Electrical and structural properties of the Si/C interface in poly-Si thin films on graphite substrates [for PV cells]

For the first time the Si/C interface in poly-Si photovoltaic thin films on graphite substrate is described. The isostatically pressed graphite is covered with a 3-5 μm thick amorphous silicon layer which is recrystallized by the ZMR method (zone melting recrystallization by means of a line electron beam). During ZMR the molten silicon penetrates into the graphite pores, while at the interface β-SiC particles with a size of 50-1000 nm were formed (TEM, SEM analysis). Furthermore there exists a “reaction zone” where Si, SiC and C are found by electron diffraction. As a consequence the poly-Si layer shows an excellent adhesion to the substrate. Since there is no continuous electrically insulating SiC layer formed, highly boron doped seed layers show an ohmic contact to the graphite. The investigated poly-Si thin films on graphite substrate offer a great potential for photovoltaic application after epitaxy up to 50 μm by LPE or CVD