A comprehensive model of four layered MINP+ (metal-tunnel insulator - NP+ semiconductor) structure incorporating an inhomogeneous impurity doping profile is numerically simulated. The influence of built-in electric field in the device on its performance is investigated. The drift fields are the result of the nonuniformaly doped semiconductor. The dependence of the minority carrier lifetime and mobility on the doping density are taken into account. Solution curves for the complete set of transport, continuity and Poisson equations for the device as solar cell are obtained. Significant device parameters are identified and model calculations are carried out over a range covering most physically realizable values for these parameters. The I-V characteristics are calculated as a function of insulator thickness, metal workfunction, substrate doping density and semiconductor thickness with present semiconductor fabrication technology.