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Thesis Format

Integrated Article

Degree

Doctor of Philosophy

Program

Physics

Supervisor

Goncharova, Lyudmila V.

2nd Supervisor

Simpson, Peter J.

Affiliation

The University of British Columbia, Kelowna, BC, Canada

Co-Supervisor

Abstract

The advancement of semiconductor materials has played a crucial role in driving positive technological breakthroughs that impact humanity in numerous ways. The presence of defects significantly alters the physical properties of semiconductors, making their analysis essential in the fabrication of semiconductor devices. I presented a new method to quantify surface and near-surface defects in single crystal semiconductors. Epitaxially-grown silicon was measured by low energy electron diffraction (LEED) to obtain the surface Debye temperature (θD). The results showed the surface θD of bulk Si (001), 1.0 μm, and 0.6 μm Si on sapphire of 333 K, 299 K, and 260 K, respectively. Complementary measurements using Rutherford backscattering spectrometry (RBS) and positron annihilation spectroscopy (PAS) showed a correlation between the concentration of defects Nd and the change in the surface θD, expressed by the empirical relation θD = (365 ± 14) − (8.1 ± 1.5) × 10−13Nd for silicon. Arrays of SiGe quantum dots (QDs) ranging from 1.7 to 5.7 nm in diameter were fabricated using two methods: co-implantation of Si and Ge into an SiO2 matrix, and a hybrid method involving plasma-enhanced chemical vapor deposition (PECVD) of Si-rich SiOx deposition plus Ge implantation. Ion implantation conditions allowed incorporation of up to 8.0 peak Ge at.% and identical thermal procedures were used in both methods. SiGe QD arrays in both methods exhibited photoluminescence in the visible and near-infrared spectra, with emissions from 780 nm to about 1020 nm. Incorporation of Ge, confirmed by Raman spectroscopy, induced a shift towards higher wavelengths in the light emission. Time-resolved photoluminescence measurements indicated average-weighted lifetimes ranging from 34 μs to 220 μs, with a decreasing trend noted with increasing Ge concentrations. Experimentally observed differences in PL peak intensity and width for the two fabrication approaches can be connected to SiGe QD size distributions and matrix effects.

Summary for Lay Audience

Novel semiconductor materials and devices have been continuously changing our very-day life and society. Defects can affect semiconductor performance in many positive ways and some negative ways. This thesis investigates the relationship between defects in semiconductor crystals and the Debye temperature. Defects are defined as atomic level imperfections such as impurities or disorder in the crystalline structure. To illustrate, imagine a solid composed of billions of orderly cubes arranged side by side. We expect atoms to occupy the eight vertices of each cube. However, if one atom is located at the center of the cube while the other seven are at the vertices, we have what is referred to as a defect. The Debye temperature of a solid serves as a metric for gauging the extent of atomic jiggling and vibration within a material. It provides insights into the average energy of these minuscule particles and helps in comprehending their behavior when the material undergoes heating or cooling. Therefore, employing surface analysis to measure Debye temperature, and ion beam techniques to quantify the concentration of defects, I found that a higher defect concentration leads to a lower Debye temperature, sug- gesting that measurements of the Debye temperature can be used to estimate the concentration of defects.

I fabricated silicon-germanium quantum dots, which are nanometer-scale particles, embedded in a silicon oxide matrix. Light emission of these quantum dots is enhanced significantly compared to the bulk analogs. This is particularly relevant today, given that the primary hardware in cutting-edge technologies like AI and big data involves integrated optical circuits known as system-on-chip. Within these chips, various components, such as a CPU, memory, and sensors, coexist and communicate through metallic wires. Shifting their communication to light could lead to reduced power consumption and enhanced processing power. I explored how the light emission of these SiGe quantum dots correlates with the concentration of germanium. In the fabrication process, I discovered a more effective procedure to thermally process these samples to incorporate germanium into the quantum dots. Furthermore, I demonstrated that adjusting the amount of germanium allows us to modify the wavelength of the light emitted from the quantum dots.

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Creative Commons Attribution 4.0 License
This work is licensed under a Creative Commons Attribution 4.0 License.

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