title: Spectral reflectance and responsivity of Ge- and InGaAs-photodiodes in the near-infrared: measurement and model.
abstract: The spectral reflectance and responsivity of Ge- and InGaAs-photodiodes at (nearly) normal and oblique incidence (45 degrees) were investigated. The derived data allow a calculation of the photodiodes responsivities for any incident angle. The measurements were carried out with s- and p-polarized radiation in the wavelength range from 1260 to 1640 nm. The spectral reflectance of the photodiodes was modeled by using the matrix approach developed for thin-film optical assemblies. The comparison between the calculated and measured reflectance shows a difference of less than 2% for the Ge-photodiode. For the InGaAs-photodiode, the differences between measured and calculated reflectance are larger, i.e., up to 6% for wavelengths between 1380 and 1580 nm. Despite the larger differences between calculated and measured spectral reflectances for the InGaAs-photodiode, the difference between calculated and measured spectral responsivity is even smaller for the InGaAs-photodiode than for the Ge-photodiode, i.e., < or =1.2% for the InGaAs-photodiode compared to < or =2.2% for the Ge-photodiode. This is because the difference in responsivity is strongly correlated to the absolute spectral reflectance level, which is much lower for the InGaAs-photodiode. This observation also shows the importance of having small reflectances, i.e., appropriate antireflection coatings for the photodiodes. The relative standard uncertainty associated with the modeled spectral responsivity is about 2.2% for the Ge-photodiode and about 1.2% for the InGaAs-photodiode for any incident angle over the whole spectral range measured. The data obtained for the photodiodes allow the calculation of the spectral responsivity of Ge- and InGaAs-trap detectors and the comparison with experimental results.
authors.affiliation: Optics Division, Physikalisch-Technische Bundesanstalt, 38116 Braunschweig, Germany. marco.lopez@ptb.de
authors.forename: M
authors.initials: M
authors.lastname: López
authors.forename: H
authors.initials: H
authors.lastname: Hofer
authors.forename: K D
authors.initials: KD
authors.lastname: Stock
authors.forename: J C
authors.initials: JC
authors.lastname: Bermúdez
authors.forename: A
authors.initials: A
authors.lastname: Schirmacher
authors.forename: F
authors.initials: F
authors.lastname: Schneck
authors.forename: S
authors.initials: S
authors.lastname: Kück