Broadband PureGaB Ge-on-Si photodiodes responsive in the ultraviolet to near-infrared range

Tihomir Knezević, Max Krakers, Lis K. Nanver

Research output: Chapter in Book/Report/Conference proceedingConference contributionAcademicpeer-review

2 Citations (Scopus)
46 Downloads (Pure)


Optical characterization of PureGaB germanium-on-silicon (Ge-on-Si) photodiodes was performed for wavelengths between 255 nm and 1550 nm. In PureGaB technology, chemical vapor deposition is used to grow germanium islands in oxide windows to the silicon substrate and then cap them in-situ with nm-thin layers of first gallium and then boron, thus forming nm-shallow p+n diodes. These PureGaB Ge-on-Si photodiodes are CMOS compatible and characterized by low leakage currents. Here they are shown to have high responsivity in the whole ultraviolet (UV) to near infrared (NIR) wavelength range. Particularly, two sets of diodes were studied with respect to possible detrimental effects of the Al metallization/alloying process steps on the responsivity. Al-mediated transport of the Ge and underlying Si was observed if the PureGaB layer, which forms a barrier to metal layers, did not cover all surfaces of the Ge islands. A simulation study was performed confirming that the presence of acceptor traps at the Ge/Si interface could decrease the otherwise high theoretically attainable responsivity of PureGaB Ge-on-Si photodiodes in the whole UV to NIR range. A modification of the device structure is proposed where the PureGaB layer covers not only the top surface of the Ge-islands, but also the sidewalls. It was found that to mitigate premature breakdown, it would be necessary to add p-doped guard rings in Si around the perimeter of Ge islands, but this PureGaB-all-around structure would not compromise the optical performance.

Original languageEnglish
Title of host publicationOptical Components and Materials XVII
EditorsShibin Jiang, Michel J. F. Digonnet
ISBN (Electronic)9781510633155
Publication statusPublished - 3 Mar 2020
EventOptical Components and Materials XVII 2020 - San Francisco, United States
Duration: 4 Feb 20206 Feb 2020
Conference number: 27

Publication series

NameProceedings of SPIE - The International Society for Optical Engineering
ISSN (Print)0277-786X
ISSN (Electronic)1996-756X


ConferenceOptical Components and Materials XVII 2020
Country/TerritoryUnited States
CitySan Francisco


  • Broadband photodiode
  • Ge diodes
  • Ge-on-Si
  • Light emission measurements
  • Near-infrared photodiode
  • Pure gallium and pure boron (PureGaB)
  • Responsivity
  • Simulations
  • Ultraviolet photodiode
  • 22/3 OA procedure


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