Annealing behaviors of vacancy-type defects in AlN deposited by radio-frequency sputtering and metalorganic vapor phase epitaxy studied using monoenergetic positron beams

Abstract

Vacancy-type defects in AlN films were probed by using monoenergetic positron beams. The AlN films were deposited on sapphire substrates by using a radio-frequency sputtering technique. Epitaxial films grown by metalorganic vapor phase epitaxy on the sputtered AlN films were also characterized. For the sputtered AlN, the major defect species was identified to be complexes between Al-vacancy and oxygen atoms located at nitrogen sites. Vacancy clusters were introduced after annealing at 1300 °C in the N 2 atmosphere but their concentration decreased with a higher annealing temperature. The vacancy-oxygen complexes, however, still existed in the AlN film after annealing at 1700 °C. For the AlN epitaxial films, the concentration of vacancy clusters increased as the growth temperature increased up to 1300 °C but it decreased with the post-growth annealing at 1700 °C.

Impurity diffusion in ion implanted AlN layers on sapphire substrates by thermal annealing

“…Major defects in the MOCVD-grown AlN layers are V Al (V N ) n and V Al (O N ) n . 21) From the results of the V Al -related defects and impurity distribution after annealing, we suggest that the high oxygen concentration is the dominant reason that inhibits the electrical conduction of AlN layers on sapphire substrates. Oxygen atoms substitute nitrogen sites, forming complexes with aluminum vacancies V Al -O N with the stable deep acceptor level.…”

“…Singlecrystal Al 2 O 3 is decomposed at 1500 °C in a helium ambient at the rate of ∼2 nm min −1 . 21) We consider that oxygen atoms diffused from the decomposed Al 2 O 3 substrate into the AlN layer during annealing at 1600 °C. The silicon implanted AlN layer after annealing at 1250 °C was electrically conductive at the 2 × 2 mm 2 area, while that after annealing at 1600 °C was electrically insulative in the whole area.…”

Control of Metal‐Rich Growth for GaN/AlN Superlattice Fabrication on Face‐to‐Face‐Annealed Sputter‐Deposited AlN Templates

“…The large peak at ≈350 nm originated from oxygen‐related defects in the FFA Sp‐AlN layer of the AlN template substrates. [ 30 ] However, the AlN layer regrown by MOVPE has adequately reduced impurity concentration, [ 31 ] as explained in Section 2. Therefore, the defects in FFA Sp‐AlN layer did not affect the MBE growth.…”

“…After 180 nmthick AlN was deposited by RF sputtering (Sp-AlN) on c-plane sapphire substrates with an offcut of 0.2°in the [100] direction, face-to-face annealing (FFA) was performed at 1700 °C [28] Thereafter, AlN with a thickness of 200 nm was grown by MOVPE [29] FFA Sp-AlN includes high density of impurities and sometimes have bunched steps and/or small islands at the step edges on the surface. Therefore, an atomically flat surface with low impurity concentration was obtained using thermal cleaning and succeeding MOVPE regrowth [30,31] This AlN template was used as the substrate. The AlN template substrates had a full-width at half-maximum value of the X-ray rocking curve (XRC-FWHM) of <12 arcsecs on the (0002) plane and <260 arcsecs on the {101 ¯2} plane.…”

Epitaxial Junction of Inversion Symmetry Breaking AlN and Centrosymmetric NbN: A Polarity Control of Wide-Bandgap AlN

“…In the aforementioned studies, N-polar AlN was obtained via an oxygen-mediated growth mechanism. However, oxygen becomes an impurity in AlN and acts as a point defect, such as a radiative or nonradiative recombination center . Such point defects should be eliminated from AlN because they degrade the performance of light-emitting devices, wavelength conversion devices, and transistors.…”