Structural and electronic properties of ideal nitride/Al interfaces

Picozzi, Silvia; Continenza, A.; Massidda, S.; Freeman, Arthur J

doi:10.1103/physrevb.57.4849

Cited by 30 publications

(33 citation statements)

References 61 publications

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“…For the interplane distance we consider the two values c/a =1.005, 1.01, which are experimentally determined for the SBMO at different temperatures [14]. For all the above parameters SBMO is safely in an AFM (G-type) insulating state with a band gap of ∼ 0.4 eV with Mn magnetic moments M ∼ 2.6 µ b , in agreement with previous DFT calculations on CaMnO 3 and SrMnO 3 [12,13,21] and experiments on SrMnO 3 [22]. The valence band is predominantly majority-spin Mn t 2g and O 2p characther with strong p−d hybridization while the conduction band is formed by Mn e g orbital and empty minority t 2g states, which is consistent with Mn…”

Section: Pacs Numberssupporting

confidence: 74%

Microscopic Origin of Large Negative Magnetoelectric Coupling inSr1/2Ba1/2MnO3

et al. 2012

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With a combined ab initio density functional and model Hamiltonian approach we establish that in the recently discovered multiferroic phase of the manganite Sr 1/2 Ba 1/2 MnO3 the polar distortion of Mn and O ions is stabilized via enhanced in-plane Mn-O hybridizations. The magnetic superexchange interaction is very sensitive to the polar bond-bending distortion, and we find that this dependence directly causes a strong magnetoelectric coupling. This novel mechanism for multiferroicity is consistent with the experimentally observed reduced ferroelectric polarization upon the onset of magnetic ordering. PACS numbers:Multiferroic materials are ideal candidates for the realization and practical use of strong magnetoelectric effects [1,2]. The scarcity of actual materials that are magnetic ferroelectrics appears to be related to the competition between the conventional mechanism of ferroelectric cation off-centering, which requires empty d-orbitals, and the formation of magnetic moments which requires partially filled d-orbitals [1,2]. A concomitance of magnetism and ferroelectricity then has to rely on more subtle microscopic coupling mechanisms, driven by spinorbit coupling in the form of Dzyaloshinskii-Moriya interactions [3] or exchange-striction [4]. The recently synthesized manganite Sr 1/2 Ba 1/2 MnO 3 however defeats the generic incompatibility of a cation both having a magnetic moment and being ferroelectrically displaced. This system is a classic example of a material in which charge, spin, lattice and orbital degrees of freedom are strongly coupled, giving in this particular case rise to a strong magnetoelectric (ME) effect, the origin of which we set out to clarify here.For doing so, the methods from modern ab initio bandstructure theory are powerfull tools -very helpful not only in predicting new multiferroic materials, but also in understanding the underlying mechanisms for magnetoelectric couplings. The computed values of macroscopic polarization P agree exceptionally well with those observed experimentally [5][6][7][8][9][10]. In the last few years several ab initio calculations have pointed out the possible ferroelectric state with large polarization for AMnO 3 , where A is an alkaline earth element. The proposed mechanism is based on off-centering of Mn 4+ ions stabilized via a charge-lattice coupling of Peierls type [11][12][13]. The problems in synthesizing such a material with predicted ferroelectricity has very recently been overcome: last year Sr 1/2 Ba 1/2 MnO 3 (SBMO) has been reported to support a ferroelectric phase via the off-centering of magnetic Mn 4+ ion in conjunction with a perovskite tetragonal structure [14]. The onset of the low-temperature long-range antiferromagnetic (AFM) ordering strongly reduces the polarization indicating a large magnetoelectric effect [14]. The AFM order, in other words, does not support ferroelectricity, but it neither completely destroys it. This special feature of SBMO opens a new avenue for the quest of materials with strong ME effects, where the searc...

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Section: Pacs Numberssupporting

confidence: 74%

Microscopic Origin of Large Negative Magnetoelectric Coupling inSr1/2Ba1/2MnO3

et al. 2012

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“…However, the data points towards a modification of the interface stoichiometry with an altered oxygen and Mn-content in this region [27,31,32]. Even a slight modification in the oxygen and Mn-concentration would result in a significant deviation of the Mn 3+ /Mn 4+ ratio.…”

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confidence: 89%

Element-specific depth profile of magnetism and stoichiometry at theLa0.67Sr0.33MnO3/BiFeO3

et al. 2014

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Depth-sensitive magnetic, structural and chemical characterization is important in the understanding and optimization of novel physical phenomena emerging at interfaces of transition metal oxide heterostructures. In a simultaneous approach we have used polarized neutron and resonant X-ray reflectometry to determine the magnetic profile across atomically sharp interfaces of ferromagnetic La 0.67 Sr 0.33 MnO 3 /multiferroic BiFeO 3 bi-layers with sub-nanometer resolution. In particular, the X-ray resonant magnetic reflectivity measurements at the Fe and Mn resonance edges allowed us to determine the element specific depth profile of the ferromagnetic moments in both the La 0.67 Sr 0.33 MnO 3 and BiFeO 3 layers. Our measurements indicate a magnetically diluted interface layer within the La 0.67 Sr 0.33 MnO 3 layer, in contrast to previous observations on inversely deposited layers [1]. Additional resonant X-ray reflection measurements indicate a region of an altered Mn-and O-content at the interface, with a thickness matching that of the magnetic diluted layer, as origin of the reduction of the magnetic moment.

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“…In particular, the SBH can be expressed as ⌽ B p ϭ⌬bϩ⌬E b , where ⌬b and ⌬E b indicate an ''interface'' and ''bulk'' contribution, respectively ͑see Ref. 22 for details in the GaN/Al case͒. This simple procedure is commonly used in ab initio all-electron calculations to evaluate the interface band line up at semiconductor heterojunctions or metal/semiconductor junctions.…”

Section: Computational Methods and Atomic Configurations Used In Cmentioning

confidence: 99%

“…We considered all the structures for a cubic ͑i.e., zincblende͒ ͓001͔ ordered GaN substrate, with a calculated lattice constant a subs ϭa GaN ϭ8.47 a.u.. 26 Further structural details can be found in Ref. 22. All the structures considered are shown in Fig.…”

Section: Computational Methods and Atomic Configurations Used In Cmentioning

confidence: 99%

“…In a previous work, 22 we performed ab initio calculations to determine the electronic properties of the ͓001͔ ordered atomically abrupt N-terminated XN/Al ͑XϭGa,Al͒ interface, focusing mainly on the Schottky barrier height and the resulting interface states. In the work reported here, the structural and electronic properties of several Al/GaN interface configurations are investigated.…”

Section: Introductionmentioning

confidence: 99%

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Influence of the exchange reaction on the electronic structure of GaN/Al junctions

Picozzi¹,

Continenza²,

Massidda

et al. 1998

Phys. Rev. B

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Ab initio full-potential linearized augmented plane-wave ͑FLAPW͒ calculations have been used to study the influence of the interface morphology and, notably, of the exchange reaction on the electronic properties of Al/GaN ͑100͒ interfaces. Although the detailed mechanism is not understood, the exchange reaction has been purported to influence the Schottky barrier height ͑SBH͒ as a result of the formation of an interfacial Ga x Al 1Ϫx N layer. In particular, the effects of interface structure ͑i.e., interfacial bond lengths, semiconductor surface polarity, and reacted intralayers͒ on the SBH at the Al/GaN ͑001͒ junction are specifically addressed. Thus, the electronic structure of the following atomic configurations have been investigated theoretically: ͑i͒ an abrupt, relaxed GaN/Al interface; ͑ii͒ an interface that has undergone one monolayer of exchange reaction; and interfaces with a monolayer-thick interlayer of ͑iii͒ AlN and ͑iv͒ Ga 0.5 Al 0.5 N. The exchange reaction is found to be exothermic with an enthalpy of 0.1 eV/atom. We find that the first few layers of semiconductor are metallic due to the tailing of metal-induced gap states; therefore, the presence of a monolayer-thick interfacial alloy layer does not result in an enhanced band gap near the interface. Intermixed interfaces are found to pin the interface Fermi level at a position not significantly different from that of an abrupt interface. Our calculations also show that the interface band lineup is not strongly dependent on the interface morphology changes studied. The p type SBH is reduced by less than 0.1 eV if the GaN surface is Ga terminated compared to the N terminated one. Moreover, we show that both an ultrathin Ga x Al 1Ϫx N ͑xϭ0, 0.5͒ intralayer and a Ga↔Al atomic swap at the interface do not significantly affect the Schottky barrier height.

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Structural and electronic properties of ideal nitride/Al interfaces

Cited by 30 publications

References 61 publications

Microscopic Origin of Large Negative Magnetoelectric Coupling inSr1/2Ba1/2MnO3

Microscopic Origin of Large Negative Magnetoelectric Coupling inSr1/2Ba1/2MnO3

Element-specific depth profile of magnetism and stoichiometry at theLa0.67Sr0.33MnO3/BiFeO3

Influence of the exchange reaction on the electronic structure of GaN/Al junctions

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