Applications of Photoluminescence Microscopy for Probing Bulk Defects in Silicon

Global adoption of photovoltaics for power generation is expected to accelerate over the next decades due to increased concern regarding climate change and their reduced cost. However, to benefit the full potential of photovoltaic energy, their efficiency needs to be further increased. A key factor limiting silicon solar cell efficiency is the bulk carrier recombination. Despite the large number of studies investigating the recombination parameters of various defects causing bulk recombination, they are not fully understood. One of the main limiting factors lies in the abilities of conventional techniques to probe bulk defects. Therefore, further improvements may be achieved with development of new approaches to measure and parameterize the recombination activity of bulk defects. Bulk defects in silicon occur non-uniformly may be probed via the photoluminescence (PL) microscopy or μPL technique. The main advantages of this technique over existing methods to measure bulk defect recombination are the localised excitation and detection and the easy integration of hardware for variation of the excitation, detection, sample temperature and sample position. In this study, a custom PL microscopy setup is developed. The system is then used for investigation of radiative defect transitions using spectral PL. First, a study using numerical simulations of a novel bulk excitation method -- two-photon absorption time-resolved PL -- is presented. It is demonstrated that the method cannot be used to measure bulk lifetime for silicon wafers, due to the long diffusion length relative to the wafer thickness. However, a follow-up feasibility study accounting for actual experimental hardware indicates that the bulk lifetime in silicon bricks and ingots can be extracted using this method. Then, radiative transitions from bulk defects in silicon are investigated using spectral μPL combined with temperature- and light-intensity and spatially dependent techniques. A detailed analysis is de