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<p>High-speed germanium photodetectors are essential for silicon photonics, but thin germanium absorbers typically exhibit limited absorption at 1550 nm. This work studies a resonant-cavity-enhanced germanium-on-silicon photodetector that combines dielectric cavity confinement, plasmonic near-field localization, and a transparent electrode to improve telecom-band detection. Alternating silicon dioxide and titanium dioxide multilayers form a bottom distributed Bragg reflector and a top dielectric coating, creating an optical cavity that boosts field intensity in the absorber. In the simple configuration, the top dielectric coating functions as an anti-reflection coating (ARC), whereas in the symmetric configuration it acts as a top dielectric partial reflector (TDPR). Plasmonic enhancement is achieved by embedding gold nanoparticles inside the germanium layer, with nanoparticle diameter and embedding depth optimized for strong optical localization. A graphene layer is integrated as a low-loss transparent electrode to support carrier extraction while preserving cavity response. Three-dimensional finite-difference time-domain simulations show that optimized structures achieve total optical absorption values of 0.7676 and 0.6593 at 1550 nm for the simple and symmetric cavity designs, respectively. The corresponding absorption-limited responsivities are approximately 0.718 A/W and 0.618 A/W for the simple and symmetric structures, respectively, assuming ideal carrier collection and no internal gain. Photovoltaic operation is evaluated under 1550 nm illumination at 0.5 mW incident optical power. The simple cavity provides higher useful optical-to-electrical response, while the symmetric cavity offers stronger resonant field confinement and a more pronounced standing-wave distribution. These results demonstrate the potential of combining dielectric cavity engineering, plasmonic near-field localization, and graphene-assisted carrier extraction for compact Ge-on-Si near-infrared photodetectors. The proposed architecture is presented as a theoretical optical-electrical proof-of-concept, with practical performance depending on material quality, interface recombination, and contact-related losses.</p>

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Hybrid cavity–plasmonic germanium photodetector architecture for high-responsivity near-infrared detection

  • 期刊论文

  • 发表日期：

    2026年7月14日

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  • Mohammad Abbaszadeh,
  • Saeed Golmohammadi,
  • Hamed Baghban

摘要

High-speed germanium photodetectors are essential for silicon photonics, but thin germanium absorbers typically exhibit limited absorption at 1550 nm. This work studies a resonant-cavity-enhanced germanium-on-silicon photodetector that combines dielectric cavity confinement, plasmonic near-field localization, and a transparent electrode to improve telecom-band detection. Alternating silicon dioxide and titanium dioxide multilayers form a bottom distributed Bragg reflector and a top dielectric coating, creating an optical cavity that boosts field intensity in the absorber. In the simple configuration, the top dielectric coating functions as an anti-reflection coating (ARC), whereas in the symmetric configuration it acts as a top dielectric partial reflector (TDPR). Plasmonic enhancement is achieved by embedding gold nanoparticles inside the germanium layer, with nanoparticle diameter and embedding depth optimized for strong optical localization. A graphene layer is integrated as a low-loss transparent electrode to support carrier extraction while preserving cavity response. Three-dimensional finite-difference time-domain simulations show that optimized structures achieve total optical absorption values of 0.7676 and 0.6593 at 1550 nm for the simple and symmetric cavity designs, respectively. The corresponding absorption-limited responsivities are approximately 0.718 A/W and 0.618 A/W for the simple and symmetric structures, respectively, assuming ideal carrier collection and no internal gain. Photovoltaic operation is evaluated under 1550 nm illumination at 0.5 mW incident optical power. The simple cavity provides higher useful optical-to-electrical response, while the symmetric cavity offers stronger resonant field confinement and a more pronounced standing-wave distribution. These results demonstrate the potential of combining dielectric cavity engineering, plasmonic near-field localization, and graphene-assisted carrier extraction for compact Ge-on-Si near-infrared photodetectors. The proposed architecture is presented as a theoretical optical-electrical proof-of-concept, with practical performance depending on material quality, interface recombination, and contact-related losses.