Simulations of photoconductivity and lifetime for steady state and nonsteady state measurements

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Abstract
Contact less measurements of the minority carrier “lifetime” and the photoconductivity are widely used to characterize the material quality and to investigate defects in a sample. In order to interpret these measurements correctly and to guarantee comparability between different methods, numerical simulation tools were developed. These simulations allow to account even for very complex defect models, thus, e.g., enabling the simulation of trapping effects. Contrary to the Shockley–Read–Hall model or the widely used simulation tool PC1D nearly no assumptions are made. Furthermore, nonsteady state solutions can be obtained. The simulation approach is explained in detail, along with simulations of the trapping effect on the measured lifetime for different injections, trap parameters, and measuring methods, demonstrating the capabilities of the here presented simulation tool. Temperature and injection dependent lifetime measurements were performed and it is shown how important sample parameters can be extracted using the simulation tool. Additionally an approach is presented to simulate lifetimes for thick samples, where a nonuniform carrier profile has to be taken into account. This enables a comparison of nonsteady state to steady-state lifetime measurement techniques even for thick samples such as ingots.

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