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

This work studies the scattering of coherent acoustical phonons within the frequency range of 30-200GHz 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 10nm) 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.