Photocurrent modeling at high dose rates

An analytical steady-state photocurrent model that includes ohmic field effects and treats (nonlinear) ambipolar diffusion and nonlinear recombination effects explicitly is developed. The nonlinear recombination and ambipolar diffusion are solved exactly, and the asymptotic ohmic field is treated as an approximate perturbation with fitted parameters. The model is found to be in good agreement with numerical calculations and with experimental results. Appropriate Taylor series expansions and extensive parametric studies using the model indicate that the superlinear response is largest and occurs at smaller dose rates in relatively high-resistivity materials that have a long excess carrier lifetime and, if the material is n-type, a large τ _no/τ_po ratio. The nonlinearity is more pronounced for infinite-medium devices. For this reason, power devices are expected to exhibit more nonlinear behavior than integrated circuit devices