Dear Ali,

Silvaco is a device simulator based on solving the semiconductor equations governing the conduction in the regions of the device. These equations are differential equations requiring the boundary and initial conditions. The solving method is numerical based on finite element or finite difference method. Since the dynamic range of the numbers are limited in digital computer, therefore every parameter must be limited in its values to avoid overflow. From the conceptual point of view infinity can not be represented in the numerical computations. Instead, you can let the surface recombination velocity be as high as its highest physical value around 10^7 cm/s.

Physically, the surface recombination velocity is not infinite. 

here is an alternative of assuming infinite surface recombination velocity. You can assume that the excess minority charge density is equal to zero.

wish you success

Dear Abdelhalim, I thank you for your helpful answer.