The performance limit of monocrystalline silicon solar cells is almost reached. Only marginal effects are limiting the excess carrier lifetime of nowadays used materials. Nonetheless it is interesting to investigate and characterize the limiting effects to improve the performance even further and to deepen the understanding, enabling new approaches and novel cell structures. This thesis tries to characterize limiting defect in high standard Gallium doped silicon via lifetime spectroscopy. To assess the validity of the results, the limits of this commonly used method (lifetime spectroscopy) are analyzed by evaluation of simulated lifetime data. Further, a guideline for future lifetime evaluations is given which can improve the outcome of the complex evaluation and helps differentiate between bulk and surface effects.