Complex interface and growth analysis of single crystalline epi-Si(111)/Y2O3/ Pr2O3/Si(111) heterostructures: Strain engineering by oxide buffer control

摘要

Complex oxide heterostructures on Si gain in the field of engineered Si wafers increasing interest as flexible buffer systems for developing virtual Si substrates. Strain engineering of thin epitaxial Si thin films on insulating oxide buffers is of special interest to boost charge carrier mobility for Silicon-on-Insulator (SOI) technologies. The single crystalline Si(111)/Y _2O_3 (111)/Pr_2O_3 (111)/Si(111) heterostructure offers, in principle, the opportunity to grow strain-engineered epitaxial Si(111) layers, realizing compressed, fully relaxed, as well as tensile-strained Si films. This flexibility is based on a thickness-dependence of the Y2O3 lattice constant in the oxide bi-layer buffer: In theory, the Y_2O_3 buffer lattice constant on Pr _2O_3/Si(111) can change from pseudomorphism (bigger than Si) over the Si lattice constant towards a fully relaxed status (smaller than Si). By a detailed interface analysis, using TEM-EELS in combination with an in-situ RHEED-XPS study of the isomorphic Y_2O_3 growth on Pr_2O_3/Si(111), the physical origin of this Y _2O_3 buffer lattice constant variation is identified. It is possible to discriminate between the contributions from chemical mixing effects between the isomorphic oxides Y_2O_3 and Pr _2O_3 on the one hand and true misfit strain relaxation mechanisms in stoichiometric Y_2O_3 on the other hand.