High electron doping of germanium (Ge)
is considered to be an important process to convert Ge into an optical gain
material and realize a monolithic light source integrated on a silicon chip.
Spin-on doping is a method that offers the potential to achieve high doping
concentrations without affecting crystalline qualities over other methods such
as ion implantation and in-situ doping during material growth. However, a
standard spin-on doping recipe satisfying these requirements is not yet
available. In this paper we examine spin-on doping of Ge-on-insulator (GOI)
wafers. Several issues were identified during the spin-on doping process and
specifically the adhesion between Ge and the oxide, surface oxidation during
activation, and the stress created in the layers due to annealing. In order to
mitigate these problems, Ge disks were first patterned by dry etching followed
by spin-on doping. Even by using this method to reduce the stress, local
peeling of Ge could still be identified by optical microscope imaging.
Nevertheless, most of the Ge disks remained after the removal of the glass.
According to the Raman data, we could not identify broadening of the lineshape
which shows a good crystalline quality, while the stress is slightly relaxed.
We also determined the linear increase of the photoluminescence intensity by
increasing the optical pumping power for the doped sample, which implies a
direct population and recombination at the gamma valley.
Source:IOPscience
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