Native and radiation induced point defects in AlN and Sc-doped AlN (original) (raw)

Concentration of point defects in wurtzite AlN: A hybrid functional study

EPL (Europhysics Letters), 2012

Formation energies and concentrations of the most relevant point defects in n-type wurtzite AlN are obtained by first-principle calculations employing a hybrid functional. We show that the incorporation of Si is favoured over O under N-rich growth conditions, but not under Alrich conditions. The triply negatively charged Al vacancy is found to be the defect with the lowest formation energy in n-type AlN and it is therefore expected to be the main compensating acceptor. Under typical physical vapor-phase transport growth conditions, we predict Si concentrations of up to 10 20 cm −3 and net donor concentrations of about 10 18 cm −3 ,i ng o o da g r e e m e n tw i t ha v a i l a b l e experimental data.

Theoretical investigation of native defects, impurities, and complexes in aluminum nitride

Physical Review B, 2002

We have performed density-functional pseudopotential calculations to investigate the electronic structure, atomic configurations, and formation energies of native point defects and impurities in AlN. For the native defects, the nitrogen vacancy has the lowest formation energy in p-type material and the aluminum vacancy has the lowest formation energy in n-type material. Under n-type conditions the formation energy of the nitrogen vacancy is high, indicating that it will not occur in high concentrations. We find that the nitrogen vacancy exhibits a different behavior in the zinc-blende and wurtzite structures with respect to the higher-lying defectinduced level: in zinc-blende materials, this level is a resonance in the conduction band causing the vacancy to act as a shallow donor, while in wurtzite the level lies well below the conduction-band edge causing the vacancy to act as a deep donor. In the zinc-blende structure we find, in addition, that the aluminum interstitial has a low formation energy in p-type material. The results indicate that these defects could be important compensation centers; we discuss this in relation to the dopant impurities O, Si, and Mg. We also investigate MgO and Mg 2 O 2 impurity complexes. A comparison between results obtained using the local-density approximation and the generalized-gradient approximation for the exchange-correlation functional shows that the results are qualitatively very similar.

Charged vacancy defects in an AlN nanosheet: A first-principles DFT study

Computational Condensed Matter, 2018

Charged vacancy defects in an AlN nanosheet are studied by first principles calculations. Formation energies values at valence band maximum indicate that the nitrogen vacancy is more stable than the aluminum vacancy in both Al and N rich conditions. Under Al-rich and N-rich conditions, aluminum vacancy presents two transition levels in the band gap: from neutral state to a negative charge-state − (0/ 1), and from a negative charge-state to a double negative charged state − − (1/ 2). Nitrogen vacancy at low Fermi energies prefers a positive charged state, then it adopts a neutral charged state, and finally it is stabilized in a negative charge-state. Bond lengths of atoms in vicinity of vacancy and electronic structure are affected by charge states. AlN sheet with vacancy defects could present spin-polarized charge states. Magnetism originated by charged vacancy defects in AlN sheets can serve for potential applications in new spintronic devices.

Defects at nitrogen site in electron-irradiated AlN

Applied Physics Letters, 2011

In high resistance AlN irradiated with 2 MeV electrons, an electron paramagnetic resonance ͑EPR͒ spectrum, labeled EI-1, with an electron spin S = 1 / 2 and a clear hyperfine ͑hf͒ structure was observed. The hf structure was shown to be due the interaction between the electron spin and the nuclear spins of four 27 A nuclei with the hf splitting varying between ϳ6.0 and ϳ7.2 mT. Comparing the hf data obtained from EPR and ab initio supercell calculations we suggest the EI-1 defect to be the best candidate for the neutral nitrogen vacancy in AlN.

Ion-beam-produced damage and its stability in AlN films

2002

Structural characteristics of single-crystal wurtzite AlN epilayers ͑grown on sapphire substrates͒ bombarded with 300 keV 197 Au ϩ ions at room and liquid-nitrogen temperatures ͑RT and LN 2 ͒ are studied by a combination of Rutherford backscattering/channeling spectrometry and cross-sectional transmission electron microscopy. Results reveal extremely strong dynamic annealing of ion-beam-generated defects in AlN. Lattice amorphization is not observed even for very large doses of keV heavy ions at LN 2. An increase in irradiation temperature from LN 2 to RT has a relatively small effect on the production of stable structural damage in AlN. In contrast to the case of Al x Ga 1Ϫx N with xр0.6, neither damage saturation in the crystal bulk ͑below the random level͒ nor preferential surface disordering is revealed for AlN. Results also show that structural lattice disorder produced in AlN by high-dose keV heavy-ion bombardment is stable to rapid thermal annealing at temperatures as high as 1000°C.

EELS investigation of the electron conduction-band states in wurtzite AlN and oxygen-doped AlN(O)

Physical Review B, 1998

The electronic structures of pure and oxygen-doped AlN thin foils, grown by the chemical-vapor-deposition technique, have been thoroughly investigated using electron energy-loss measurements in a transmission electron microscope. This technique offers the advantage of providing spectral data with a typical sub-1-eV energy resolution from well-characterized areas. The interpretation of the experimentally determined electron energyloss near edge requires the detailed comparison with theoretical calculations of unoccupied densities of states using self-consistent methods or from non-self-consistent multiple scattering calculations. ͓S0163-1829͑98͒11131-1͔