PhotoGeNIC

Vertical-cavity surface-emitting lasers (VCSELs) are a type of semiconductor laser diodes with laser beam emission perpendicular from the top surface. They are a key component in various laser products. Most VCSELs are grown on gallium arsenide substrates, but recently germanium (Ge) has attracted significant research attention as a substrate candidate. The EU-funded PhotoGeNIC project aims to grow VCSELs on germanium using molecular beam epitaxy and metal-organic chemical vapour deposition. The key challenge is to achieve high crystal quality of the grown layers, decrease misfit dislocations (defects that severely degrade material properties) and increase the quantum efficiency of the laser device.

The project scope is to develop an innovative technology of germanium (Ge)-based VCSEL. The main objective is to develop a Ge-VCSEL epi-growth by MOCVD and MBE techniques and processing of high performance and reliable lasers to be integrated in 3D camera and LiDAR demonstrators. The key challenge is to achieve high crystal quality of grown layers while taking the advantage of a better crystallographic lattice sameness between Ge and Al gallium arsenide (GaAs), which enables to decrease misfit defects density and in consequence to increase the quantum efficiency of the device. Several characterisation methods will be used as X-ray diffraction and topography, depth high resolution SIMS, electron microscopy (SEM/TEM), atomic force microscopy, reflectance, PL mapping, and others. Each growing campaign will be concluded by processing of conventional VCSELs (GaAs-based) and VCSELs on Ge which will allow the verification of VCSELs parameters and comparison of both type devices. The VCSEL technology drives a dynamic market with constant need for innovative solutions. Demonstration of high performing devices of Ge-on-Si can unlock potentially large markets from optical data communications to imaging, lighting and displays, to the manufacturing sector, to life sciences, health care, security and safety. In commercial applications, the performance, costs and the strong reduction of toxic elements will be very important factors to drive a replacement of the current technology. The Ge, offering a higher yield and less production losses due to higher uniformity at larger size wafer, is promised to lower the environmental burden compared to expensive GaAs substrate. As the VCSEL sector is developing dynamically with laser production expected to triple in the next five years, the project, with its innovative Ge-VCSEL solution, has the potential to significantly contribute to the reduction of lasers' global usage of toxic materials, and improve the device performances.