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Defence in the field of Micro- and Nanotechnology M. Sc. (Tech.) Zhengjun Liu

The title of thesis is “Material and process engineering for cost-effective silicon technologies”

Conventionally, in semiconductor industry the device performance has been the main driving force while in photovoltaics the cost has been of utmost importance.  This work seeks for the balance between the cost-driven and performance-driven approaches. The traditional device performance perspective is covered by developing high-resolution focused ion beam (FIB) patterning processes while the cost perspective is covered by studying the applicability of inexpensive quasi-mono silicon (QM-Si) material. New insights from the opposite perspective are provided by developing boron implantation gettering strategies for high-performance n-type silicon solar cells and by studying the applicability of QM-Si beyond photovoltaics.
In this work, the phosphorus diffusion gettering method is implemented which effectively recovers the scrap QM-Si material by increase the minority carrier lifetime. This thesis also reports successful demonstration of boron implantation gettering by which the bulk iron point defect concentration is dramatically reduced, which facilitates further efficiency improvement of advanced n-type solar cells.

A novel FIB lithography method is developed for precisely defined nanoscale pattering with sub 100 nm resolution. FIB lithography is applied to patterning of QM-Si. The achieved submicron resolution in a line array suggests that the material has true potential e.g. in microelectromechanical systems (MEMS).

Opponent: Dr Karl-Heinz Heinig, Helmholtz Center Dresden-Rossendorf, Germany

Supervisor:  Professor Hele Savin, Aalto University School of Electrical Engineering, Department of Electronics and Nanoengineering.

Thesis website

Contact information: Zhengjun Liu, Department of Electronics and Nanoengineering, email: [email protected], phone number: +358449350251