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

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.