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<p>The development of germanium-based mid-infrared (MIR) optoelectronic technologies is central to advancing compact, high-performance on-chip systems. While plasmonic field enhancement in heavily-doped semiconductors is widely exploited to intensify light-matter interactions, yet <i>p-</i>type germanium has been discarded due to its complex valence band structure. Here, we show that heavily-doped <i>p-</i>type germanium exhibits a dual light-matter interaction, where an ε-near-zero band delineates a plasmonic-like regime below the plasma frequency and a broadband absorption (dominated by inter-subband transitions) above it. This duality extends the spectral range of strong interaction beyond conventional Drude plasmonics. Using the Czochralski method, we have grown high-quality heavily-doped germanium single crystals with gallium concentrations up to ~2×10<sup>20 </sup>cm<sup>−3</sup>, exhibiting a high, near 100% acceptor activation. Mid-infrared spectroscopic ellipsometry and reflectance measurements reveal a continuous blue shift of the plasma wavelength with increasing dopant concentration, up to 4.5 μm, the shortest wavelength reported in Ge to date. Our findings manifest the potential of heavily-doped <i>p-</i>type bulk germanium crystals for applications that benefit from strong mid-infrared absorption and high crystal lattice quality.</p>

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Enhanced mid-infrared light-matter coupling in heavily-doped p-germanium due to interplay between plasmonic and inter-subband contributions

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年6月25日

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  • Aravind N. Subramanian,
  • Saud Bin Anooz,
  • Sergey G. Pavlov,
  • Carsten Richter,
  • Géza Szántó,
  • Mariia Sidorova,
  • Peter Petrik,
  • R. Radhakrishnan Sumathi

摘要

The development of germanium-based mid-infrared (MIR) optoelectronic technologies is central to advancing compact, high-performance on-chip systems. While plasmonic field enhancement in heavily-doped semiconductors is widely exploited to intensify light-matter interactions, yet p-type germanium has been discarded due to its complex valence band structure. Here, we show that heavily-doped p-type germanium exhibits a dual light-matter interaction, where an ε-near-zero band delineates a plasmonic-like regime below the plasma frequency and a broadband absorption (dominated by inter-subband transitions) above it. This duality extends the spectral range of strong interaction beyond conventional Drude plasmonics. Using the Czochralski method, we have grown high-quality heavily-doped germanium single crystals with gallium concentrations up to ~2×1020 cm−3, exhibiting a high, near 100% acceptor activation. Mid-infrared spectroscopic ellipsometry and reflectance measurements reveal a continuous blue shift of the plasma wavelength with increasing dopant concentration, up to 4.5 μm, the shortest wavelength reported in Ge to date. Our findings manifest the potential of heavily-doped p-type bulk germanium crystals for applications that benefit from strong mid-infrared absorption and high crystal lattice quality.