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Abstract
Time-resolved photoluminescence technique for silicon material characterisation involves the use of a time-dependent monochromatic light excitation to generate excess minority carriers. The subsequent radiative recombination of charge carriers then releases photons which can be captured as time-dependent luminescence signals. Compared with traditional photoluminescence characterisation techniques, time-resolved photoluminescence requires fewer prior assumptions.
This thesis carries out theoretical studies of time-resolved photoluminescence from silicon bricks and wafers by establishing comprehensive one-dimensional models for the time- and depth-dependent excess minority carrier concentration, and proposing algorithms for separating the bulk and surface properties from the measured signals.
Specifically, for silicon bricks, analytical solutions have been obtained for time-resolved photoluminescence by solving the full continuity equation of excess minority carrier concentration, which takes into account the bulk minority carrier lifetime, surface recombination velocities as well as the charge carrier transport. The time-resolved decay of photoluminescence is then used to investigate the impact of surface properties on the effective minority carrier lifetime. In addition, two time-resolved decays with different excitation wavelengths are able to establish two relations to separate the bulk minority carrier lifetime and surface recombination velocities. Finally, the reliability of this lifetime separation algorithm is studied for certain signal-to-noise ratio conditions.
Similarly, for silicon wafers, numerical solutions have been obtained. Besides, in order to model the time-resolved photoluminescence under repetitive excitation conditions, a finite element analysis approach is used to improve the computation efficiency with its validity being verified. The impacts of bulk and surface properties have been studied and a method which minimises the discrepancies between the simulated signal and the measured signal by varying the bulk and surface property values is used to extract the bulk minority carrier lifetime and surface recombination velocities. Eventually, this separation algorithm is extended to injection level dependent parameter situation with a slight modification of the excitation source. By repeating this process, the injection level dependencies of the bulk minority carrier lifetime and surface recombination velocities of silicon wafers can be resolved.