Thermal stability of a reverse-graded SiGe buffer layer for growth of relaxed SiGe epitaxy

We have recently developed a novel reverse-graded (RG) buffer system, in which the Ge content decreases with distance from the Si interface. These thin (90 nm) RG layers are capable of supporting the growth of relaxed SiGe layers (85% relaxed) with defect densities as low as 10 ⁵ cm ². Good quality strained Si has also been successfully grown on these substrates. However, the thermal stability of this novel heterostructure has not been explored. In this paper, we establish, by high-resolution X-ray diffraction, Raman spectroscopy, atomic force microscopy, and transmission electron microscopy, that the heterostructure is stable up to 1000°C with no further strain relaxation in both the RG layer and strained Si layer. Hence, it is clear that this thin RG heterostructure is highly suitable as a buffer system for the growth of high-mobility strained Si or Ge devices.