of size and densities of defects, no significant difference is observed on the microstructure after implantation at RT and 550 °C. In particular, He bubbles are observed with similar size, showing that the long-range migration of vacancies is not triggered at 550 °C. An important effect of He on the enhancement of damage and strain build-up during implantation is evidenced. He bubbles are observed to strongly favor the nucleation of extended defects, both basal stacking faults and point defect clusters, which results from the increase of free interstitial concentration due to stabilization of vacancies by He that could be enhanced by the bubble growth by loop punching or trap mutation to relieve the gas pressure. At an earlier stage of implantation-induced damage, the presence of He is also seen to induce a strong increase of strain with increasing implantation temperature, whilst efficient point defect recombination takes place in the regions free of He, or with low concentration of He, resulting in a decrease of strain. The strong increase of strain with increasing temperature in the deep implanted region, concomitant with a strong reduction of scattered intensity, is ascribed to the growth of He–V complexes, probably induced by a thermally enhanced mobility of He, and only occurs for sufficient He concentration. [ABSTRACT FROM AUTHOR]