Picosecond ultrasonic measurements of attenuation of longitudinal acoustic phonons in silicon

Abstract

We report ultrafast optical measurements of the attenuation of 50 and 100 GHz longitudinal acoustic-phonon pulses in Si. Picosecond acoustic measurements were made at temperatures 50Ͻ T Ͻ 300 K on thinned ͑50-m-thick͒ wafers. The measured phonon lifetimes at 300 K, Ϸ5 -7 ns, are an order of magnitude less than expected based on three-phonon scattering rates derived from thermal conductivity data. We find instead that relaxational damping is the dominant mechanism in this frequency and temperature range. This attenuation sets an intrinsic limit on the quality factor of nanomechanical resonators that operate near room temperature.

Study of confined coherent acoustic phonon modes in a free-standing cubic GaN membrane by femtosecond spectroscopy

“…Time-resolved pump-probe spectroscopy has been applied to study ultrafast carrier dynamics and phononic properties of various semiconductors, such as GaN, [1][2][3][4] GaAs, [5][6][7] and Si. [8][9][10][11] Among these, GaN is of great importance in optoelectronic and short-wavelength devices because of its widebandgap. [12][13][14] GaN has two crystal structures: wurtzite (hexagonal) and zinc-blende (cubic).…”

Coherent Control of GHz Resonant Modes by an Integrated Acoustic Etalon

“…In conclusion, we have shown how a compliant supporting layer can allow multiple harmonics to persist simultaneously in a supported membrane resonator, the dynamics of which differ fundamentally from the echo behavior typically observed when metal transducers are placed on noncompliant substrates [8,16,19]. Because the compliant layer forms part of the acoustic cavity, …”

“…The acoustic dynamics of supported thin films under ultrafast laser excitation have been the subject of several recent studies [8,[16][17][18][19][20]. The absorption of laser pulses by a metal transducer in contact with a relatively hard material such as silicon or sapphire is known to lead to a train of acoustic echoes (rather than excited vibrational modes of the film) if the metal thickness is much larger than the optical penetration depth [8,16].…”

Picosecond Acoustics in Single Quantum Wells of Cubic GaN/(Al,Ga)N

“…As a result, an acoustic pulse is launched into the Si substrate, which propagates towards the c-GaN QW on the sample's front side with the sound velocity v [12]. To prevent a strong attenuation of the acoustic pulse during the Si=SiC substrate transit, the sample is placed into a flow cryostat and cooled down to 40 K [13]. The input acoustic pulse is depicted in Fig.…”