Application of photoconductivity decay and photocurrent generation methods for determination of minority carrier lifetime in silicon

摘要

Minority carrier lifeline, tau, is one of the most important parameters which has a decisive effect on the performance of silicon devices based on excess carriers. The value of tau is greatly affected by the presence of impurities and defects in silicon and its value provides a fair indication of quality of the material. Photoconductivity decay (PCD) and photocurrent generation (PCG) methods are simple and low cost methods of measurement of minority carrier lifetime in silicon wafers. However, their application requires care. The PCD method can give quite misleading results in case of polycrystalline wafers if there exists potential barriers at the grain boundaries which may affect majority carrier mobility significantly. PCG needs creation of an induced p~+-p-n~+ structure of substantially good quality that should not degrade with time. For PCG method the tau measurement under vacuum conditions provides correct and consistent results.