Determination of bulk lifetime and surface recombination velocity of silicon ingots from dynamic photoluminescence

This paper elaborates upon the theory of self-consistent minority carrier bulk lifetime measurements of silicon ingots via time-modulated photoluminescence and presents an experimental proof of concept. For silicon ingots, the solution of the continuity equation at harmonic time modulation of excess carrier generation is shown to generally reveal a remarkably pronounced contrast with respect to minority carrier bulk lifetime. We combine our dynamic self-consistent approach with an analysis of surface recombination velocity from photoluminescence intensity ratios upon irradiation with different laser wavelengths. This combined analysis enables an accurate simultaneous determination of bulk lifetime and surface recombination velocity. For sufficiently high or accurately known ingot surface recombination velocities, this approach could likewise be used for an accurate determination of the minority carrier diffusion coefficient and of minority carrier mobility in novel silicon materials

Large historical changes of fossil-fuel black carbon aerosols

Anthropogenic emissions of fine black carbon (BC) particles, the principal light-absorbing atmospheric aerosol, have varied during the past century in response to changes of fossil-fuel utilization, technology developments, and emission controls. We estimate historical trends of fossil-fuel BC emissions in six regions that represent about two-thirds of present day emissions and extrapolate these to global emissions from 1875 onward. Qualitative features in these trends show rapid increase in the latter part of the 1800s, the leveling off in the first half of the 1900s, and the re-acceleration in the past 50 years as China and India developed. We find that historical changes of fuel utilization have caused large temporal change in aerosol absorption, and thus substantial change of aerosol single scatter albedo in some regions, which suggests that BC may have contributed to global temperature changes in the past century. This implies that the BC history needs to be represented realistically in climate change assessments