Ultra-long-lived coherent acoustic phonons in GaN single crystals

Wu, S.; Zhang, J; Belousov, Andrey; Karpiński, J.; Sobolewski, Roman

doi:10.1088/1742-6596/92/1/012021

Cited by 3 publications

(3 citation statements)

References 7 publications

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“…Very recently our group presented comprehensive studies on the inter-band electron transfer process in optically excited GaN single crystals [8]. We have also observed generation and propagation of very-long-lived coherent acoustic phonons (CAPs) [9] and developed a new model, which confirmed that in GaN crystals excited with femtosecond optical pulses with photon energies above the material E g , CAPs are generated due optically-induced electronic stress in the material and next propagate over macroscopic distances in a dispersionless manner without losing their coherence [10], [11].…”

Section: Introductionmentioning

confidence: 59%

Femtosecond pump-probe characterization of high-pressure grown Al x Ga 1-x N single crystals

et al. 2009

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We report our experimental studies on the time-resolved dynamics of conduction electrons in high quality Al x Ga 1-x N single crystals. The Al x Ga 1-x N synthesis with the Al content of up to 90% was performed using a solution growth technique in a high nitrogen pressure system, maintained for several days under the high (up to 15 kBar) gas pressure and at very high (up to 1800°C) temperatures. The resulting crystals were colorless (fully transparent to visible light) platelets up to ~1 mm 2 in size, and exhibited a hexagonal Würtzite structure. Our optical measurements were performed at room temperature, using a two-color (ultraviolet and near-infrared), femtosecond, pump-probe spectroscopy, by invoking a two-photon, volume absorption and scanning the normalized transient differential transmitivitty ( T/T) signal of the probe beam. The observed T/T signal was a superposition of a femtosecond, two-photon-absorption (TPA) correlation transient and a conventional optical pump-probe photoresponse signal with a rise time of ~1 ps and decay of ~75 ps. We have found that the TPA process was quite efficient with the absorption coefficient 0.337 cm/GW at 380 nm, and enabled us to directly determine that the optical bandgap of Al x Ga 1-x N (x = 0.86) was 5.81 +/-0.01 eV. The latter value is in the good agreement with the one deduced from the x-ray diffraction measurements.

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Section: Introductionmentioning

confidence: 59%

Femtosecond pump-probe characterization of high-pressure grown Al x Ga 1-x N single crystals

et al. 2009

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“…(iv) Phonon-phonon relaxation time, which is responsible for cooling due to heat transfer at the interfaces of materials, which is of the order of hundreds of picoseconds (Link & El-Sayed, 1999) and, in some cases, nanoseconds (Wu et al, 2007;Highland et al, 2007).…”

Section: Applicability Of Classical Heat-load Model At Nanoscalementioning

confidence: 99%

Radiation-induced melting in coherent X-ray diffractive imaging at the nanoscale

Ponomarenko¹,

Nikulin²,

Moser³

et al. 2011

J Synchrotron Radiat

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Coherent X-ray diffraction techniques play an increasingly significant role in the imaging of nanoscale structures, ranging from metallic and semiconductor to biological objects. In material science, X-rays are usually considered to be of a low-destructive nature, but under certain conditions they can cause significant radiation damage and heat loading on the samples. The qualitative literature data concerning the tolerance of nanostructured samples to synchrotron radiation in coherent diffraction imaging experiments are scarce. In this work the experimental evidence of a complete destruction of polymer and gold nanosamples by the synchrotron beam is reported in the case of imaging at 1-10 nm spatial resolution. Numerical simulations based on a heat-transfer model demonstrate the high sensitivity of temperature distribution in samples to macroscopic experimental parameters such as the conduction properties of materials, radiation heat transfer and convection. However, for realistic experimental conditions the calculated rates of temperature rise alone cannot explain the melting transitions observed in the nanosamples. Comparison of these results with the literature data allows a specific scenario of the sample destruction in each particular case to be presented, and a strategy for damage reduction to be proposed.

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“…The generation of transient THz signals (THz bursts) can be achieved by a variety of techniques, including ultrafast switching of photoconductive antennas and optical rectification in nonlinear crystals [3]. Technological innovation in photonics and nanoscience enable novel THz generation techniques, such as coherent excitation of acoustic waves or polar optical phonons, laser induced gas plasma, and carrier tunneling in coupled double-quantum-well structures [4][5][6][7]. However, optically excited photoconductive antennas are still the most efficient devices for THz radiation generation, reliably providing high-intensity and wide-spectral bandwidth signals.…”

Section: Introductionmentioning

confidence: 99%

Generation of THz transients by photoexcited single-crystal GaAs meso-structures

et al. 2013

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We report a sub-picosecond photoresponse and THz transient generation of GaAs single-crystal mesoscopic platelets excited by femtosecond optical pulses. Our structures were fabricated by a top-down technique, by patterning an epitaxial, 500-nm-thick GaAs film grown on top of an AlAs sacrificial layer and then transferring the resulting etched away 10 9 20-lm 2 platelets onto an MgO substrate using a micropipette. The freestanding GaAs devices, incorporated into an Au coplanar strip line, exhibited extremely low dark currents and *0.4 % detection efficiency at 10 V bias. The all-optical, pumpprobe carrier dynamics analysis showed that, for 800-nmwavelength excitation, the intrinsic relaxation of photocarriers featured a 310-fs-wide transient with a 290 fs fall time. We have also carried out a femtosecond, timeresolved electro-optic characterization of our devices and recorded along the transmission line the electrical transients as short as *600 fs, when the platelet was excited by a train of 100-fs-wide, 800-nm-wavelength optical laser pulses. The platelets have been also demonstrated to be very efficient generators of free-space propagating THz transients with the spectral bandwidth exceeding 2 THz. The presented performance of the epitaxial, freestanding GaAs meso-structured photodevices makes them uniquely suitable for THz-frequency optoelectronic applications, ranging from ultrafast photodetectors to THz-bandwidth optical-to-electrical transducers and photomixers.

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Ultra-long-lived coherent acoustic phonons in GaN single crystals

Cited by 3 publications

References 7 publications

Femtosecond pump-probe characterization of high-pressure grown Al x Ga 1-x N single crystals

Femtosecond pump-probe characterization of high-pressure grown Al x Ga 1-x N single crystals

Radiation-induced melting in coherent X-ray diffractive imaging at the nanoscale

Generation of THz transients by photoexcited single-crystal GaAs meso-structures

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