Potentialities and basic principles of controlling the plastic relaxation of GeSi/Si and Ge/Si films with stepwise variation in the composition

GeSi/Si heterostructures consisting of a plastically relaxed layer that includes various fractions of Ge and which is grown on Si (001) span the values of the lattice parameter from equal to that in silicon to equal to that in germanium. The corresponding substrates are conventionally referred to as artificial. A number of methods exist for growing high-quality GeSi layers with as large as 100% of Ge on Si (001) substrates through an intermediate GeSi layer with a varying composition. However, it is desirable in a number of cases to have ultrathin (<1 μm) GeSi and Ge layers directly on the Si (001) substrate for practical applications. The results of new methods such as the use of a buffer Si layer grown at a comparatively low temperature (300-400 deg. C) in plastic relaxation of the GeSi/Si(001) heterostructures and also the use of surfactants (antimony and hydrogen) are analyzed. The examples of artificial introduction of centers for origination of misfit dislocations as an alternative to their introduction from the rough surface are considered. It can be concluded that, in order to expand the range of potentialities of growing perfect plastically relaxed GeSi (001) films, it is necessary to (i) make it possible to form in a controlled manner the centers for origination of the misfit dislocations and (ii) retard or completely suppress the transition of the growth mechanism from two-to three-dimensional in order to prevent the formation of additional misfit dislocations from the surface of the stressed film and, correspondingly, additional threading dislocations