Growth and characterization of superconducting V3Si on Si and Al2O3 by molecular beam epitaxial techniques

A study of the growth parameters governing the nucleation of metastable superconducting A15 V₃Si on Si and A1₂O₃ is presented. Nominally, 500Å films of V_1-xSi_x were produced through codeposition of V and Si onto heated (111) Si and (1102) A1₂O₃ substrates. Samples were prepared in a custom-built ultrahigh vacuum (UHV) chamber containing dual e-beam evaporation sources and a high temperature substrate heater. V and Si fluxes were adjusted to result in the desired average film composition. V_0.75Si_0.25 films prepared at temperatures in excess of 550° C on Si show significant reaction with the substrate and are nonsuperconducting while similar films grown on A1₂O₃ exhibit superconducting transition temperatures(@#@ T_c @#@) approaching bulk values for V₃Si (16.6-17.1 K). Codeposition at temperatures between 350 and 550° C results in superconducting films on Si substrates while growth at lower temperatures results in nonsuperconducting films. Lowering the growth temperature to 400° C has been shown throughex situ transmission electron microscopy (TEM) and Auger compositional profiling to minimize the reaction with the Si substrate while still activating the surface migration processes needed to nucleate A15 V₃Si. Variation of film composition aboutx = 0.25 is shown to result in nonsuperconducting films for highx and superconducting films with T_c approaching the bulk V value (5.4 K) for lowx. Finally, lowering the V_0.75Si_0.25 deposition rate is shown to raise T_c.