Electronic Instrumentation Laboratory
Department of Microelectronics

Piet Xiaowen Fang

Publications

  1. A doping-less junction-formation mechanism between n-silicon and an atomically thin boron layer
    V. Mohammadi; S. Nihtianov; C. Fang;
    Scientific Reports,
    Volume 7, Issue 1, 2017. cited By 0. DOI: 10.1038/s41598-017-13100-0
    Abstract: ... The interest in nanostructures of silicon and its dopants has significantly increased. We report the creation of an ultimately-shallow junction at the surface of n-type silicon with excellent electrical and optical characteristics made by depositing an atomically thin boron layer at a relatively low temperature where no doping of silicon is expected. The presented experimental results and simulations of the ab initio quantum mechanics molecular dynamics prove that the structure of this new type of junction differs from all other known rectifying junctions at this time. An analysis of the junction formation has led to the conclusion that the chemical interaction between the surface atoms of crystalline silicon and the first atomic layer of the as-deposited amorphous boron is the dominant factor leading to the formation of a depletion zone in the crystalline silicon which originates from the surface. The simulation results show a very strong electric field across the c-Si/a-B interface systems where the charge transfer occurs mainly from the interface Si atoms to the neighboring B atoms. This electric field appears to be responsible for the creation of a depletion zone in the n-silicon resulting in a rectifying junction-formation between the n-silicon and the atomically thin boron layer.

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  2. Stability, local structure and electronic properties of borane radicals on the Si(100) 2x1:H surface: A first-principles study
    C.M. Fang; V. Mohammadi; S. Nihtianov; M.H.F. Sluiter;
    Computational Materials Science,
    Volume 140, Issue Supplement C, pp. 253 - 260, 2017. DOI: https://doi.org/10.1016/j.commatsci.2017.08.036
    Keywords: ... Borane deposition, H passivated Si(001) surface, PureB process, Ab initio calculations.

    Abstract: ... Abstract Deposition of a thin B layer via decomposition of B2H6 on Si (PureB process) produces B-Si junctions which exhibit unique electronic and optical properties. Here we present the results of our systematic first-principles study of BHn (n=0-3) radicals on Si(100)2x1:H surfaces, the initial stage of the PureB process. The calculations reveal an unexpectedly high stability of BH2 and BH3 radicals on the surface and a plausible atomic exchange mechanism of surface Si atoms with B atoms from absorbed BHn radicals. The calculations show strong local structural relaxation and reconstructions, as well as strong chemical bonding between the surface Si and the BHn radicals. Electronic structure calculations show various defect states in the energy gap of Si due to the BHn absorption. These results shed light on the initial stages of the complicated PureB process and also rationalize the unusual electronic, optical and electrical properties of the deposited Si surfaces.

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