Date of Award
Doctor of Philosophy
Prof. Peter Simpson
This thesis describes experimental and theoretical research aimed at under standing and manipulating the growth and optical characteristics of silicon nanocrys tals (Si-nc). Si-nç were grown by implanting silicon ions into SÌO2 and annealing to promote the nanocrystal growth by precipitation and Ostwald ripening. This nano material system has the potential for fabricating a silicon-based light emitter, and possibly a silicon laser. A silicon-based light emitter is the key component missing for complete integration of silicon photonic devices on microprocessors.
Samples were prepared with various doses of implanted silicon, annealed to various temperatures and times, and studied by photoluminescence (PL), cathodo luminescence (CL), transmission electron microscopy (TEM), positron annihilation spectroscopy (PAS), Rutherford backscattering spectroscopy (RBS) and ellipsom- etry. It was determined from the depth profile of Si-nc obtained by TEM that vacancy-type defects introduced by implantation play a critical role in the Si-nc growth. Consequently, a double implant experiment at 450 keV and 90 keV was designed to increase the vacancy-type defect concentration in the region of the 90 keV implant, and resulted in increased PL emission intensity. This knowledge of the growth mechanism is beneficial for optimizing the light emission of Si-nc, while minimizing production costs and resources.
A simple theoretical model to predict the spectrum of light emission from the dimensions of Si-nc using a one-dimensional finite square well was constructed.
The model reasonably predicted the PL emission spectrum for our Si-nc and for those published by other authors. Using the model the optical efficiency of the nanocrystals was determined and revealed a possible quasi-direct band gap transition predicted for nanostructured materials. The simple emission model provides a tool to understand the changes occurring to the Si-nc system through PL measurements.
Finally the PL and CL of Si-nc are discussed in detail. The knowledge obtained on the growth and optical properties of Si-nc was applied to explain the increase in PL intensity with implantation dose, and the eventual decrease in intensity at very high doses. The CL emission was at a dramatically different wavelength than the PL and was determined to be caused by defects at the surface of the Si-nc.
Mokry, Christopher Ryan, "GROWTH AND CHARACTERIZATION OF LIGHT-EMITTING SILICON NANOCRYSTALS" (2009). Digitized Theses. 4160.