Design and fabrication of strained light emitting germanium microstructures by liquid phase epitaxy

Ünlü, Buse
Germanium is compatible with CMOS technology and can be utilized for the development of an integrated laser on Si platforms. Nevertheless, it is a very inefficient light emitter owning to its indirect bandgap. On the other hand, the application of tensile strain reduces the split in between direct and indirect band edges of Ge, which in turn enhances its light emission efficiency, and converts it into a direct bandgap material. In this thesis, firstly finite element model simulations are performed to determine the dimensions of the most efficient Ge microstructures providing the highest possible biaxial and uniaxial strain levels. Following that, Ge microstructures are fabricated, in which silicon nitride acts as a stressor layer on top and sides. Radio frequency magnetron sputtering, a straightforward, low-cost, and environmentally friendly method, is used for both amorphous Ge and the stressor film deposition processes. The liquid phase epitaxy technique is utilized to crystallize the amorphous Ge. It is demonstrated that one single annealing step converts the Ge to a single crystal and induces tensile stress to the nitride film, simultaneously. Moreover, the proceeding wet chemical etching steps promote the tensile strain induction in the Ge microstructures. The amount of strain can easily be tuned by changing the type and duration of wet etching processes. A uniaxial strain level of up to 3.5% has been demonstrated by Raman and micro photoluminescence spectroscopy, and verified by FEM simulations. Results of this study pave the way to obtain infrared Ge lasers on Si chips by utilizing cost-efficient and easy-to-use deposition and crystallization techniques.


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Citation Formats
B. Ünlü, “Design and fabrication of strained light emitting germanium microstructures by liquid phase epitaxy,” M.S. - Master of Science, Middle East Technical University, 2021.