Enhanced second-harmonic generation in strained germanium-on-insulator microdisks for integrated quantum photonic...

Area of Science:

• Quantum photonics
• Nonlinear optics
• Materials science

Background:

• Quantum photonic circuits promise superior performance over classical electronics.
• Second-order nonlinear (χ(2)) processes are crucial for quantum photonic components.
• CMOS-compatible materials like silicon (Si) and germanium (Ge) lack intrinsic χ(2) response due to centrosymmetry.

Purpose of the Study:

• To investigate the effect of strain on second-harmonic generation (SHG) in germanium.
• To enhance the nonlinear susceptibility (χ(2)) in CMOS-compatible materials for quantum photonics.
• To demonstrate a method for improving SHG signal in germanium.

Main Methods:

• Fabrication of germanium-on-insulator (GOI) microdisks.
• Deposition of a silicon nitride (Si3N4) stressor layer to induce strain in Ge.
• Experimental observation of SHG under femtosecond optical pumping with varying strain levels.

Main Results:

• Strain was successfully applied to Ge microdisks, deforming their centrosymmetric unit cell structure.
• A clear trend of increasing SHG signal with increasing strain was observed.
• SHG conversion efficiencies were boosted by up to 300% compared to unstrained control samples.

Conclusions:

• Strain engineering effectively enhances the nonlinear χ(2) susceptibility in germanium.
• This technique enables CMOS-compatible materials to exhibit significant nonlinear optical properties.
• The findings open new avenues for integrating nonlinear functionalities into semiconductor-based photonic circuits.