Frequency gaps for acoustic phonons in<i>a</i>-Si:H/a-<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">SiN</mml:mi></mml:mrow><mml:mrow><mml:mi mathvariant="normal">x</mml:mi></mml:mrow></mml:msub></mml:mrow></mml:math>:H superlattices

Santos, P. V.; Ley, L.; Mebert, J.; Koblinger, O.

doi:10.1103/physrevb.36.4858

Cited by 60 publications

(15 citation statements)

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“…It was proposed a long time ago that the minigap of these zone-folded SL acoustical phonons could be used as a ''phonon filter,'' acting very much like dielectric BR's but for the selective reflection of high frequency sound waves [9,10]. Thus, a planar phonon cavity can be constructed by enclosing between two SL's a spacer of thickness equal to an integral number of ac =2, where now ac is the wavelength of the acoustical phonon at the center of the phonon minigap.…”

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confidence: 99%

Confinement of Acoustical Vibrations in a Semiconductor Planar Phonon Cavity

et al. 2002

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Extending the idea of optical microcavities to sound waves, we propose a phonon cavity consisting of two semiconductor superlattices enclosing a spacer layer. We show that acoustical phonons can be confined in such layered structures when the spacer thickness is an integer multiple of the acoustic half-wavelength at the center of one of the superlattice folded minigaps. We report Raman scattering experiments that, taking profit of an optical microcavity geometry, demonstrate unambiguously the observation of a phonon-cavity confined acoustical vibration in a GaAs/AlAs based structure. The experimental results compare precisely with photoelastic model calculations of the Raman spectra.

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confidence: 99%

Confinement of Acoustical Vibrations in a Semiconductor Planar Phonon Cavity

et al. 2002

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“…The second zone center mode, in contrast, causes only a very small reflectivity bump. The large difference in reflectivity for the two modes arises from the different phases x between the light electric field and the SAWinduced modulation of the optical thickness along x [11,12]. The latter are in phase (i.e., x 0) for the third mode, thus ensuring a strong coupling to the incident light beam.…”

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confidence: 99%

Phonon-Induced Optical Superlattice

et al. 2005

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We demonstrate the formation of a dynamic optical superlattice through the modulation of a semiconductor microcavity by stimulated acoustic phonons. The high coherent phonon population produces a folded optical dispersion relation with well-defined energy gaps and renormalized energy levels, which are accessed using reflection and diffraction experiments. DOI: 10.1103/PhysRevLett.94.126805 PACS numbers: 73.21.Cd, 42.65.Es, 42.70.Qs, 77.65.Dq The notion of a superlattice, a periodic stack of layers of different materials, was originally introduced as a way of tailoring the electronic band structure of semiconductors via quantum size effects [1]. The dispersion relation of elementary excitations in superlattices is characterized by minibands within a folded mini-Brillouin zone (MBZ) defined by the artificial periodicity and separated by minigaps corresponding to regions without propagating modes. The superlattice concept was later extended to phonons [2]. Although optical superlattices in the form of Bragg mirrors have been known for a long time, their two-and threedimensional counterparts, typically referred to as photonic crystals, are presently receiving considerable attention due to the ability to induce light localization and control spontaneous emission [3,4].Elementary excitations such as phonons, plasmons, and spin waves also create, when stimulated with a welldefined wave vector, a periodic modulation of the material's optical properties. In fact, this modulation provides a primary source of information about their energy dispersion when accessed using techniques such as Raman and Brillouin spectroscopy. An interesting question is whether an elementary excitation can create a dynamic optical superlattice with a folded dispersion and energy gaps. The interaction with photons, however, is usually very weak with induced energy shifts smaller than the characteristic width of the spectral lines. This interaction becomes enhanced for photon energies in resonance with the elementary excitation (resonant scattering) or by artificially increasing their population above the equilibrium (stimulated scattering). We point out that excitations of a bosonic nature are more appropriate for optical modulation with a high excitation density in order to avoid the broadening of the spectral features due to many-body effects [5]. The previous conditions may lead to the formation of new quasiparticles, as exemplified by the different forms of polaritons.The interaction with photons can be further enhanced in low-dimensional structures. Strong optical fields in semiconductor microcavities have been shown to increase the cross section for Raman scattering by thermal vibrations by several orders of magnitude [6]. In addition, Brillouin scattering efficiencies exceeding 40% have been reported in microcavities exposed to a high, nonthermal population of coherent acoustic modes [7]. A zone folded energy dispersion with minigaps has also been predicted for cavity polaritons modulated by coherent acoustic phonons [5]. To our knowl...

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“…Thus, semiconductor superlattices extensively used as distributed Bragg mirrors for photons can also act as high reflectance phonon mirrors in the GHz-THz range [20,36]. Thanks to the development of growth processes, it is possible to obtain large stackings of layers with a period of a few nanometers, and with interface fluctuations of one atomic monolayer.…”

Section: Principlementioning

confidence: 99%

Semiconductor superlattices: A tool for terahertz acoustics

2015

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The properties of optical to acoustic transduction of semiconductor superlattices have been explored for several years in the sub terahertz frequency range. Using femtosecond laser pulses focused on these structures, acoustic modes are excited with a frequency related to the periodicity of the structure stacking. We have shown that these acoustic waves can be extracted and can propagate in the underlying substrate. We study superlattices ability to be quasi monochromatic generators. On the other hand, superlattices have been found to be very sensitive and selective detectors. We present a set of experimental results concerning the generation, propagation over large distances and detection of acoustic waves at high frequencies, up to the challenging 1 THz by picosecond ultrasonics experiments in transmission geometry.

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Frequency gaps for acoustic phonons ina-Si:H/a-SiNx:H superlattices

Cited by 60 publications

References 14 publications

Confinement of Acoustical Vibrations in a Semiconductor Planar Phonon Cavity

Confinement of Acoustical Vibrations in a Semiconductor Planar Phonon Cavity

Phonon-Induced Optical Superlattice

Semiconductor superlattices: A tool for terahertz acoustics

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