Vibrational properties of Si/Ge superlattices: Theory and in-plane Raman scattering experiments

• Published in: Solid-state electronics Vol. 37; no. 4; pp. 757 - 760
• Main Authors: Schorer, R., Abstreiter, G., de Gironcoli, S., Molinari, E., Kibbel, H., Kasper, E.
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Oxford Elsevier Ltd 1994; Elsevier Science
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Electronic structure and electrical properties of surfaces, interfaces, thin films and low-dimensional structures; Exact sciences and technology; Physics; Optical phonons; Germanium; Silicon; Experimental study; Raman scattering; Superlattices
• ISSN: 0038-1101; 1879-2405
• DOI: 10.1016/0038-1101(94)90293-3

Phonons in short-period (001)-Si n Ge n Superlattices (SL's) have been studied both theoretically, by a first principles approach including strain and interface intermixing, and experimentally by micro-Raman spectroscopy where in-plane scattering geometries allow the observation of both longitudinal (L) and transverse (T) modes. Experimental data are found to deviate considerably from theoretical predictions for SL's with ideally sharp interfaces, both in frequency of higher-order confined Si-like modes and in the polarization dependence of the SiGe-like “interface” peak (lineshape and L-T splitting). Supercell calculations representing interface intermixing within a simple model by 2–3 monolayers of SiGe alloy at the interfaces are found to reproduce these major experimental findings. Measurements of Raman resonance profiles of various SL phonon modes strongly confirm their calculated different spatial localization.