Group-II acceptors in wurtzite AlN: A screened hybrid density functional study

Szabó, Áron; Son, N. T.; Janzén, Erik; Gali, Ádám

doi:10.1063/1.3429086

Cited by 40 publications

(35 citation statements)

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“…The χ 2 [ Fig.2(a)-(c)] displays clear minima for displacements from the ideal S Al sites of at most 0.1Å. At first sight, if one assumes that all the substitutional Mg dopants in our samples are in the neutral state, our results seem to support the prediction of Szabó et al 12 and contradict that of Lyons et al 17 : if an elongation of Mg-N c-axis bond length does occur, it must be accommodated by a displacement of the N neighbor, without significantly displacing the Mg atom from the ideal Al site. On the other hand, if all substitutional Mg acceptors in our samples are in the ionized state (compensated by native donor defects, possibly created upon 27 Mg implantation), our results are perfectly consistent with the prediction of Lyons et al 17 , i.e.…”

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confidence: 81%

“…The shift results from the localization of the Mg-related hole on a N neighbor along the c-axis, which leads to an increase in the Mg-N bond length by 18% (0.34Å), accommodated by displacements of both the Mg atom and its N neighbor (along the c-axis). On the other hand, the ab initio calculations of Szabó et al 12 suggest for the acceptor state elongations of the Mg-N bond lengths by ∼0.2Å along the c-axis and ∼0.13Å basal to it, which should result in only small displacements of Mg from the ideal Ga site. These inconsistencies, which in fact also exist for Mg in GaN, [17][18][19] can only be clarified by a precise experimental determination of the Mg lattice location.…”

mentioning

confidence: 99%

“…Theoretical predictions regarding the best choice of acceptor for AlN differ considerably: while many favor Be on Al sites (Be Al ) 5,7-9 others have argued that Mg Al should be the most suitable acceptor. [10][11][12] So far, acceptor behavior has been claimed experimentally for Mg Al with an ionization energy around 500-630 meV, 4,13,14 as well as for Be Al with ∼330 meV. 15 In most theoretical work, only substitutional Mg Al on ideal Al sites has been considered, since interstitial Mg, which acts as donor, 16 was suggested to be unstable.…”

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confidence: 99%

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Precise lattice location of substitutional and interstitial Mg in AlN

Amorim

Wahl

Pereira

et al. 2013

Applied Physics Letters

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The lattice site location of radioactive 27Mg implanted in AlN was determined by means of emission channeling. The majority of the 27Mg was found to substitute for Al, yet significant fractions (up to 33%) were also identified close to the octahedral interstitial site. The activation energy for interstitial Mg diffusion is estimated to be between 1.1 eV and 1.7 eV. Substitutional Mg is shown to occupy ideal Al sites within a 0.1 Å experimental uncertainty. We discuss the absence of significant displacements from ideal Al sites, in the context of the current debate, on Mg doped nitride semiconductors.

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confidence: 81%

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confidence: 99%

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confidence: 99%

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Precise lattice location of substitutional and interstitial Mg in AlN

Amorim

Wahl

Pereira

et al. 2013

Applied Physics Letters

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“…This model worked very well for other defects in AlN. 9 We applied density functional theory calculations by choosing the PerdewBurke-Ernzerhof ͑PBE͒ functional. 10 Plane waves with a cut-off of 420 eV were utilized for the valence electrons together with PAW potentials.…”

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confidence: 99%

Defects at nitrogen site in electron-irradiated AlN

Son

Gali

Szabó

et al. 2011

Applied Physics Letters

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In high resistance AlN irradiated with 2 MeV electrons, an electron paramagnetic resonance (EPR) spectrum, labeled EI-1, with an electron spin S=1/2 and a clear hyperfine (hf) 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 similar to 6.0 and similar to 7.2 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.Original Publication:Nguyen Son Tien, A. Gali, A. Szabo, M. Bickermann, T. Ohshima, J. Isoya and Erik Janzén, Defects at nitrogen site in electron-irradiated AlN, 2011, Applied Physics Letters, (98), 24, 242116.http://dx.doi.org/10.1063/1.3600638Copyright: American Institute of Physicshttp://www.aip.org

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“…Recent theoretical calculations suggest that Mg is the shallowest acceptor of the group II elements [105]. However, Mg has a rather high activation energy, about 200 meV for GaN [106] and ~500-630 meV for AlN [10,107], which results in a low doping efficiency.…”

Section: Mg Doping Of Alganmentioning

confidence: 99%

Doping of high-Al-content AlGaN grown by MOCVD

Nilsson¹

2014

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The high-Al-content Al x Ga 1-x N, x > 0.70, is the principal wide-band-gap alloy system to enable the development of light-emitting diodes operating at the short wavelengths in the deep-ultraviolet, λ < 280 nm. The development of the deep-ultraviolet light-emitting diodes (DUV LEDs) is driven by the social and market impact expected from their implementation in portable units for water/surface disinfection and based on the damaging effect of the deep-ultraviolet radiation on the DNA of various microorganisms. Internationally, intense research and technology developments occur in the past few years, yet, the external quantum efficiency of the DUV LEDs is typically below 1%.One of the main material issues in the development of the DUV LEDs is the achievement of n-and ptype high-Al-content Al x Ga 1-x N layers with low resistivity, which is required for the electrical pumping of the diodes. The doping process becomes significantly more complex with increasing the Al content and the electrical resistivity is as high as 10 1 -10 2 Ω . cm for n-type AlN doped by silicon, and 10 7 -10 8 Ω cm for p-type AlN doped by magnesium.The present study was therefore focused on gaining a better understanding of the constraints in the doping process of the high-Al-content Al x Ga 1-x N alloys, involving mainly silicon. For this purpose, the epitaxial growth of the high-Al-content Al x Ga 1-x N and AlN by implementing the distinct hot-wall MOCVD was developed in order to achieve layers of good structural and morphological properties, and with low content of residual impurities, particularly oxygen and carbon. Substitutional point defects O N and C N may have a profound impact on the doping by their involvement in effects of ntype carrier compensation. The process temperature was varied between 1000 and up to 1400 °C, which is a principal advantage in order to optimize the material properties of the high-Al-content Al x Ga 1-x N and AlN. The epitaxial growth of the high-Al-content Al x Ga 1-x N and AlN was largely performed on 4H-SiC substrates motivated by (i) the lattice mismatch of ~ 1% along the basal plane (the smallest among other available substrates including Si and sapphire), (ii) the good thermal conductivity of 3.7 W cm -1 K -1 , which is essential to minimize the self-heating during the operation of any light-emitting diode, and (iii) the limited access to true-bulk AlN wafers. The outcome of this study is accordingly summarized and presents our understanding for (i) the complex impact of silicon and oxygen on the n-type conductivity of Al 0.77 Ga 0.23 N, representative for the alloy composition at which a drastic reduction of the n-type conductivity of Al x Ga 1-x N is commonly reported (paper 1); (ii) the strain and morphology compliance during the intentional iv doping by silicon and magnesium, and its correlation with the resistivity of highly doped layers of Al 0.82 Ga 0.18 N alloy composition (paper2); (iii) the n-type conductivity of highly Si-doped Al 0.72 Ga 0.28 N as bound by the process temperature (p...

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Group-II acceptors in wurtzite AlN: A screened hybrid density functional study

Abstract: We systematically studied the group-II acceptors in wurtzite AlN by screened hybrid density functional calculations. We show that the shallowest isolated group-II substitutional defect is Mg, while codoping of Mg and O may yield even shallower acceptor level.

Cited by 40 publications

References 33 publications

Precise lattice location of substitutional and interstitial Mg in AlN

Precise lattice location of substitutional and interstitial Mg in AlN

Defects at nitrogen site in electron-irradiated AlN

Doping of high-Al-content AlGaN grown by MOCVD

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