Towards the Routine Fabrication of P in Si Nanostructures: Understanding P Precursor Molecules on Si(001)
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Towards the routine fabrication of P in Si nanostructures: Understanding P precursor molecules on Si(001) Steven R. Schofield,1,2 Neil J. Curson,2 Oliver Warschkow,3 Nigel A. Marks,3 Hugh F. Wilson,3 Michelle Y. Simmons,2 Phillip V. Smith,1 Marian W. Radny,1 and David R. McKenzie,3 1 School of Mathematical and Physical Sciences, University of Newcastle, Callaghan 2308, Australia 2 Centre for Quantum Computer Technology, School of Physics, University of New South Wales, Sydney 2052, Australia 3 School of Physics, University of Sydney, Sydney 2006, Australia ∗
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ABSTRACT The ability to controllably position individual phosphorus dopant atoms in silicon surfaces is a critical first step in creating nanoscale electronic devices in silicon, for example a phosphorus in silicon quantum computer. While individual P atom placement in Si(001) has been achieved, the ability to routinely position P atoms in Si for large-scale device fabrication requires a more detailed understanding of the physical and chemical processes leading to P atom incorporation. Here we present an atomic-resolution scanning tunneling microscopy study of the interaction of the P precursor molecule phosphine (PH3 ) with the Si(001) surface. In particular, we present the direct observation of PH3 dissociation and diffusion on Si(001) at room temperature and show that this dissociation is occasionally complete, leaving a P monomer bound to the surface. Such surface bound P monomers are important because they are the most likely entry point for P atoms to incorporate into the substrate surface at elevated temperature. INTRODUCTION It has recently been demonstrated that it is possible to controllably position individual P dopant atoms into silicon substrates using a scanning tunneling microscopy based technique [1]. This ability to control the position of dopant atoms in semiconductors with atomic-scale precision has great potential for the creation of atomic-scale electronic devices, for example a silicon-based quantum computer [2]. However, the development of routine methods for positioning individual dopant atoms requires a precise knowledge of the physics and chemistry of each of the stages in the fabrication strategy. Recent first-principles calculations and scanning tunneling microscopy (STM) observations [3] have revealed that the interaction of the P precursor molecule phosphine (PH3 ) with the technologically important silicon (001) surface is much more complex than previously thought [4, and references therein]. Here we present atomic-resolution STM observations of the dissociation and diffusion of PH3 on Si(001). We show that the mechanisms for dissociation and diffusion of PH3 on Si(001) are closely related and that dissociation may sometimes proceed to the point where completely H-free P monomers are bound on top of the substrate surface. Such surface bound P monomers are important because they are the most likely entry point for P atoms
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to incorporate into the substrate surface. The det
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