Effect of surface recombination on the decay of excess minority carriers in semiconductors induced by finely focused picosecond pulsed laser beams

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Abstract
A study is carried out of the effect of surface recombination on the decay of the excess minority carrier population induced in a semiconductor sample by a very short pulse of a finely focused laser beam. An expression is obtained for this decay in a substantially simplified form, which can be readily computed numerically. Some sample calculations are presented, which show that, in agreement with previous experimental observations, this effect is important only for the initial part of the decay and only for large values of surface recombination velocity (>104 cm/sec) and absorption coefficient. If the initial fast portion of the decay is neglected, the minority carrier lifetime can be determined fairly accurately from the average slope of the remaining part of the decay, the resultant error being typically up to 15%.