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

Epitaxial growth of undoped silicon at low substrate temperatures (T-s) 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 T-s, deposition rate (r(d)) and gas pressure. Using r(d) = 2.0 Angstrom /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 r(d) down to 1.0 Angstrom /s epitaxial growth can be observed at T-s = 300 degreesC 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 eta = 10.8% has been obtained. (C) 2000 Elsevier Science Ltd. All rights reserved.