Comparing Fourier transform infrared spectroscopy results with photocurrent measurements for Ge-on-Si PIN photodetectors with and without Al nanoantennas

Plasmonic and nanophotonic structures have been used to enhance the performance of photonic devices through the control and manipulation of photonic energy. Characterization of such devices typically requires the fabrication of contacting structures followed by stepwise spectral illumination and data recording. The acquisition of reflectance and transmittance spectra with Fourier transform infrared spectroscopy (FTIR) is—in contrast—a contactless and faster process. Since FTIR measurements take into account substrate absorption, which does not contribute to photocurrent, the two measurement approaches cannot be compared without further data processing. Here, we present a strategy to separate substrate absorption from absorption processes within the device layers in order to predict device performance from FTIR measurements. We apply our strategy to Ge-on-Si planar photodetectors with and without plasmonic structures.