  High quality 940 nm Al$_x$Ga$_{1-x}$As n-type distributed Bragg reflectors
(DBRs) were successfully monolithically grown on off-cut Ge (100) substrates.
The Ge-DBRs have reflectivity spectra comparable to those grown on conventional
bulk GaAs substrates and have smooth morphology, reasonable periodicity and
uniformity. These results strongly support VCSEL growth and fabrication on more
scalable bulk Ge substrates for large scale production of AlGaAs-based VCSELs.
