Influence of recombination in p-n junction space-charge region of photocurrent under parallel illumination.

In a previous paper (Constantinescu et al. 1973), which shall in this paper be referred to as I, photovoltaic effects in p-n junctions under parallel illumination were discussed and mathematical expressions for the short-circuit current and open-circuit voltage were derived. One of the assumptions used there was, that all minority carriers generated outside the depletion region, which succeeded in reaching by diffusion the depletion (space-charge) region boundary, were swept away by the junction field and did not recombine in the 'thin' depletion layer, thus contributing to the photocurrent. However, as we shall see below, recombination of minority carriers after having reached the space-charge region, cannot always be neglected. For normally illuminated p-n heterojunctions this very situation was considered by Kagan and Liubashevskaia (1970), who found expressions for the short-circuit current in the presence of recombination in the space-charge region. In order to do the same for parallel illumination we shall again write the two-dimensional continuity equations, one for the neutral region and the other for the space-charge region of one side of the junction, for instance the n-type side (see I). Multiple line equation(s) cannot be represented in ASCII text (1) and Multiple line equation(s) cannot be represented in ASCII text (2) where <Dgr>p, D<SUBp> and T<SUBp> are the non-equilibrium (excess) minority carrier densities, diffusion coefficients and lifetimes, respectively, u<SUBp>, is the drift velocity of holes in the junction field, <agr> the absorption coefficient, <eegr> the quantum efficiency and F<SUB0> the density of the incident photon flux. The symbols referring to the space-charge region are noted by an asterisk. [ABSTRACT FROM AUTHOR]