No bow in epi-wafer
A comparison test * showed that the bow on a gallium arsenide (GaAs) wafer is 10 times as high than on the germanium (Ge) wafer, 230 µm on the GaAs and 25 µm on Ge. This results in a better yield of subsequent production processes, which has a positive effect on costs.
Better lattice match than GaAs
GaAs / AlxGa(1-x) As / AlAs are the preferred materials for VCSEL DBR mirrors.
The graph shows that the DBR will have a slight lattice mismatch with the GaAs wafer, which causes bow in the final epi-wafer.
Longer wavelength VCSEL’s are therefore difficult to make due to the need for ever thicker DBR structures to match the λ/4.
The graph shows that germanium is better lattice-matched to the DBR than GaAs and bow is  negligible.
Ready for longer wavelengths > 1,3µm
The lower bow makes design of safe-eye longer wavelengths >1.3 µm VCSELs possible, such as long-range LiDAR (>200 m).