Monolithically integrated 940 nm VCSELs on bulk Ge substrates.

Area of Science:

• Semiconductor Physics
• Materials Science
• Optoelectronics

Background:

• Developing Germanium (Ge)-based Vertical-Cavity Surface-Emitting Lasers (VCSELs) is crucial for integrating optoelectronic devices on silicon photonics platforms.
• Existing Ge-VCSEL technologies lack detailed process disclosures, hindering further development and adoption.

Purpose of the Study:

• To establish an independent epitaxy and fabrication process for Ge-based VCSELs.
• To enable the integration of Aluminum Gallium Arsenide (AlGaAs)-based semiconductor devices on bulk Ge substrates.
• To present a detailed account of the Ge substrate specifications, transition layer, and fabrication process for Ge-VCSELs.

Main Methods:

• Development of a unique Ge-based epitaxy process.
• Optimization of transition layer structure and composition for AlGaAs-on-Ge integration.
• Fabrication of Ge-based VCSEL devices.

Main Results:

• Achieved a 40% reduction in surface root-mean-square roughness and a 72% decrease in average bow-warp for Ge-based VCSEL wafers compared to GaAs counterparts.
• Demonstrated a 10% lower threshold current density for Ge-based VCSELs.
• Observed a 19% higher maximum optical differential efficiency in Ge-based VCSELs compared to GaAs-based VCSELs.

Conclusions:

• Successfully developed and disclosed a novel Ge-based VCSEL epitaxy and fabrication route.
• The developed Ge-based VCSEL technology offers superior wafer quality and enhanced device performance metrics over traditional GaAs VCSELs.
• This breakthrough paves the way for advanced heterogeneous integration of optoelectronic devices on Ge substrates.