Characterization of interfaces of metal/amorphized (by implantation) Si/c-Si structures

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Abstract
The electrical properties of metal/implanted (amorphous) Si contacts were studied, emphasizing the effects of the doping level, of the metal type, and of the heat treatments applied prior to the metal deposition. The implantation was carried out using 60‐keV Ar+ ions at a dose of 1016 cm−2, and resulted in the formation of a thin (1000‐Å‐thick) amorphous layer on top of the crystalline substrate. The doping level of the implanted Si affected the current‐voltage (I‐V) characteristics of the contacts mainly in the reverse bias (low doping–low currents), while the forward bias characteristics were quite independent of this parameter. The device characteristics were very sensitive to the metal type, Al, Ti‐W, or Pt. Thermal treatments applied prior to the metal deposition affected the characteristics by lowering the device resistance in correspondence with the thinning of the amorphous layer as a result of epitaxial regrowth. The I‐V characteristics, as well as their dependence on the different process parameters, are explained using a model of charge injection into a thin layer of trap rich amorphous Si bounded by a metal/a‐Si interface on one side and by an a‐Si/c‐Si heterojunction on the other side.