Second Harmonic Generation in Germanium Quantum Wells for Nonlinear Silicon Photonics
Journal article, 2021
Second-harmonic generation (SHG) is a direct measure of the strength of second-order nonlinear optical effects, which also include frequency mixing and parametric oscillations. Natural and artificial materials with broken center-of-inversion symmetry in their unit cell display high SHG efficiency, however, the silicon-foundry compatible group IV semiconductors (Si, Ge) are centrosymmetric, thereby preventing full integration of second-order nonlinearity in silicon photonics platforms. Here we demonstrate strong SHG in Ge-rich quantum wells grown on Si wafers. Unlike Si-rich epilayers, Ge-rich epilayers allow for waveguiding on a Si substrate. The symmetry breaking is artificially realized with a pair of asymmetric coupled quantum wells (ACQW), in which three of the quantum-confined states are equidistant in energy, resulting in a double resonance for SHG. Laser spectroscopy experiments demonstrate a giant second-order nonlinearity at mid-infrared pump wavelengths between 9 and 12 μm. Leveraging on the strong intersubband dipoles, the nonlinear susceptibility χ(2) almost reaches 105 pm/V, 4 orders of magnitude larger than bulk nonlinear materials for which, by the Miller's rule, the range of 10 pm/V is the norm.
germanium
nonlinear optics
silicon photonics
mid-infrared
quantum wells
Author
Jacopo Frigerio
Polytechnic University of Milan
Chiara Ciano
Universita degli studi - Roma Tre
Joel Kuttruff
University of Konstanz
Andrea Mancini
Sapienza University of Rome
Ludwig Maximilian University of Munich (LMU)
Andrea Ballabio
Polytechnic University of Milan
Daniel Chrastina
Polytechnic University of Milan
Virginia Falcone
Polytechnic University of Milan
Monica De Seta
Universita degli studi - Roma Tre
L. Baldassarre
Sapienza University of Rome
Jonas Allerbeck
University of Luxembourg
University of Konstanz
Daniele Brida
University of Luxembourg
Lunjie Zeng
Chalmers, Physics, Nano and Biophysics
Eva Olsson
Chalmers, Physics, Nano and Biophysics
Michele Virgilio
University of Pisa
M. Ortolani
Sapienza University of Rome
ACS Photonics
2330-4022 (eISSN)
Vol. 8 12 3573-3582Areas of Advance
Nanoscience and Nanotechnology
Subject Categories
Atom and Molecular Physics and Optics
Other Physics Topics
Condensed Matter Physics
Infrastructure
Chalmers Materials Analysis Laboratory
DOI
10.1021/acsphotonics.1c01162