  Similar to other high quality crystalline absorbers, an accurate knowledge of
surface passivation of crystalline Germanium (c-Ge) substrates is crucial for a
straightforward improvement of photovoltaic device performance. For crystalline
silicon devices, this information is typically obtained by quasisteady state
photoconductance (QSS-PC) technique using Sinton WCT-120 tool. In this work, we
explore the conditions to adapt this measurement technique to c-Ge substrates.
Based on PC-1D simulations, we deduce that a minimum effective lifetime is
needed corresponding to an effective diffusion length equal to the substrate
thickness. Apart from this, an accurate estimation of the total photogeneration
inside the c-Ge sample is also mandatory. This condition implies that the light
intensity that impinges onto the sample must be measured with a c-Ge sensor,
although the integrated c-Si sensor can be used for high flash intensities.
Additionally, the optical factor used to evaluate sample reflectance must be
also known, which is determined by measuring robust effective lifetime values
under photoconductance decay conditions. Finally, knowledge about carrier
mobility in c-Ge is also necessary to translate the measured photoconductance
to the corresponding excess carrier density values. Lifetime measurements of
passivated c-Ge substrates done by QSS-PC technique are validated by comparing
them with the ones obtained by microwave photoconductance technique.
