We have developed a fabrication scheme for nanoscale devices in silicon using a combination of STM lithography, gaseous precursor dosing, and low-temperature Si growth [1,2]. By patterning a hydrogen resist layer on Si(001) with STM lithography and exposing the surface to phosphine, planar dopant nanostructures can be build. Si encapsulation at low temperatures preserves the dopant pattern and protects the buried device. This technique has the potential to scale down towards single donor devices [3,4]. We have fabricated a number of different nanoscale P dopant devices and investigated their electrical conduction at low-temperatures [5-7]. While previous devices have been patterned in a custom-designed STM-SEM-MBE chamber, we now have successfully transferred the process to a standard Omicron VT-STM equipped with a Si sublimation source for Si growth. An optical microscope is used to position the STM tip with respect to the device area on the sample.
Using this approach, we have fabricated P-doped rings and wires to investigate the phase coherence in electrical conduction at low temperatures. So far, phase coherent transport has been investigated for P δ-doped layers and P-doped nanowires [1,8,9]. In such systems, phase coherence manifests itself in a weak localization peak and negative magnetoresistance at low fields. The phase scattering times and lengths can then be extracted by fitting the shape of the magnetoresistance curves to theory. Here, we present low-temperature magnetotransport measurements for P-doped rings. Such nano-scale interferometers are promising systems to directly observe phase coherence in electrical transport.
[1] F. Rueβ et al., Nano Letters 4, 1969 (2004).
[2] M.Y. Simmons et al., Mol. Sim. 31, 505 (2005).
[3] J.R. Tucker and T.-C. Shen, Solid State Electron. 42, 1061 (1998).
[4] S.R. Schofield et al., Phys. Rev. Lett. 91, 136104 (2003).
[5] F.J. Rueβ et al., Nanotechnology 18, 044023 (2007).
[6] F.J. Rueβ et al., accepted for publication in Small.
[7] W. Pok et al., accepted for publication in IEEE Trans. Nanotechn. (2007).
[8] K.E.J. Goh et al., Phys. Rev. B 73, 035401 (2006).
[9] S. J. Robinson et al., Phys. Rev. B 74, 153311 (2006).
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