A Simulation Study for Optimizing Grain Size in Poly-Crystalline Silicon Material Using Impedance Spectroscopy

This paper uses impedance spectroscopy as a simulation tool to analyze grain boundaries properties in poly-crystalline materials. The interfacial structure at grain boundaries in poly-crystalline materials plays a decisive role in their electrical behaviors and degrades the performance in integrated circuits, gas sensors and solar photovoltaics. A numerical simulation is carried out to optimize grain size of poly-crystalline material to behave as mono-like material using impedance spectroscopy technique. The grain boundary potential (Vb) obtained from thermionic emission diffusion theory based continuum and localized energy models are utilized for obtaining the resistance (R), capacitance (C) and angular frequency (??) of the bulk of the grain (Rb, Cb and ??b) and that of grain boundaries (Rgb, Cgb and ??gb) using the brick layer model. Two markedly different impedance spectra are obtained, one for the bulk of the grain and another for the grain boundaries. It is found that with an increase in the grain size (Lg), the signatures of grain boundaries spectra diminish and at a particular grain size, disappear completely which indicates that the poly-silicon material behaves comparable to mono-crystalline material. In this simulation work, silicon material is taken as the reference due to its abundant availability and huge market potential for photovoltaic and semiconductor applications but the simulation can be implemented on any poly-crystalline materials. The effect of varying silicon material resistivity (1.0???3.5 ??cm) and temperature (300-420 K) on grain size was also analysed using the impedance spectra. The findings of the paper will be helpful for the silicon ingot growth industries to decide the optimum grain size during the polysilicon materials growth.