Mariia Lamers

My research is about the epitaxy of III-V materials for photovoltaic applications. In particular, I work on nanowire multijunction solar cells. Multijunction means each nanowire (NW) has a combination of two or more p-i-n junctions that one finds in solar cells. These structures have the potential to be more efficient than their planar counterparts due to the efficient use of material (10 times less than in planar III-V solar cells).

The material systems I work with are GaAs, GaP, InP, InAs, and heterostructures of those. To characterize samples various tools are used. First, to study electrostatic potential in the nanowire, an electron beam-induced current (EBIC) is used. This is an advanced setup inside scanning electron microscope that consists of a probe with needle that can contact single NW and send electron beam to each point of it. The current that is measured gives a lot of information about grown structures thus creating a very quick and informative feedback loop to growth. With EBIC one does not need to do full processing to measure solar cell characteristics and derive conclusions about the material that was grown. This way one can adjust growth parameters after EBIC measurement to optimize the NW. Other tools are scanning electron microscope (SEM), x-ray diffraction (XRD) to get the composition of heterostructures, external quantum efficiency (EQE) setup, and solar simulator for IV measurements and solar cell characterization, etc.

A few possible applications that can be implemented soon are flexible electronics (for the size of nanowires is small and one can embed them into a flexible polymer). Another one – is solar cells for space (i.e. on satellites). Again, due to the lightweight and radiation hardness of III-V materials.