Procedures for measuring the spectral response of multi-junction cells in general require variation of the bias spectrum and voltage biasing. It is shown that a refined procedure including optimization of bias spectrum and voltage is necessary to minimize a measurement artifact, which appears if the subcell under test has non-ideal properties, such as a low shunt resistance or a low reverse breakdown voltage. This measurement artifact is often observed on measuring the spectral response of the Ge bottom cell of GaInP/Ga(In)As/Ge triple-junction cells. The main aspect of the measurement artifact is that the response of another subcell is simultaneously measured, while at the same time the signal of the Ge subcell is too low. Additionally, the shape of the spectral response curve is influenced under certain measurement conditions. In this paper the measurement artifact is thoroughly discussed by measurement results and simulation. Based on this analysis, a detailed procedure for the spectral response measurement of multi-junction cells is developed, specially designed to minimize such measurement artifacts

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A method to visualize and investigate radiative recombination processes in compound semiconductor materials by utilizing the effect of optical coupling in III-V multilayer systems is presented. For this purpose, a semiconductor material of interest is grown on an activated germanium (Ge) substrate which then serves as a photodiode. By means of spectral response measurements of the Ge photodiode, a response signal from the upper layers can be detected. It is proven both by experiment and by modeling that the signals from these layers can only be explained by optical transport mechanisms, i.e., radiative recombination

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