Measured absorption spectra for bulk silicon and GeNW arrays and simulated spectral absorbance. (a) Absorption spectra for bulk silicon and a GeNW array with NWs of 2 µm in length, 80 nm in diameter and 150 nm pitch situated on a glass substrate. The measured GeNW spectrum was extracted from Fan et al. . The spectra were measured and simulated with a homogenous, non-wavelength-dependent illumination and are therefore not weighted with an AM1.5G spectrum. (b) Simulated spectral absorbance for a substrate-free SiNW array equal in its arrangement to the aforementioned GeNW array and in comparison to a Si membrane of 2 µm in thickness.