In-situ ellipsometric studies on epitaxially grown silicon by hot-wire CVD

Epitaxial growth of undoped silicon at low substrate temperatures (Ts) using the hot-wire chemical vapour deposition (HWCVD) has been studied by in-situ ellipsometry. As expected, it was found that the formation of a crystalline, amorphous or mixed phase mainly depends on Ts, deposition rate (rd) and gas pressure. Using rd=2.0 Å/s the growth of a mixed phase of amorphous and crystalline silicon has been observed where the crystalline volume fraction decreases almost linearly during deposition. By lowering rd down to 1.0 Å/s epitaxial growth can be observed at Ts=300°C without surface roughening and stacking faults yielding to converging ellipsometric trajectories of a c-Si phase. The epitaxial films are found to have a lower-density region near the c-Si/film interface with a void density of a few percent. The microstructure is confirmed by transmission electron microscopy measurements, too. First attempts in growing n-type emitters epitaxially on p-type crystalline silicon by HWCVD have been undertaken. This structure has been included into homojunction solar cells and at the present state of development a conversion efficiency of η=10.8% has been obtained.