Recombination in light-pulse excited silicon at medium-high carrier concentration levels

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Abstract
Recombination in silicon has been studied by exciting gold on n_type silicon surface-barrier diodes. The excitation was short light pulses from a superradiant laser and the diodes were reverse biased at more than the depletion voltage. The energy in the light pulse was monitored and a comparison was made with the measured charge in the resulting current pulse in the diode. In this way recombination losses could be determined. At high light intensities (1010−6×1011 photons/cm2 in a 1-nsec excitation pulse) superlinear recombination of carriers is observed, causing the collected charge to decrease by up to 50% of the value expected from the observed quantum detection efficiency of approximately unity observed at lower levels. This is attributed to recombination near the surface at the high carrier densities reached, both during the light pulse and during the charge reservoir time tA (the time for extraction of space-charge-limited current from the cathode). This causes the recombined charge to increase with both light intensity and tA. The observed recombination may be of practical importance when operating semiconductor detectors at high light levels or with heavily ionizing nuclear particles.