Control of strain status in SiGe thin film by epitaxial growth on Si with buried porous layer

Abstract

Single crystalline Si with buried porous layers was utilized as a substrate for the epitaxy of 100-nm-thick Si0.73Ge0.27. Raman spectroscopy revealed that the strain status in SiGe systematically changes according to the variation in the porosity of the substrate and that the strain relaxation in SiGe was found to proceed with increasing porosity. Furthermore, Si was found to be tensilely strained to reduce the compressive strain in SiGe. These results suggest that the appropriate design of the porosity and the thickness of the thin Si layer on the buried porous layer offers an alternative way to control strain status in SiGe.

TEM and STEM Observations of a Flat Continuous Silicon-Germanium Thin Film Epitaxially Grown on Porous Silicon

“…This suggests that the Si 0.73 Ge 0.27 film on the Si (100) wafer was strained. This result agrees with the fact that Si 0.73 Ge 0.27 is strained on a Si wafer, as we previously determined by Raman spectroscopy [24]. Figure 2 shows a cross-sectional HAADF image of Si 0.73 Ge 0.27 /20%-porosity porous Si.…”

“…It is clear that the origin of the Si 0.73 Ge 0.27 relaxation in this specimen is not the effect of dislocations. The TEM results of this study and the results of our previous analysis by Raman spectroscopy confirmed that the SiGe relaxation is due to the strain of the porous Si layer [24].…”

“…Therefore, we confirmed that the defect density of Si 0.73 Ge 0.27 /20%-porosity porous Si is quite low and similar to that of the strained Si 0.73 Ge 0.27 /Si (100) shown in Figure 1. We emphasize that Si 0.73 Ge 0.27 / 20%-porosity porous Si exhibited a 10% relaxation ratio [24]. It is clear that the origin of the Si 0.73 Ge 0.27 relaxation in this specimen is not the effect of dislocations.…”

“…We previously reported the results of the Raman spectroscopy of the relaxed SiGe on porous Si [24]. We showed that porous Si is strained by a Si 0.73 Ge 0.27 film.…”

“…Our group evaluated the elastic strains of both SiGe and porous Si layers using Raman spectroscopy and demonstrated that porous Si was strained and that SiGe had a lower strain than SiGe on bulk Si [24]. However, we did not confirm the crystallinity of the specimens at this stage.…”