Monolithically integrated 940 nm VCSELs on bulk Ge substrates

• DOI: 10.1364/oe.513997
• Publication Date: 2024-01-31T10:00:06Z
• Authors: Zeyu Wan; Yun-Cheng Yang; Wei-Hsin Chen; Chih-Chuan Chiu; Yunlong Zhao; Markus Feifel; Lukas Chrostowski; David Lackner; Chao-Hsin Wu; Guangrui Xia

This research successfully developed an independent Ge-based VCSEL epitaxy and fabrication technology route, which set the stage for integrating AlGaAs-based semiconductor devices on bulk Ge substrates. This is the second successful Ge-based VCSEL technology reported worldwide and the first Ge-based VCSEL technology with key details disclosed, including Ge substrate specification, transition layer structure and composition, and fabrication process. Compared with the GaAs counterparts, after epitaxy optimization, the Ge-based VCSEL wafer has a 40% lower surface root-mean-square roughness and 72% lower average bow-warp. After device fabrication, the Ge-based VCSEL has a 10% lower threshold current density and 19% higher maximum optical differential efficiency than the GaAs-based VCSEL.