THIN-FILM SILICON FORMATION ON FOREIGN SUBSTRATES BY RAPID THERMAL CHEMICAL-VAPOR-DEPOSITION FOR PHOTOVOLTAIC APPLICATION

Polycrystalline silicon thin-film layers were deposited on foreign sub strates such as SiO2, alumina, mullite and graphite, The deposition st udies were carried out in a single-water, horizontal, rapid thermal ch emical vapour phase reactor at temperatures ranging from 900 degrees C to 1250 degrees C at atmospheric pressure. We employed the gas precur sor trichlorosilane and the layers were doped with boron from the dopa nt source trichloroborine rarified in a hydrogen carrier gas. The surf ace structures and grain sizes of the thin films obtained were evaluat ed by Nomarski microscopy and scanning electron microscopy characteriz ation methods, X-ray diffraction analyses were used to determine the p referential crystalline orientations at various operational parameters . Furthermore, electrical properties in terms of Hall mobility and lif etimes of the minority carriers were investigated by means of Van-der- Pauw and photoconductivity decay methods, respectively. Generally, it has been shown that at elevated deposition temperatures maximum grain sizes of 3-20 mu m for 10-mu m thick layers can be found, depending cr itically on the type of the substrate. For polycrystalline silicon dep osited at 1100 degrees C on silicon dioxide, alumina, and graphite sub strates, a preferred crystallographic orientation of (220) was observe d, implying columnar RI ain structures. (C) 1998 John Wiley & Sons, Lt d.