Anisotropic polaron localization and spontaneous symmetry breaking: Comparison of cation-site acceptors in GaN and ZnO

Sun, Yiyang; Abtew, Tesfaye A.; Zhang, Peihong; Zhang, S. B.

doi:10.1103/physrevb.90.165301

Cited by 16 publications

(12 citation statements)

References 39 publications

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“…For the isolated Li Zn and Na Zn acceptors, we find that both exhibit a dual behavior, as first reported by Lany and Zunger [27,28] using a Koopmans corrected semilocal functional, and later by Sun et al [56] using the HSE(0.375, [28]. In the neutral charge state, two distinct acceptor states can occur [27,28]: (i) a metastable shallow state, where the hole is bound in an anisotropically delocalized hostlike state [56], and (ii) a deep ground state, which can be reached through a sizable symmetry-breaking lattice distortion. As shown in Fig.…”

Section: A Formation Energies Thermodynamic Charge-state Transitionsupporting

confidence: 86%

Broad luminescence from donor-complexed LiZn and NaZn acceptors in ZnO

et al. 2019

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Zn substitutional lithium (Li Zn) and sodium (Na Zn) acceptors and their complexes with common donor impurities (Al Zn , H i , and H O) in ZnO have been studied using hybrid functional calculations. The results show that the complexes are not exclusively charge neutral, but rather exhibit a thermodynamic (+/0) transition level close to the valence band maximum. The positive charge states are associated with a polaronic defect state, similar to those of the well-studied charge-neutral isolated acceptors. This incomplete passivation has profound consequences for the optical properties of the complexes. Indeed, electron transitions from the conduction band minimum to the (+/0) transition level of the complexes result in broad luminescence bands that are blueshifted with respect to those originating from the isolated acceptors. Such complexes are proposed as a potential defect origin of the green luminescence observed at the high-energy side of the orange luminescence band (caused by Li Zn) in hydrothermally grown ZnO. This prediction is supported by experimental photoluminescence and secondary ion mass spectrometry data on a hydrothermally grown ZnO sample. We have also explored how the parameters controlling the fraction and screening of exchange in the Heyd-Scuseria-Ernzerhof (HSE) hybrid functional influence the results by comparing two parametrization approaches: (i) the conventional one where the exchange fraction is adjusted to reproduce the experimental band gap, and (ii) tuning both parameters in order to also comply with the generalized Koopmans theorem (gKT). Interestingly, these approaches were found to yield similar results.

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Section: A Formation Energies Thermodynamic Charge-state Transitionsupporting

confidence: 86%

Broad luminescence from donor-complexed LiZn and NaZn acceptors in ZnO

et al. 2019

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“…This is similar to other theoretical results obtained in Refs. [3][4][5]. Strongly localized nature of this small polaron leads to the predicted wide PL band, with the Franck-Condon shift of 0.43 eV, which is a signature of a deep defect state.…”

Section: B Why Localized Small Polaron States Of Mg Ga Are Not Obsermentioning

confidence: 88%

“…As mentioned above, three distinct defect states of neutral Mg Ga ,5 with different lattice configurations of similar energies are two localized small polarons and one anisotropically delocalized shallow state. The latter is delocalized in [ 1120 ] direction of wurtzite GaN and localized in all other directions.…”

mentioning

confidence: 79%

“…Other groups, employing hybrid density functional calculations, have found that the hole bound to the Mg Ga acceptor in the ground state is highly localized, with 0/− transition levels of 0.23 (optical transition at 2.7 eV) 3 and 0.38 eV, 4 however did not confirm the existence of the delocalized state. Recently Sun et al 5 have demonstrated that neutral Mg Ga 0 acceptor exhibits three different defect states. Two of these are localized defect-bound small polarons, characterized by a hole trapped by its self-induced lattice distortion, while the third is the anisotropically delocalized state, which is effective-mass-like in the [ 1120 ] direction and localized in all other directions.…”

Section: Introductionmentioning

confidence: 99%

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Magnesium acceptor in gallium nitride. II. Koopmans-tuned Heyd-Scuseria-Ernzerhof hybrid functional calculations of its dual nature and optical properties

2018

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The problem of magnesium acceptor in gallium nitride is that experimental photoluminescence measurements clearly reveal shallow defect state, while most theoretical predictions favor localized polaronic defect state. To resolve this contradiction, we calculate properties of magnesium acceptor using HSE hybrid functional, tuned to fulfill generalized Koopmans condition. We test Koopmans tuning of HSE for defect calculation in GaN using two contrasting test cases: a deep state of gallium vacancy and a shallow sate of magnesium acceptor. Thus, obtained parametrization of HSE allows calculations of optical properties of acceptors using neutral defect state eigenvalues, without relying on corrections due to charged defects in periodic supercells. Optical transitions and vibrational properties of Mg Ga defect are analyzed, to bring the dual (shallow and deep) nature of this defect into accord with experimental photoluminescence measurements of the ultraviolet band in Mg-doped GaN samples.

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“…They also predicted that the Li Zn defect in ZnO may have a dual nature, where, in addition to the deep localized state, a shallow acceptor state may exist at about 0.21 eV above the valence band and be revealed in certain experimental conditions [18]. DFT calculations based on hybrid functional schemes predicted a binding energy of 0.75 eV [19,20] and 0.46 eV [21] for the Li Zn acceptor in ZnO. Carvalho et al [22] concluded that, by using different pseudopotentials and functionals, the calculated binding energy of the Li Zn acceptor varies between 0.6 and 1.1 eV.…”

Section: Introductionmentioning

confidence: 97%

Abrupt and tunable quenching of photoluminescence in ZnO

McNamara¹,

Albarakati²,

Reshchikov³

2016

Journal of Luminescence

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a b s t r a c tThe abrupt and tunable quenching of photoluminescence (PL) in bulk ZnO samples is reported, a phenomenon which has been previously observed only in GaN and a few phosphorescent materials. ZnO samples grown by the hydrothermal method contain Li defects responsible for the orange luminescence (OL) band with a maximum at 2.0 eV. The Li Zn acceptor is well studied, but there is some disagreement in the literature on the value of its ionization energy. Here we show that the ionization energy of the Li Zn acceptor responsible for the OL band is 0.65 70.10 eV. The thermal emission of holes from the Li Zn acceptor to the valence band and their subsequent capture by unknown nonradiative centers causes the abrupt quenching of PL, the temperature of which is tunable by excitation intensity.Published by Elsevier B.V.

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Anisotropic polaron localization and spontaneous symmetry breaking: Comparison of cation-site acceptors in GaN and ZnO

Cited by 16 publications

References 39 publications

Broad luminescence from donor-complexed LiZn and NaZn acceptors in ZnO

Broad luminescence from donor-complexed LiZn and NaZn acceptors in ZnO

Magnesium acceptor in gallium nitride. II. Koopmans-tuned Heyd-Scuseria-Ernzerhof hybrid functional calculations of its dual nature and optical properties

Abrupt and tunable quenching of photoluminescence in ZnO

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