Sound velocity of AlxGa1−xN thin films obtained by surface acoustic-wave measurements

Değer, Caner; Born, E.; Angerer, H.; Ambacher, O.; Stutzmann, M.; Hornsteiner, J.; Riha, E.; Fischerauer, Gerhard

doi:10.1063/1.121368

Cited by 256 publications

(109 citation statements)

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“…As implied by its definition, d↔ is relevant to electroacustic applications [3], and to the determination of polarization and electrostatic fields induced by applied stress or strain in devices or epitaxial nanostructures [4].The piezoelectric tensor e ↔ [1,5] connecting polarization and strain ǫ i viais related to the d ↔ tensor of interest here bywhere the C ij are the elastic stiffness constants at constant electric field. It is thus possible to compute d ↔ from the knowledge of elastic constants and e-piezoconstants (using e.g.…”

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confidence: 99%

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First-principles calculation of the piezoelectric tensor d⇊ of III–V nitrides

Bernardini¹,

Fiorentini²

2002

Applied Physics Letters

136

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We report direct first-principles density-functional calculations of the piezoelectric tensor d The piezoelectric tensor d ↔ of a polar material relates to linear order the induced polarization P to the applied stress viaIt is an especially relevant quantity in the field of III-V nitride compounds, whose piezoelectric and polarization properties are prominent [1] and unusual [2]. As implied by its definition, d↔ is relevant to electroacustic applications [3], and to the determination of polarization and electrostatic fields induced by applied stress or strain in devices or epitaxial nanostructures [4].The piezoelectric tensor e ↔ [1,5] connecting polarization and strain ǫ i viais related to the d ↔ tensor of interest here bywhere the C ij are the elastic stiffness constants at constant electric field. It is thus possible to compute d ↔ from the knowledge of elastic constants and e-piezoconstants (using e.g. the theoretical estimates of Refs.[5] and [6], see also below). On the other hand, experiments [7][8][9][10][11][12] directly access the d ij measuring the strain ǫ i caused by an applied field E via the converse piezoelectric effectThe d ij 's in Eqs. 1 and 4 are by definition identical [13], so that a direct comparison is possible, and especially interesting and useful. Here we compute directly the d ij constants in the III-V binary nitrides as derivatives of the polarization with respect to stress, calculating the Berryphase polarization of a primitive cell explicitly subject to a given external stress. This approach enables us to directly compare the calculated values with experiment, and with indirect theoretical predictions using Eq. 3, and separately calculated C ↔ and e ↔ tensors. The binary III-V nitrides AlN, GaN, and InN crystallize in the wurtzite structure, and they possess three independent components of the piezoelectric tensor, namely d 33 , d 31 (=d 32 ), and d 15 (=d 24 ). To compute these constants we run a damped Parrinello-Rahman-like dynamics [14,15] for each of the compounds considered, with the constraint that the system be subject to a given non-zero stress. The external stress is applied to the zero-stress equilibrium structure, which is identical to that reported in Ref. [5]. As a compromise between the contrasting needs for sufficiently large stresses to obtain polarizations outside the numerical noise, and for sufficiently small stresses to avoid large deformations and non-linearity, we separately apply stress components σ 1 = σ 2 = ±50 Kbar in the basal plane, and σ 3 = ±50 Kbar along the singular axis, to determine d 31 and d 33 ; for d 15 we apply a shear stress σ 5 = ±50 kBar. In the case of InN, these stresses and the ensuing deformations may lead to metallization because of the very small calculated DFT band gap. This must be avoided because macroscopic polarization cannot be defined or computed in metallic systems. We found that the maximum applied stress had to be reduced to 5 Kbar for InN (incidentally, this does not causes numerical noise problems in the polarization cal...

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mentioning

confidence: 99%

“…↔ is relevant to electroacustic applications [3], and to the determination of polarization and electrostatic fields induced by applied stress or strain in devices or epitaxial nanostructures [4].…”

mentioning

confidence: 99%

First-principles calculation of the piezoelectric tensor d⇊ of III–V nitrides

Bernardini¹,

Fiorentini²

2002

Applied Physics Letters

136

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“…With an oscillation period of 2 ps, the traveling time in the OPT is 4.4 ps, resulting in 21.0 ps traveling time in the GaN cap layer. Assuming the sound velocity of GaN along c-axis is 8020 m/s [27], the thickness of the GaN cap layer is thus estimated to be ∼84 nm.…”

Section: One-dimensional Scan Measurementmentioning

confidence: 99%

Optical piezoelectric transducer for nano-ultrasonics

Lin

Chern

et al. 2005

IEEE Trans. Ultrason., Ferroelect., Freq. Contr.

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Abstract-Piezoelectric semiconductor strained layers can be treated as piezoelectric transducers to generate nanometer-wavelength and THz-frequency acoustic waves. The mechanism of nano-acoustic wave (NAW) generation in strained piezoelectric layers, induced by femtosecond optical pulses, can be modeled by a macroscopic elastic continuum theory. The optical absorption change of the strained layers modulated by NAW through quantum-confined Franz-Keldysh (QCFK) effects allows optical detection of the propagating NAW. Based on these piezoelectric-based optical principles, we have designed an optical piezoelectric transducer (OPT) to generate NAW. The optically generated NAW is then applied to one-dimensional (1-D) ultrasonic scan for thickness measurement, which is the first step toward multidimensional nano-ultrasonic imaging. By launching a NAW pulse and resolving the returned acoustic echo signal with femtosecond optical pulses, the thickness of the studied layer can be measured with <1 nm resolution. This nano-structured OPT technique will provide the key toward the realization of nano-ultrasonics, which is analogous to the typical ultrasonic techniques but in a nanometer scale.

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“…The SAW velocities in GaN-on-sapphire systems, which are proportional to centre frequencies of SAW filters, are sensitive to the GaN-layer thickness because elastic properties in GaN are different from those in sapphire (velocity dispersion) [5,7]. Furthermore, in general, there remains a run-to-run variation of several percents in actual thicknesses of epitaxially-grown GaN layers with the fixed nominal thicknesses.…”

Section: Introductionmentioning

confidence: 99%

“…AlGaN/GaN field-effect transistors have been successfully applied to dual-gate mixers [2] as well as to L-or K-band power amplifiers [3,4]. Recently, (Al)GaN-based surface acoustic wave (SAW) devices have been investigated for the purpose of exploiting both the marked piezoelectric properties and semiconducting characteristics of group-III nitrides [1,5,6,7,8]. Change in filter characteristics due to ultraviolet illumination [9] and that due to DC bias voltages [10] have also been examined.…”

Section: Introductionmentioning

confidence: 99%

Velocity dispersion in GaN-based surface acoustic wave filters on (0001) sapphire substrates

Shigekawa

Nishimura

Yokoyama

et al. 2005

IEICE Electron. Express

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Abstract:We fabricated surface acoustic wave (SAW) filters on three nominally 2-µm-thick undoped GaN layers grown on (0001) sapphire substrates. We extracted SAW velocities for frequencies of the central and subsidiary peaks in the |S 21 | spectra by applying the δ-function model. We further obtained thicknesses of respective GaN layers by analysing their reflectivity spectra, and established the SAW velocity dispersion. The respective dispersion data were found to lie close to each other, which suggests that characteristics of GaN-based SAW devices can be designed with improved accuracy. Keywords: GaN, sapphire, surface acoustic wave, SAW, velocity dispersion Classification: New functional devices and materials References[1] O. Ambacher, "Growth and applications of Group III nitrides," J. Phys. D: Appl. Phys., vol. 31, no. 20, pp. 2653-2710, Oct. 1998

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Sound velocity of AlxGa1−xN thin films obtained by surface acoustic-wave measurements

Cited by 256 publications

References 14 publications

First-principles calculation of the piezoelectric tensor d⇊ of III–V nitrides

First-principles calculation of the piezoelectric tensor d⇊ of III–V nitrides

Optical piezoelectric transducer for nano-ultrasonics

Velocity dispersion in GaN-based surface acoustic wave filters on (0001) sapphire substrates

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