Dec 24, 2018

Formation of Tensilely Strained Germanium-on-Insulator

We fabricate a high-quality germanium-on-insulator (GOI) with tensile strain by combining the wafer bonding of a strained Ge grown on a Si substrate and an oxidized Si substrate and the selective etching of Si. The obtained 300-nm-thick strained GOI shows a smooth surface with RMS roughness of 0.15 nm and no dislocation is detected by cross-sectional transmission electron microscopy (XTEM). The tensile strain of 0.19% induced in the GOI is found to be maintained throughout the fabrication process. This suggests that the fabricated strained GOI has a high potential as an essential platform for high-performance electronic and optical devices.


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Dec 10, 2018

Spin-on doping of germanium-on-insulator wafers for monolithic light sources on silicon

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 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.


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