INFLUENCE OF THE ADDITION OF CO AND NI ON THE FORMATION OF EPITAXIAL SEMICONDUCTING BETA-FESI2 - COMPARISON OF DIFFERENT EVAPORATION METHODS

beta-FeSi2 films containing 4-25 at. % of Co or Ni have been grown on (111) Si using three different evaporation methods: deposition of the metal film at room temperature followed by solid state reaction (solid phase epitaxy), deposition of the metal on a heated wafer [reactive d eposition epitaxy: (RDE)] codeposition of metal and Si in the stoichio metric proportions [molecular beam epitaxy: (MBE)]. The films have bee n analysed with Rutherford backscattering spectrometry, x-ray diffract ion, secondary ion mass spectroscopy, and scanning electron microscopy . We show that beta-FeSi2 can be obtained with the three methods, howe ver the quality, the epitaxial character and the morphology of the fil ms differ. By far, the best results are obtained by MBE. In that case the codeposition of a Fe(Ni) alloy and Si at 550 degrees C leads to a large, epitaxial, mirror like beta-Fe(Ni)Si-2 layer with a homogeneous Ni concentration. Detailed analysis of the Fe(Ni) and Fe(Co)/Si react ion and comparison with the Fe/Si one shows that: (i) Ni and Co do not modify the temperature of formation and the stability of the differen t Fe silicides providing the solubility limits in the different phases are not exceeded (e.g., 6 and 12 at. % in beta-FeSi2), (ii) the first stages of the reaction are characterized by the formation of a nonhom ogeneous layer of FeSi. We did not observe the formation of a Si solid solution in Fe or of the ordered Fe3Si phase, (iii) the transformatio n from FeSi to beta-FeSi2 induces a degradation of the beta-FeSi2 laye r morphology. This explains why the processes (RDE and MBE) bypassing the formation of FeSi give better epitaxial layers. (C) 1998 American Institute of Physics.