Emerging technology for future VCSELs
Résumé
The global VCSEL (vertical-cavity surface-emitting laser) market is developing dynamically, with laser production projected to triple in the next five years. One of the driving forces behind this growth is VCSEL's wide application in the photonics industry, including short-distance communication systems, LIDARs, time-of-flight sensors, autonomous vehicles, robots, and drones. In this work, we present the epitaxial growth by MOVPE of VCSEL epi-structures grown on GaAs for various applications and a novel VCSEL epi-structure using germanium (Ge) substrates instead of traditional gallium arsenide. The critical challenge in this development is to achieve high crystal quality of grown GaAs/AlGaAs layers on Ge substrates while taking advantage of a better crystallographic lattice sameness between Ge and AlGaAs, which reduces misfit defects density and increases the quantum efficiency of the device. Germanium, offering higher yield and fewer production losses due to higher uniformity at larger-size wafers, is promised to lower the environmental impact compared to more expensive GaAs substrate. With the demand for VCSELs growing and technical requirements becoming more rigorous, there is a need to scale to larger wafer diameters and demonstrate a path for integration with CMOS technology. These epitaxial technological efforts, with particular attention paid to the growth mechanism of nucleation layer bridging Ge substrate with GaAs/AlGaAs epi-stack, were supported by several characterization methods to be used as X-ray diffraction and topography, depth high-resolution SIMS, electron microscopy (SEM/TEM), atomic force microscopy, Nomarsky optical microscopy, PL mapping, ECV, Hall, optical spectroscopy, reflectance, epi-wafer bowing measurements. The aim was to discover differences and critical parameters of VCSEL structure grown on Ge substrates versus GaAs at the material characterization level and to develop and produce VCSELs ready for use in the demonstrators. The VCSEL/Ge device epi- technology developed at VIGO Photonics is industrial-oriented for mass production on up to 6- or 8-inch Ge wafers, offering different architecture configurations in relation to the specifications of the targeted applications. The goal is to meet the demand of the constantly growing photonics market by providing a novel solution that will increase production yield, reduce defectivity, and introduce reduced environmental impact. Moreover, the project findings can be developed into usable tools bringing innovative change across various end-user industries (e.g., automotive, smartphone, 3D sensing technologies, and others). The PhotoGeNIC project has received funding from the European Union’s Horizon Europe research and innovation programme under grant agreement No. 101069490