Tensile strained Ge quantum wells on Si substrate: Post-growth annealing versus low temperature re-growth

• Published in: Materials science & engineering. B, Solid-state materials for advanced technology Solid-state materials for advanced technology, 2012-06, Vol.177 (10), p.696-699
• Main Authors: Süess, M.J., Carroll, L., Sigg, H., Diaz, A., Chrastina, D., Isella, G., Müller, E., Spolenak, R.
• Format: Article
• Language: English
• Subjects: Annealing; CMOS; Germanium; Multiple quantum well; Quantum wells; Raman spectroscopy; Silicon substrates; Silicon–germanium; Stacks; Strain; Tensile strain
• ISSN: 0921-5107; 1873-4944
• DOI: 10.1016/j.mseb.2011.10.009

We investigate tensile strained Ge/Si1−xGex (x=0.87) multiple quantum wells (MQW) on a Ge virtual substrate abruptly grown on Si for integration in CMOS technology. Two schemes are discussed – Scheme A in situ growth of the MQW stack combined with post-growth rapid thermal annealing (RTA) and Scheme B re-growth of the MQW stack on an RTA strain optimized Ge-VS. Samples are characterized by Raman spectroscopy, X-ray diffraction (XRD), scanning transmission electron microscopy, Brewster transmission and photo-reflectance spectroscopy. The strain in the as-grown virtual substrate of Scheme A, measured with Raman spectroscopy and XRD, increases from 0.17% to 0.24% after RTA to 850°C. XRD reveals an activated inter-diffusion of the MQWs and, at the highest temperatures (TRTA>750°C), a structural relaxation. The MQWs of Scheme B appear to be of inferior quality. The inter-band transitions in this material are comparatively blue shifted and broad, which is attributed to relaxation induced dislocations at the interface between the virtual substrate and the multiple quantum wells.