This research intends to investigate a mathematical model for In-doped silicon (n) structure, and calculate the absorbance of the simulated cell, then study the effect of impurity photovoltaic effect on the responsivity and internal quantum efficiency using the Shockley-Read-Hall model. It is found that the internal flux inside the simulated Lambertian cell could be enhanced as much as 25 times as a result of light trapping. Maximum responsivity and internal quantum efficiency of the simulated cell was obtained at a wavelength around 1 mum and 10(17) cm(-3) indium concentration. Near infrared response of the simulated cell is improved due to the enhancements of sub-band gap response by indium doping. To compare the mathematical model with the practical results, few samples of In-doped n-type silicon structures have been fabricated using the thermal vacuum resistive technique. Maximum responsivity and maximum internal quantum efficiency are obtained at wavelength 0.9-1 mum and 3.96x10(17) cm(-3) indium concentration. The results of the simulated and practical cells agree. (C) 2002 Elsevier Science Lid. All rights reserved.