Acoustic properties of strained SiGe/Si layers in the sub-terahertz frequency range

Abstract

This work studies the scattering of coherent acoustical phonons within the frequency range of 30−200 GHz in strained SiGe/Si heterostructures with uniform SiGe layers and layers where the initial stage of self-organized islands formation was observed. Coherent phonon pulses reflected by single SiGe layers were detected, and phonon interference in the systems composed of two thin (approximately 10 nm) SiGe layers was observed. Acoustical properties were determined for single SiGe layers, and lateral acoustical inhomogeneity of the layers was estimated in the subterahertz frequency range. The results show that within the range of germanium content of 10%−32% acoustical properties of an approximately 10-nm SiGe layer are insensitive to internal strains governed by lattice mismatch and non-uniformities caused by initial stage of Stranski–Krastanov growth. The sound velocity and wave impedance of SiGe layers can be determined within 5% error, using the corresponding parameters of relaxed SiGe solid solutions with the same germanium content.

3D Hypersound Microscopy of van der Waals Heterostructures

“…Acoustical imaging is well developed for standard semiconducting heterostructures . Thin layered materials and VdW heterostructures remain insufficiently explored.…”

“…To model the responses of the structures, the strain pulse excitation and propagation through a sequence of the layers on semi-infinite substrate were calculated as in ref . Then, the optical response of the structure was obtained analogous to that in ref .…”

“…16 Acoustical imaging is well developed for standard semiconducting heterostructures. 17 Thin layered materials and VdW heterostructures remain insufficiently explored. In refs 18−22, several picoacoustical approaches were first applied to thin flakes and VdW heterostructures.…”

“…The magenta curve in Figure 1a (right panel) shows a simulated spectrum of the optical response that assumes all Al film and laser pulse parameters are known; 17 the Al thickness (about 30 nm), rigidity of the interface (indicated in Table 1), and viscoelastic hypersound damping are adjustable parameters. The modeled Al thickness (30 nm) agrees well with the value of 35 nm measured by the quartz thickness monitor during the evaporation.…”

Hypersound tomography of graphitized layers buried into diamond matrix

“…The most suitable nondestructive method for studying acoustic properties is picosecond ultrasonics, which makes it possible to register acoustic vibrations of nanostructures with high lateral (∼1 µm) resolution. For example, in [13] this method was used to study the change in the bonding of the Au/Si interface after ion implantation; in [14] , [15] the elastic interaction at the interfaces of Van der Waals heterostructures was studied; and the acoustic properties of SiGe nanolayers were studied in [16] .…”