Generation and Propagation of Superhigh-Frequency Bulk Acoustic Waves in GaAs

Abstract

Coherent super-high-frequency (SHF) vibrations provide an excellent tool for the modulation and control of excitations in semiconductors. Here, we investigate the piezoelectric generation and propagation of longitudinal bulk acoustic waves (LBAWs) with frequencies up to 20 GHz in GaAs crystals using bulk acoustic wave resonators (BAWRs) based on piezoelectric thin ZnO films. We show that the electro-acoustic conversion efficiency of the BAWRs depends sensitively on the sputtering conditions of the ZnO films. The BAWRs were then used for the study of the propagation properties of the LBAWs in GaAs in the frequency and temperature ranges from 1 to 20 GHz and 10 and 300 K, respectively, which have so far not been experimentally accessed. We found that the acoustic absorption of GaAs in the temperature range from 80 K to 300 K is dominated by scattering with thermal phonons. At lower temperatures, in contrast, the acoustic absorption saturates at a frequency-dependent value. Experiments carried out with different propagation lengths indicate that the saturation is associated with losses during reflections at the sample boundaries. We also demonstrate devices with high quality factor fabricated on top of acoustic Bragg-reflectors. The results presented here prove the feasibility of high-quality acoustic resonators embedding GaAsbased nanostructures, thus opening the way for the modulation and control of their properties by electrically excited SHF LBAWs. I. arXiv:1907.09787v2 [cond-mat.mtrl-sci] 4 Sep 2019 FIG. 2. (a) Calculated dependence of the |s11| 2 scattering parameter (corresponding to the rf-reflection coefficient) for a BAWR on a GaAs (001) wafer consisting of a dZnO = 440 nm-thick ZnO layer sandwiched between bottom and top metal contacts formed by a 40 nm Au film and a 10 nm/30 nm/10 nm Ti/Al/Ti layer stack, respectively. The active area of the resonator is equal to 1960 µm 2 . (b) Dependence of the resonance frequency on dZnO: the joined full square symbols are finite element method calculations, and the open circle symbols are experimental values. The dashed line reproduces the approximation for the resonance frequency given by Eq. (1). The blue open square at fR ∼ = 5 GHz corresponds to the device simulated in (a) and (c). (c) Cross-section map of the amplitude of the displacement field of the BAWR in (a) at the resonance frequency. The calculation domain was surrounded by perfectly matched layers (PMLs) to reduce acoustic reflections from the sample boundaries.

Protected Long-Distance Guiding of Hypersound Underneath a Nanocorrugated Surface

“…Recently such generation of hypersound with frequency up to 20 GHz has been demonstrated in Ref. [41] with piezoelectric ZnO transducers; application of such electrical technique to the corrugated surface could lead for wider applications of subsurface hypersound. 2𝜎 2 ), where r is the distance from the center of the spot and  =1 mm is the spot radius at…”

Electrically driven exciton-polariton optomechanics at super high frequencies

“…The BAWs were excited by bulk acoustic wave resonators (BAWRs) [22,32] deposited on the sample surface, as illustrated schematically in Fig. 1(a).…”

“…This platform profits, on one side, from the long effective lifetimes of phonons confined in the MC, which less susceptible to adverse surface degradation of the quality factor and yield huge Qf products exceeding 10 14 Hz. [1,22,27] On the other side, it exploits the high sensitivity of the excitonic resonances to confined strain field, which enables the modulation of the polaritonic energies over a range exceeding the light-matter Rabi coupling strength and reaching effective optomechanical couplings exceeding g eff ∼ 20 THz/nm. As a prospect, the results open the way to resonant optomechanics in the non-adiabatic regime, side-band limited, using polariton condensates with spectral linewidths (< 10 µeV) [28]) considerably smaller than the ones for the sub-condensation regime reported here.…”

“…The thin curves are the corresponding finite-element calculations of the s 11 response for varying thicknesses d ZnO of the ZnO layer, which accurately reproduce the measured response for nominal thickness d ZnO = 240nm (thick line). [22,23] While the MC mode is essentially insensitive to d ZnO , the S mode shift towards lower frequencies with decreasing d ZnO . This behavior arises from the fact that S-mode is confined between the upper aoDBR and the BAWR surface, while the MC mode is concentrated in-between aoDBRs, as illustrated by the calculated mode profiles of Figs.…”

“…Here, we introduce a platform for electrically driven MP optomechanics in the SHF region (3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20) based on phonon generation and detection using highfrequency BAW resonators (BAWRs). The BAWR enables acoustic echo spectroscopy with a very high (over 90 dB) dynamic range [22]. The latter is important to unveil the distribution of the acoustic field within the samples, which results from the resonant coupling of BAWs modes confined in three coupled acoustic cavities: the main one within the MC spacer, a surface cavity between the upper and lower distributed Bragg reflectors (DBRs) and a bulk cavity formed by the front and back surfaces of the wafer.…”