The growth of high-quality SiGe films with an intermediate Si layer

The growth of high-quality relaxed SiGe epilayer has been achieved by introducing an intermediate Si layer in the SiGe film. It was found that intermediate Si in the SiGe film changed the mechanism of strain relaxation during the growth so that the shallow pits related to strain relief on the surface were suppressed. Such a SiGe/Si/SiGe heterostructure has a threading dislocation density of 8.9 × 10⁵ cm^-2 and a root mean square roughness of 3 nm. The intermediate Si layer was also demonstrated to act as effective nucleation site for dislocation loops to relax the mismatch strain. A mechanism of strain relaxation for this intermediate Si layer is proposed. Compared with the conventional compositionally graded buffer layer, it has the advantages of having thinner buffer layer for required degree of relaxation, smoother surface, and maintaining the threading dislocation density at the same level.