Si nanocrystal synthesis via double implantation and variable implantation

James M. Gaudet, The University of Western Ontario

Abstract

Silicon (Si) nanocrystals (nc) precipitated from silicon-implanted silicon oxide (SiO₂) are of interest as a novel light source for illumination, biomedical applications, optical computing, etc. They have some advantages over conventional III-V compound semiconductor nanocrystals produced by colloidal synthesis. They are compatible with Si/SiO₂ based semiconductor processing, are stable, non-toxic at point of synthesis and consumption, and their luminescence falls with the infrared transmission window of biological materials. Unfortunately, synthesis of Si-nc embedded SiO₂ is uneconomical and is not as amenable to precise control of the size distribution of nanocrystals as is the case for III-V compound colloidal nanocrystals.

The distribution of nanocrystals precipitated out of a sample is affected by the purity of the SiO₂ implantation target, the implantation temperature, the implanted Si⁺ dose and energy, the anneal temperature, the anneal ramp rate, total anneal time, and the use of secondary annealing in a passivating gas atmosphere.

Two studies were conducted within the scope of this thesis. The first concerned the enhancement of Si-nc precipitation by use of a double implant procedure to increase the vacancy concentration in the implanted region. The second involved the development of a combinatorial implantation and characterization procedure to allow many implantation doses to be synthesized at once, thereby more rapidly optimizing synthesis procedure. An exponential dose profile was implanted in thermal oxide and fused silica. Optical absorption profiles were measured for the implanted fused silica and photoluminescence profiles were made for both samples. It was determined that the implanted thermal oxide yielded Si-nc with a quantum confinement mechanism. Both samples also yielded luminescence from another, unspecified mechanism. By comparing the quantum confined luminescence from the thermal oxide in both studies, it was confirmed that the double implant procedure does yield enhanced Si-nc precipitation, even with a much lower concentration of excess Si.

Based on the literature review and experimental results, various recommendations are made for future work.