Dr. rer. nat. Moshe Weizman

For his Ph.D thesis the physicist explored the properties of laser-crystallized polycrystalline silicon-germanium (SiGe) layers for thin film solar cells

Born on Febuary 9, 1976 in Jerusalem he received his B.Sc in physics from the Hebrew University at Jerusalem, and wrote his Diploma thesis at the TU Berlin. A scholarship from the Deutsche Bundesstiftung Umwelt made it possible for him to obtain his Ph.D degree from the TU Berlin.

The experimental research for his Ph.D thesis was performed at the Hahn-Meitner-Institut Berlin, now renamed Helmholtz-Zentrum Berlin für Materialien und Energie, under the guidance of Dr. Norbert H. Nickel. In this study he explored the properties of laser-crystallized polycrystalline silicon-germanium (SiGe) layers for thin film solar cells. His thesis, which was highly evaluated by the Fakultät II, Mathematik und Naturwissenschaften of the TU Berlin, has been proposed for the Adlershof Dissertation Prize of 2008.

At present he is leading a project for further development of thin film solar cells involving industry and the Helmholtz-Zentrum Berlin für Materialien und Energie.

His research topic:

Polycrystalline silicon-germanium (SiGe) alloys are a promising material for thin film solar cells. An elegant way to produce polycrystalline SiGe layers is by UV laser irradiation. In the framework of Dr. Weizman’s thesis, such layers were prepared and investigated by a number of characterization methods. Among others, the methods used were: scanning electron microscopy (SEM), atomic force microscopy (AFM), energy dispersive X-ray (EDX), photo-thermal deflection spectroscopy (PDS), electron spin resonance (ESR), in situ transient conductance (TRC) and Hall effect measurements.

In this study it was shown that laser crystallization of SiGe causes the appearance of two astonishing phenomena. First, laser crystallization of SiGe with a germanium content between 30% and 70% results in a self-organized pattern of hillocks or ripples on the surface of the film. This process occurs within 100 ns. The topographic structure exhibits a well defined periodicity length, which is directly coupled to a periodic compositional variation. Second, many of the laser-crystallized poly-SiGe films exhibit high electric conductivity that is several orders of magnitude larger than for pure laser-crystallized Si.

The discovery of these effects, the identification of their origin, and the possibility of controlling them technically opens a new perspective on the utilization of laser-crystallized poly-SiGe alloys for novel large area electronic devices such as thin film solar cells and field emission displays.

Contact: e-mail: weizmann(at)helmholtz-berlin.de