Dynamical-charge neutrality at a crystal surface

Ruini, Alice; Resta, Raffaele; Baroni, Stefano

doi:10.1103/physrevb.57.5742

Cited by 25 publications

(25 citation statements)

References 15 publications

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“…We have shown in Ref. [17] how to regolarize such an indeterminate sum using the appropriate physical criterion: to the present purposes, suffices to say that the dynamical neutrality of the interface, discussed above, is the crucial property ensuring the correct result.…”

Section: Figmentioning

confidence: 96%

“…We have recently discovered a novel sum rule for the dynamical charges at the surface of a semi-infinite crystal, [17] which is easily generalized to the case of an interface between a pair of semiinfinite crystals. The present (001) geometry is a particularly simple example, where the meaning of our sum rule can be made clear without any formal derivations.…”

Section: Figmentioning

confidence: 99%

“…Actual calculations performed for As-terminated Al/GaAs(001) show that the semiconductor Z * converge to their bulk value rather slowly: the actual thickness of the interface region, when monitored by means of Z * , is definitely larger than an analysis of the mere static electronic charge would suggest. Finally, owing to a novel sum rule, [17] the sum of all Z * in the interface region equals one half the bulk Z * value.…”

Section: Figmentioning

confidence: 99%

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Effects of interface morphology on Schottky-barrier heights: A case study on Al/GaAs(001)

1997

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The problem of Fermi-level pinning at semiconductor-metal contacts is readdressed starting from first-principles calculations for Al/GaAs. We give quantitative evidence that the Schottky barrier height is very little affected by any structural distortions on the metal side-including elongations of the metal-semiconductor bond (i.e. interface strain)-whereas it strongly depends on the interface structure on the semiconductor side. A rationale for these findings is given in terms of the interface dipole generated by the ionic effective charges.Despite several decades of extensive experimental and theoretical work, [1] the key factors affecting the Fermilevel pinning at metal-semiconductor contacts have not yet been clearly assessed. Since the microscopic morphology of the interface is not experimentally accessible, the controversy concerns even the very basic issue as to whether the pinning is determined by intrinsic interface states which exist even at an abrupt ideal interface, or by extrinsic electronic states arising from native defects. The experimental data are of little help in discriminating between different theoretical pictures, given that the value of the barrier for a given semiconductor depends very little on the nature of the metal, [1] and for a given metal/semiconductor pair it depends even less on the direction of growth. Ab initio calculations-though necessarily limited to rather idealized situations and affected by basic approximations necessary to cope with the complexity of the electronic many-body problem-allow instead, by their very nature, to have full control on the way the details at the atomic scale of a given system affect the various physical properties under investigation. In this sense, ab initio calculations are complementary to the experimental investigations and, in the specific case of metal-semiconductor contacts, they have in fact provided in recent year a great deal of quantititave information that any successful model will have to account for. [2][3][4][5][6][7][8] Because of this theoretical work, the following facts are now well established: the barrier height does depend of the nature of the metal; [2] it does depend on the crystallographic direction; and furthermore for a given crystallographic direction of growth it even depends on the microscopic morphology of the interface.[5] The electronic mechanisms governing the value of the Schottky barrier-as well as their variations as a function of the microscopic morphology of the interface-have not been systematically investigated so far and are basically unknown. Here we provide a contribution in this direction, by studying the barrier-height variations induced in Al/GaAs(001) by several structural and morphological perturbations which are switched on and off in our computational framework. Our calculations provide a microscopic probe for the nature of the interface-including its "effective" thickness-and for the electronic response phenomena responsible for the barrier height. The crucial role of the effective dynamical cha...

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Section: Figmentioning

confidence: 96%

Section: Figmentioning

confidence: 99%

Section: Figmentioning

confidence: 99%

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Effects of interface morphology on Schottky-barrier heights: A case study on Al/GaAs(001)

1997

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“…We notice that the dynamical charges in the surface region deviate considerably from their bulk value, although they converge rather fast to it. A corollary of the dynamical-neutrality theorem, as applied to the [001] geometry considered here, states the the sum of the dynamical charges in the surface planes must add up to one half of the corresponding bulk value (with the appropriate sign) [15]. This sum rule-which can be regarded as the surface analogue of the popular acoustic sum rule for the bulk [16]-is very accurately fullfilled by our calculations.…”

Section: Surface Dynamical Chargesmentioning

confidence: 68%

“…This fact implies-owing to a recently discovered theorem [15]-that the surface region must also be dynamically neutral. We notice that the dynamical charges in the surface region deviate considerably from their bulk value, although they converge rather fast to it.…”

Section: Surface Dynamical Chargesmentioning

confidence: 99%

Hartree-Fock studies of the ferroelectric perovskites

Fu¹,

Yaschenko²,

Resca³

et al. 1998

AIP Conference Proceedings

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Abstract. Within an ab-initio HF scheme, we use both Berry-phase calculations and supercell calculations in order to compute the dynamical charges for lattice dynamics and the electronic dielectric constant for KNbO 3 and BaTiO 3 . Comparison with experimental data indicates that HF provides a description of the electronic properties of this material whose accuracy is of the same order as the LDA one. There are however significant differences between the two sets of results, whose origin is scrutinized. Motivated by the study of surface and domain-boundary properties, we also present some results for BaTiO 3 slabs, including both genuinely isolated and periodically repeated slabs with different terminations. The capability of dealing with a genuinely isolated slab is a virtue of the localized-basis implementation adopted here. We demonstrate, amongst other things, the nontrivial dynamical-charge neutrality of BaTiO 3 [001] surfaces.

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Schottky Barrier Height in GaN/Al Junctions: an ab-initio Study

Picozzi¹,

Continenza²,

Massidda

et al. 2002

phys. stat. sol. (a)

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We performed ab-initio full-potential linearized augmented plane wave (FLAPW) calculations for [0001]-wurtzite and [111]-zincblende GaN/Al junctions, focusing on the Schottky barrier height. We propose a procedure to evaluate the potential discontinuity in the presence of electric fields, showing that their effect is relatively small (a few tenths of an eV). These calculations assess the rectifying behaviour of the GaN/Al contact, in agreement with experimental values for the barrier. IntroductionGaN has certainly been one of the most studied compounds in the last few years, mainly because of both interesting optical properties and remarkable thermal stability, which render this semiconductor particularly suitable for important technological applications. As it is well known, however, device performances depend on good metallic contacts and so the study of Schottky barrier heights (SBH) in GaN/ metal systems is of great relevance [1][2][3][4].Within this framework, we present results from first-principles calculations using the all-electron full-potential linearized augmented plane wave (FLAPW) method [5] for [0001] wurtzite (w-GaN/Al) and [111] zincblende (z-GaN/Al) GaN/Al interfaces. These systems can be directly compared, since the [111]-ordered zincblende (ZB) and [0001]-ordered wurtzite (WZ) structures have the same coordination up to the third nearestneighbor shell and the interface geometry (in terms of number and direction of bonds) is the same.

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Dynamical-charge neutrality at a crystal surface

Cited by 25 publications

References 15 publications

Effects of interface morphology on Schottky-barrier heights: A case study on Al/GaAs(001)

Effects of interface morphology on Schottky-barrier heights: A case study on Al/GaAs(001)

Hartree-Fock studies of the ferroelectric perovskites

Schottky Barrier Height in GaN/Al Junctions: an ab-initio Study

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