Understanding the Growth of β-FeSi[sub 2] Films for Photovoltaic Applications: A Study Using Transmission Electron Microscopy

The microstructure of β-FeSi 2 films grown on Si using magnetron sputtering has been examined using various electron microscopy techniques. After annealing, the differences in interfacial roughness and grain size with different target materials are investigated using secondary electron and transmission electron microscopy techniques. Here, we study the variation in microstructures with sputtered materials. We observed, for Fe sputtered onto Si followed by rapid thermal anneal, the formation of nanosized FeSi 2 grains (∼120 nm) with a rough surface and film/Si interface. These morphologies and microstructure are very different when FeSi 2 is sputtered onto Si and annealed; instead, the formation of micrometer FeSi 2 grains (∼1 to 5 μm) with sharp surfaces and interfaces is observed. In addition, the effect of oxygen on the growth of FeSi 2 has also been studied. Our results show that oxygen impurities in the films result in the formation of Si x O y nanoparticles in the FeSi 2 matrix upon anneal.