Design of Si-rich nitride interposer waveguides for efficient light coupling from InP-based QD-emitters to Si₃N₄...

Area of Science:

• Photonics and Materials Science
• Integrated Optics
• Semiconductor Device Integration

Background:

• Monolithic integration of active and passive photonic components is crucial for advanced optical systems.
• Silicon nitride (Si3N4) platforms offer low loss and CMOS compatibility, but interfacing with active materials like Indium Phosphide (InP) presents challenges.
• Efficient coupling between different material systems is essential for realizing high-performance integrated photonic devices.

Purpose of the Study:

• To systematically analyze and design Si-rich-nitride (SRN) based interposer waveguide layers for interfacing InP-based active devices with Si3N4 passive waveguides.
• To investigate three different interposer designs, optimizing for coupling loss and back reflections while considering fabrication complexity.
• To evaluate the fabrication tolerance of the proposed coupling scheme and assess the performance of a novel, tunable SRN material.

Main Methods:

• Extensive 2D-eigenvalue and 3D-Finite-Difference Time-Domain (FDTD) electromagnetic simulations were employed.
• Real refractive index values for the SRN interposer were obtained from ellipsometry measurements of a newly developed ultra-Si-rich-nitride material.
• Test structures with 500x500nm2 waveguides fabricated via e-beam lithography were used to measure propagation losses.

Main Results:

• Three interposer designs were analyzed, offering trade-offs between coupling performance and fabrication complexity.
• The novel SRN material exhibits tunable refractive index with low-stress, crack-free samples up to 500nm thickness.
• Propagation losses of 15dB/cm were measured for the SRN waveguides, comparable to amorphous silicon-rich nitride (aSi:N) materials.
• The proposed coupling scheme demonstrates resilience to fabrication misalignments.

Conclusions:

• The developed SRN interposer designs enable efficient coupling between InP-based active devices and Si3N4 waveguides for monolithic integration.
• The novel SRN material and coupling concept are compatible with GaAs-based lasers and devices like SOAs and modulators.
• Designs are compatible with low-cost 248nm DUV lithography, enhancing the cost-effectiveness of Si3N4 platforms.
• This work paves the way for versatile, low-cost, high-performance monolithic InP-Quantum-Dot (QD)/Si3N4 platforms on silicon substrates.