Precision few-electron silicon quantum dots
2011Supervisor:
Thesis: PhD (2011)- Published: 2011
URN/HDL:
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Abstract: (New South Wales U.)
We demonstrate the successful down-scaling of donor-based silicon quantum dot structures to the single donor limit. These planar devices are realized in ultra high vacuum (UHV) by means of scanning tunneling microscope (STM) based hydrogen lithography which – in combination with a gaseous dopant source and a thermal silicon source – allows for the
patterning of highly-doped planar Si:P structures with sub-nm precision encapsulated in a single-crystal environment.
We present advancements of the alignment strategy for patterning ex-situ metallic contacts and top gates over the buried dopant devices. Here, we use a hierarchical array of etched registration markers. A key feature of the alignment process is the controlled formation of atomically flat plateaus several hundred nanometers in diameter that allows the active region of the device to be patterned on a single atomic Si(100) plane at a precisely known
position.
We present a multiterminal Si:P quantum dot device in the many-electron regime. Coplanar regions of highly doped silicon are used to gate the quantum dot potential resulting in highly stable Coulomb blockade oscillations. We compare the use of these all epitaxial in-plane gates with conventional metallic surface gates and find superior stability of the former.
We highlight the challenges of down-scaling within a planar architecture and show how capacitance modeling can be used to optimize the tunability of quantum dot devices. Based on these results, we demonstrate the fabrication of an in-plane gated few-donor quantum dot device which shows highly stable Coulomb blockade oscillations as well as a surprisingly dense excitation spectrum on the scale of 100 μeV. We explain how these low energy resonances arise from transport through valley-split states of the silicon quantum dot providing extensive effective mass calculations to support our findings.
Finally, we describe how STM H-lithography can be used to incorporate individual impurities at precisely known positions within a gated device and demonstrate transport through a single phosphorus donor. We find a bulk-like charging energy as well as clear indications for bulk-like excited states. We highlight the potential of this technology to realize elementary building blocks for future donor-based quantum computation applications in silicon.- Silicon
- Scanning tunneling microscope
- Quantum dots
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