Carbon incorporation pathways and lattice site distributions in silicon carbide/silicon(001) and germanium carbide/germanium(001) alloys grown by molecular beam epitaxy.

摘要

In this research, C lattice site distributions in Si_1−yC _y/Si(001) and Ge_1−yC_y/Ge(001) layers grown by molecular beam epitaxy (MBE) were determined in order to develop an understanding of C incorporation pathways as a function of layer deposition conditions.; Fully-coherent Si_1−yC_y alloy layers were grown on Si(001) at temperatures T_s of 380 to 680°C with C fractions y ≤ 0.026. Si_1−yC_y(001) layers deposited at T_s 580°C are highly perfect single-crystals as judged by plan-view and cross-sectional transmission electron microscopy (TEM and XTEM) with all C, irrespective of alloy composition, incorporated in substitutional lattice sites as determined from strain and Raman spectroscopy measurements.; Epitaxial metastable Ge_1−yC_y(001) alloy layers with y ≤ 0.045 were grown on Ge(001) by MBE at T_s = 200–400°C. Using calculated strain coefficients and measured layer strains obtained from high-resolution reciprocal lattice maps (HR-RLMs), I determined C lattice site distributions as a function of T_s and the total C concentration y. HR-RLMs show that as-deposited alloys are fully-coherent with their substrates. All films contain C in both substitutional sites, giving rise to tensile strain, and nanocluster sites which induce negligible lattice strain.; Annealing Ge_1−yC_y(001) layers at 550°C leads to a significant decrease in ξ_sub and, hence, in tensile strain while 650°C annealed layers are strain- and defect-free as all substitutional C migrates to lower-energy nanocluster sites.; The key results of this research can be summarized as follows: (1) In Si_1−yC_y/Si(001), alloys, I find that all C incorporates in substitutional sites at T_s 580°C with y ≤ 0.026. At T_s ≥ 580°C, increasing y and T_s leads to increase in the fraction of dicarbon complexes and the formation of periodic bulk planar structures consisting of ordered Si₄C layers which form as a result of C surface segregation. (2) In contrast to Si_1−yC _y/Si(001), I find that irrespective of y and T_s values, complete substitutional C incorporation in Ge_1−yC_y/Ge(001) is not possible. A fraction of the total C concentration is always incorporated in nanoclusters. Increasing y and/or T_s leads to an increase in the fraction of C in nanoclusters due to a higher C-C encounter probability at the growth surface. (Abstract shortened by UMI.)