Research

 

Polycrystalline silicon thin films on glass substrates are attractive for large area electronics and solar cell applications. A promising method to obtain large-grained high quality polycrystalline films by crystallization of an amorphous precursor material is the aluminum-induced layer exchange (ALILE). Here, an Al/amorphous Si layer stack, separated by a thin oxide film, is annealed at temperatures below the eutectic temperature of 577 °C, leading to an exchange of the positions of the initial layers and the crystallization of the amorphous Si (see figure below).

 

 

Steps of the ALILE process: (a) Al/amorphous Si layer stack on glass substrate as starting configuration. (b) and (c) During the annealing Si nuclei form in the Al and grow in size. (d) Finally a closed polycrystalline layer has formed replacing the Al.  

 

My research focuses on the electronic properties of polycrystalline Si films prepared by ALILE. Due to the high solubility of Al in Si, the layers are highly p-doped after the exchange process. Their hole carrier concentration is of the order of 10¹⁸ - 10¹⁹ cm^-3, and even higher for very thin samples. For electronic applications, e.g. as solar cell absorber material or in a thin film transistor, such high carrier concentrations are not desirable. A well known method to reduce the carrier concentration of semiconductor materials is the incorporation of hydrogen/deuterium to passivate shallow dopants.

 

Transistor test structures have been processed to learn more about the field effect in the hydrogenated poly-Si layers and their potential for electronic applications. Good results have been obtained with back gate structures on high-k dielectrica with field effect mobilities up to ~20 cm²/Vs. Interface properties are investigated by means of C-V and frequency-dependent conductivity measurements. Further research focuses on Schottky- and pn-diodes composed of the ALILE layers. 

 

Future activities will also include the interdisciplinary field of physical cryptography using electrical approaches.  

 

Publications