First-principles calculations of the electronic structure and defects of Al2O3

Liu, Dameng; Guo, Yuxue; Lin, Lillian; Robertson, John

doi:10.1063/1.4818475

Cited by 29 publications

(40 citation statements)

References 36 publications

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“…[1][2][3][4][5] For this reason, native defects in Al 2 O 3 have been the subject of extensive experimental and theoretical investigations aiming at verifying the presence of deep-level traps in the dielectric. [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] The vast majority of theoretical studies performed so far have focused on crystalline phases of Al 2 O 3 . However, Al 2 O 3 in MOS devices is usually deposited via atomic layer deposition, which results in an amorphous phase with electronic properties differing considerably from those of crystalline phases.…”

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confidence: 99%

Oxygen defects in amorphous Al2O3: A hybrid functional study

Guo

Ambrosio

Pasquarello

2016

Applied Physics Letters

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The electronic properties of the oxygen vacancy and interstitial in amorphous Al 2 O 3 are studied via ab initio molecular dynamics simulations and hybrid functional calculations. Our results indicate that these defects do not occur in amorphous Al 2 O 3 , due to structural rearrangements which assimilate the defect structure and cause a delocalization of the associated defect levels. The imbalance of oxygen leads to a nonstoichiometric compound in which the oxygen occurs in the form of O 2− ions. Intrinsic oxygen defects are found to be unable to trap excess electrons. For low Fermi energies, the formation of peroxy linkages is found to be favored leading to the capture of holes. The relative +2/0 defect levels occurs at 2.5 eV from the valence band. in MOS devices is usually deposited via atomic layer deposition, which results in an amorphous phase with electronic properties differing considerably from those of crystalline phases. [21][22][23][24] Furthermore, the experimental characterization of defect states in a-Al 2 O 3 has led to conflicting interpretations. The oxygen vacancy has been invoked as an electron trap in oxygen-deficient a-Al 2 O 3 films on the basis of electron energy loss, photoluminescence, and capacitance measurements, and this suggestion has received support from theoretical studies based on density-functional-theory calculations. 6,21 At variance,Århammar et al. 7 synthesized a-Al 2 O 3 via physical vapour deposition and investigated the defect states in the gap using X-ray absorption and resonant inelastic scattering techniques. Supplementing their experimental results with computational studies, they assigned the observed defect states to peroxy linkages between two oxygen atoms (O-O) rather than to oxygen vacancies.In order to elucidate the nature of oxygen-related defects in a-Al 2 O 3 , we here investigate the structural and electronic properties of oxygen vacancies (V O ) and interstitials (O i ) in a-Al 2 O 3 through ab initio molecular dynamics (MD) simulations and hybrid functional calculations. We find that structural rearrangements in the amorphous can assimilate oxygen vacancies in the +2 charge state and oxygen interstitials in the −2 charge state removing any electronic state from the band gap. While excess electrons cannot be trapped by intrinsic oxygen defects, the presence of excess holes results in the formation of peroxy linkages, with defect states in the band gap at 2.5 eV from the valence band.All the calculations are carried out with the freely available CP2K suite of codes, 25 which is based on the use of atomic a) Electronic mail: zhendong.guo@epfl.ch basis sets and of a plane-wave expansion for the electron density. Analytical Goedecker-Teter-Hutter pseudopotentials 26 are used to account for core-valence interactions. We use a triple-ζ correlation-consistent polarized basis set 27 for O atoms, and the shorter range molecularly optimized doublezeta basis set with one polarization function 28 for Al atoms. For the plane-waves, a cutoff of 500 Ry is employed. The ...

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confidence: 99%

Oxygen defects in amorphous Al2O3: A hybrid functional study

Guo

Ambrosio

Pasquarello

2016

Applied Physics Letters

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“…The above model of defect energy alternating with charging status is supported by the first-principle calculation in Al 2 O 3 and ab initio calculations in GeO 2 [29][30][31], suggesting that EADs are intrinsic in Al 2 O 3 /GeO 2 /Ge structure.…”

Section: A Differences In Defect Energy Distribution In Ge and Simentioning

confidence: 70%

A Comparative Study of Defect Energy Distribution and Its Impact on Degradation Kinetics in GeO₂/Ge and SiON/Si pMOSFETs

Zhang

et al. 2016

IEEE Trans. Electron Devices

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Abstract-High mobility germanium (Ge) channel is considered as a strong candidate for replacing the Si in pMOSFETs in near future. It has been reported that the conventional power-law degradation kinetics of Si devices is inapplicable to Ge. In this work, further investigation is carried out on defect energy distribution, which clearly shows that this is because the defects in GeO 2 /Ge and SiON/Si devices have different physical properties. Three main differences are: 1) Energy alternating defects (EAD) exist in Ge devices but insignificant in Si; 2) The distribution of as-grown hole traps (AHT) has a tail in the Ge band gap but not in Si, which plays an important role in degradation kinetics and device lifetime prediction; 3) EAD generation in Ge devices requires the injected charge carriers to overcome a 2 nd energy barrier, but not in Si. Taking the above differences into account, the power law kinetics of EAD generation can be successfully restored by following a new procedure, which can assist in the Ge process/device optimization.

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“…43 Similarly, for α-Al 2 O 3 , they reported most interestingly in our terms, that V O and Al i are the dominant defect types located at ∼ 4.1 eV and ∼ 1.9 eV below CBM, respectively, and also transition levels due to Al dangling bonds at ∼ 2.8 eV below CBM. 44 45 However, the latter value also suffered from an underestimation of the bandgap being only 6.2 eV. As we expect to get primarily amorphous alumina from our plasma oxidation process, this latter value is the most important reference here.…”

Section: Kmc-results For Al/alo X /Aumentioning

confidence: 98%

“…Moreover, our barrier height must only be increased by ∼0.15 eV to obtain the "effective" value from experiments, as stated already by Weinberg earlier. 29 45 and the plasma process is likely to form an amorphous oxide. Another possible explanation would be the forming of alumina polymorphs, including several phases of Al 2 O 3 , which exhibit also several energies for the dominant V O or Al i , as cited above.…”

Section: Kmc-results For Al/alo X /Aumentioning

confidence: 99%

Kinetic Monte Carlo of transport processes in Al/AlOx/Au-layers: Impact of defects

et al. 2016

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Ultrathin films of alumina were investigated by a compact kMC-model. Experimental jV-curves from Al/AlOx/Au-junctions with plasma- and thermal-grown AlOx were fitted by simulated ones. We found dominant defects at 2.3-2.5 eV below CBM for AlOx with an effective mass mox∗=0.35 m0 and a barrier EB,Al/AlOx≈2.8 eV in agreement with literature. The parameterization is extended to varying defect levels, defect densities, injection barriers, effective masses and the thickness of AlOx. Thus, dominant charge transport processes and implications on the relevance of defects are derived and AlOx parameters are specified which are detrimental for the operation of devices.

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First-principles calculations of the electronic structure and defects of Al2O3

Cited by 29 publications

References 36 publications

Oxygen defects in amorphous Al2O3: A hybrid functional study

Oxygen defects in amorphous Al2O3: A hybrid functional study

A Comparative Study of Defect Energy Distribution and Its Impact on Degradation Kinetics in GeO₂/Ge and SiON/Si pMOSFETs

Kinetic Monte Carlo of transport processes in Al/AlOx/Au-layers: Impact of defects

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First-principles calculations of the electronic structure and defects of Al2O3

Cited by 29 publications

References 36 publications

Oxygen defects in amorphous Al2O3: A hybrid functional study

Oxygen defects in amorphous Al2O3: A hybrid functional study

A Comparative Study of Defect Energy Distribution and Its Impact on Degradation Kinetics in GeO2/Ge and SiON/Si pMOSFETs

Kinetic Monte Carlo of transport processes in Al/AlOx/Au-layers: Impact of defects

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A Comparative Study of Defect Energy Distribution and Its Impact on Degradation Kinetics in GeO₂/Ge and SiON/Si pMOSFETs