Strain relaxation of pseudomorphic Si1-xGex/Si(100) heterostructures afterhydrogen or helium ion implantation for virtual substrate fabrication

Strain relaxed Si1-xGex layers on Si (100) are used as virtual substrates f or the growth of e.g. Si/Si1-xGex quantum well structures. We investigated the effects of H+ and He+ ion implantation and subsequent annealing on pseu domorphic Si1-xGex/Si(100) heterostructures grown by molecular beam epitaxy (MBE). A narrow defect band is generated by ion implantation slightly unde rneath the interface inducing the formation of strain-relieving misfit disl ocations (MDs) during subsequent thermal annealing. Using H+ ion implantati on, nearly complete strain relaxation of Si1-xGex layers with Ge fractions up to 22 at.% was obtained at temperatures as low as 800 degreesC and the s amples 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 Si1-xGex layers with Ge fractio ns up to 30 at.% using He+ ion implantation. We have thus developed a metho d for producing high-quality, thin, relaxed Si1-xGex films on Si(100) 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 (X RD), 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 o f this assumption, the conditions for efficient strain relaxation are discu ssed. (C) 2001 Elsevier Science B.V. All rights reserved.