A relatively simple, yet complete analytical model for predicting the performance of illuminated or unilluminated (dark) pn diodes with arbitrary doping profiles is developed and presented in this dissertation. It can be used to calculate the saturation current, minority carrier density, short circuit current, spectral response, and effective low-high (p-p⁺) junction recombination velocities of such diodes. The model is applied to dark or illuminated n⁺-p-p⁺ diodes as a function of the front and back surface recombination velocities and the bulk doping profiles. The analysis includes heavy doping effects. The results predicted by this model are compared with those predicted by numerical simulation programs. Both results agree well with each other and with the experimental data available. The complete analytical expressions produced by the model can be reduced to simpler forms for the transparent and quasi-transparent cases. These forms agree with the special case expressions developed by others. The new model is a substantial contribution leading to improved understanding of such devices.