We investigate the heteroepitaxial Si0.5Ge0.5 quantum dot site-selection on a patterned Si(001) substrate by continuously varying the underlying substrate pattern morphology from pit-in-terrace to quasi-sinusoidal. The pit-in-terrace morphology leads to well-ordered quantum dots centered in the pits over a wide range of pattern wavelengths. However, for quasi-sinusoidal morphology, when the pattern wavelength is twice the intrinsic lengthscale, quantum dots suddenly bifurcate and shift to form in every saddle point, with high uniformity in size and site occupancy. We compare our results with existing models of quantum dot formation on patterned surfaces.

Spectral linewidths are used to assess a variety of physical properties, even as spectral overlap makes quantitative extraction difficult owing to uncertainty. Uncertainty, in turn, can be minimized with the choice of appropriate experimental conditions used in spectral collection. In response, we assess the experimental factors dictating uncertainty in the quantification of linewidth from a Raman experiment highlighting the comparative influence of (1) spectral resolution, (2) signal to noise, and (3) relative peak intensity (RPI) of the overlapping peaks. Practically, Raman spectra of SiGe thin films were obtained experimentally and simulated virtually under a variety of conditions. RPI is found to be the most impactful parameter in specifying linewidth followed by the spectral resolution and signal to noise. While developed for Raman experiments, the results are generally applicable to spectroscopic linewidth studies illuminating the experimental trade-offs inherent in quantification.

Chemical ordering in semiconductor alloys could modify thermal and electronic transport, with potential benefits to thermoelectric properties. Here, metastable ordering that occurs during heteroepitaxial growth of Si1−xGex thin film alloys on Si(001) and Ge(001) substrates is investigated. A parametric study was performed to study how strain, surface roughness, and growth parameters affect the order parameter during the alloy growth. The order parameter for the alloy films was carefully quantified using x-ray diffraction, taking into account an often-overlooked issue associated with the presence of multiple spatial variants associated with ordering along equivalent 〈111〉 directions. Optimal ordering was observed in the films having the smoothest surfaces. Extended strain relaxation is suggested to reduce the apparent order through creation of anti-phase boundaries. Ordering surprisingly persists even when the film surface extensively roughens to form {105} facets. Growth on deliberately miscut Si(001) surfaces does not affect the volume-averaged order parameter but does impact the relative volume fractions of the equivalent ordered variants in a manner consistent with geometrically necessary changes in step populations. These results provide somewhat self-contradictory implications for the role of step edges in controlling the ordering process, indicating that our understanding is still incomplete.

This dissertation describes investigations of structural ordering in the Si-Ge material system from nano-to-meso scale in order to modify electronic and thermal transport properties for potential improvement in thermoelectric or nanoelectronics applications.We first present the synthesis and characterization of mono-layer scale chemically ordered Si1-xGex alloys. Here, metastable ordering to an L11-like structure, occurring during

Ordered arrays of semiconductor quantum dots may provide new electronic, optical, or thermoelectric functionalities. In this work, we create ordered two-dimensional arrays of Si-Ge quantum dots by heteroepitaxial growth on Si (001) with pre-patterned pits. Instead of growing the dots directly at elevated temperatures, we first grow conformal alloy layers and then use post-growth annealing to promote directed self-assembly. Annealing provides monodisperse size distributions with excellent control over the quantum dot (QD) mean size and shape. Similar to QD formation during growth, intermixing with substrate Si occurs, despite the conformal layer, due to the presence of the pattern topography itself.