A Foundry-Compatible Plasmonic Material Platform Based on Heavily Doped Epitaxial Germanium-on-Silicon

Michele Ortolani Physics Department, Sapienza University of Rome, Rome, Italy Jacopo Frigerio LNESS, Laboratory for Nanostructure Epitaxy and Spintronics on Silicon, Como, Italy Physics Department, Politecnico di Milano, Milan, Italy Leonetta Baldassarre Center for Life and Nano Sciences, Istituto Italiano di Tecnologia, Rome, Italy Valeria Giliberti Physics Department, Sapienza University of Rome, Rome, Italy Emilie Sakat Physics Department, Politecnico di Milano, Milan, Italy Paolo Biagioni Physics Department, Politecnico di Milano, Milan, Italy Giovanni Isella LNESS, Laboratory for Nanostructure Epitaxy and Spintronics on Silicon, Como, Italy Physics Department, Politecnico di Milano, Milan, Italy

Replacing metals with thin-film semiconductor materials with high carrier density could led to a new generation of plasmonic devices, where plasmonic elements are integrated with standard electronic platforms [1]. In this framework, the most attractive thin-film materials are those whose growth is compatible with silicon foundry processes and silicon substrates. One notable example is electron-doped germanium (n-Ge), which features a small effective mass of 0.12 and supports heavy doping levels up to 3×10¹⁹ cm^-3 hence allowing plasma frequencies up to the mid-infrared range.

In this work, we measured the optical and electrical transport properties of n-Ge thin films hetero-epitaxially grown on silicon substrates by plasma-enhanced chemical vapor deposition (PE-CVD). From normal-incidence reflectivity measurements and Hall-transport data taken on the as-grown materials as a function of temperature and dopant incorporation levels, we derived a phenomenological model of electron scattering from optical and acoustic phonons, charged impurities (donors and charged dislocations) and neutral impurities (crystal defects and neutral disclocations). The Kramers-Kronig relations were finally employed to calculate the complex dielectric function directly from the optical data in a model-free fashion, in order to perform electromagnetic simulations of plasmonic devices.

The research leading to these results has received funding from the European Union’s Seventh Framework Programme under grant agreement n°613055.

[1] G. V. Naik, V. M. Shalaev and A. Boltasseva, Advanced Materials 25, 3264 (2013)

Dielectric function and Hall mobility of the germanium thin films grown on silicon wafers for integrated plasmonic devices

giliberti.valeria@gmail.com