Modeling of Minority -Carrier Surface Recombination Velocity at Low-High Junction of

Modeling of recombination velocity of minority carriers at the p-p+ low-high junction end of the p-base region of n+-p-p+ silicon diodes has been carried out by taking the minority-carrier recombi- nation effects in the space-charge region (SCR) of the low-high (I-h) junction into account. Solving Poisson's equation in the SCR numeri- cally, it has been revealed that the SCR is composed of an accumula- tion layer on the p side and a depletion layer on the p+ side. Generally, the depletion layer is very thin as compared with the accumulation layer and the built-in potential across the depletion layer never exceeds the thermal voltage, i.e., kT/q. Further, the minority-carrier recom- bination in this layer is also insignificant. For most I-h junction-based silicon devices, in practice, the minority-carrier recombination in the accumulation layer controls the value of the effective minority-carrier recombination velocity (&) at the back surface of the p-base region and the influence of the recombination in the heavily doped p+ region is less significant. A new expression for the Se, has been derived in terms of material parameters (such as the doping concentration, mi- nority-carrier lifetime, and diffusion coefficient of the two regions) which is in excellent agreement with the experimentally measured val- ues of back surface recombination velocity for nf-p-p+ and p+-n-n+ solar cells reported in literature.

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