Abstract
An analysis of devices with drift fields formed by an impurity gradient is carried out allowing for lifetime and mobility variations with impurity concentration. In the case of silicon n-on-p photovoltaic solar cells, a field width of about twice the diffusion length of the minority carriers maximizes the collection efficiency. For lifetimes longer than one microsecond the optimum field width is about 25 µm, a value governed by the absorption characteristics rather than the diffusion length. In most cases, increasing the concentration ratio above 3 orders of magnitude is of little or no assistance in improving the collection efficiency. It is also shown that if the constant relating lifetime to high energy-particle flux is a strong function of impurity concentration, there is little advantage in using drift-field solar cell structures to enhance radiation resistance.

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