Strain relaxation of pseudomorphic [formula omitted] heterostructures after hydrogen or helium ion implantation for virtual substrate fabrication

Abstract

Strain relaxed Si 1− x Ge x layers on Si(1 0 0) are used as virtual substrates for the growth of e.g. Si/Si 1− x Ge x quantum well structures. We investigated the effects of H + and He + ion implantation and subsequent annealing on pseudomorphic Si 1−x Ge x/ Si(1 0 0) heterostructures grown by molecular beam epitaxy (MBE). A narrow defect band is generated by ion implantation slightly underneath the interface inducing the formation of strain-relieving misfit dislocations (MDs) during subsequent thermal annealing. Using H + ion implantation, nearly complete strain relaxation of Si 1− x Ge x layers with Ge fractions up to 22 at.% was obtained at temperatures as low as 800°C and the samples appeared free of threading dislocations (TDs) within the SiGe layer to the limit of transmission electron microscopy (TEM) analysis. Efficient strain relaxation was demonstrated even for Si 1− x Ge x layers with Ge fractions up to 30 at.% using He + ion implantation. We have thus developed a method for producing high-quality, thin, relaxed Si 1− x Ge x films on Si(1 0 0) with TD densities well below 10 7 cm −2 by standard techniques as MBE and ion implantation. The heterostructures were analyzed using X-ray diffraction (XRD), Rutherford backscattering/channeling spectrometry and TEM. We propose a model of strain relaxation in which dislocations generated in conjunction with the formation of H or He filled overpressurized cavities glide to the interface where they form strain-relieving misfit segments. On the basis of this assumption, the conditions for efficient strain relaxation are discussed.