Investigation of Ge component cells

In this paper we investigate germanium (Ge) component cells with respect to their suitability as test structures for irradiation experiments and as reference cells. It will be demonstrated by means of spectral response measurements that Ge component cells do not exhibit the same behavior as a Ge subcell in the complete triple-junction (3J) device. Photon recycling from upper layers (GaInP, GaInAs) results in large signals in shorter wavelength regions. This leads to a higher photocurrent in the Ge component cell compared to the Ge subcell. In this paper it will be shown that this effect places restrictions on the suitability of Ge component cells for the above mentioned purposes. Possible solutions for each of the mentioned applications of Ge component cells are presented.