Studer, P.R.; (2011) Single donors in silicon for atomic scale devices. Doctoral thesis , UCL (University College London).

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Abstract

This thesis describes a detailed characterization of the atomic scale properties of individual donor atoms in silicon. A cross sectional sample preparation technique was developed, allowing us to study cleaved silicon surfaces using scanning tunnelling microscopy (STM). The Si(111)-2x1 surface is characterized and in particular the properties of anti phase boundaries are investigated. We identify a strain induced band shift associated with the boundaries and furthermore show that they can be controllably manipulated, making them an ideal model system to study and control strain in silicon at the atomic scale. To enable the characterization of individual deep dopants such as bismuth (Bi), which are not used in semiconductor industry, a novel STM sample preparation method was developed. We demonstrate that ion implantation can be used to produce almost defect free samples with high Bi concentrations, suitable for STM measurements. Using cross sectional STM we are furthermore able to laterally resolve the implanted dopant profile and visualize its influence on the band structure of the silicon host crystal. The new sample preparation method is used to investigate the fundamental properties of different group V dopants at the atomic scale. We identify individual bismuth and antimony donors in the Si(111)-2x1 surface and show that their large dopant cores not only induce new atomic reconstructions but also influence the measured charge states. Using scanning tunnelling spectroscopy we furthermore resolve the Coulomb potential well of individual dopants and characterize the influence of surface states on charge screening at the atomic scale. In addition to the described STM work, a state of the art cleanroom fabrication process was developed to allow the placement of individual dopants in silicon with atomic scale precision. This will enable the use of the insights gained about individual donors in this thesis for the fabrication of future single dopant devices.

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