Advanced optoelectronic devices via defect engineering

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Silicon nanoparticles show promise to enable efficient light emitting devices, for a variety of applications including communications, all-optical computing, and illumination. Silicon is a very poor emitter of light, however by creating structures with nanometer-scale dimensions we can foster behaviour not found in the bulk material, including efficient emission of light. I propose research which will advance our ability to make silicon nanoparticles, to integrate them into functioning optoelectronic devices, and to understand the underlying physics. Current trends in technology towards nanoscale devices motivates the development of techniques and instruments to probe matter at the atomic scale. Atomic scale defects can be detrimental to device performance, but can also be exploited in the formation of devices and nanostructures. For example, vacancy-type defects (missing atoms) play an important role in the creation of light-emitting silicon nanoparticles, due to their action as a vehicle for silicon diffusion, which is essential to the process of precipitation that forms the nanoparticles. The proposed research will make use of the newly funded McMaster Intense Positron Beam Facility (MIPBF), which will generate intense beams of positrons, the antimatter counterpart of the electron, at the McMaster Nuclear Reactor. We will develop new techniques to probe defects in materials, to study issues such as (1) Grain boundary diffusion of impurities - solar cells and thin film transistors can be made from polycrystalline silicon - silicon that is made of many small grains. The boundaries between the grains can act as "highways" for the transport of impurities, and this can be detrimental to device performance and longevity. Diffusion of impurities along grain boundaries is a subject of growing importance, and I will develop a further understanding of it using the MIPBF. (2) Profiling of defects in ultrathin layers - the next generation of semiconductor devices like computer chips requires layers of material of the order of 10 nanometres in thickness, and this raises new materials challenges, including how to measure the properties of such thin films. I will develop advanced positron annihilation techniques to study these very small structures.