Formation and thermal stability of 2D ordered SiC/Si(001) nanodots
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Dongyue Yang and Jeremy Levy Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, Pennsylvania 15260
Jerrold A. Floro Department of Materials Science and Engineering, University of Virginia, Charlottesville, Virginia 22904 (Received 7 June 2012; accepted 23 October 2012)
Precise spatial ordering of quantum dots (QDs) may enable predictable quantum states due to direct exchange interactions of confined carriers. The realization of predictable quantum states may lead to unique functionalities such as spin cluster qubits and spintronic band gap systems. To define exemplary quantum architectures, one must develop control over QD size and spatial arrangement on the sub-35-nm length scale. We use fine-probe electron beam irradiation to locally decompose ambient hydrocarbons onto a bare Si(001) surface. These carbonaceous patterns are annealed in ultrahigh vacuum (UHV), forming ordered arrays of nanoscale SiC QDs. We have achieved sub-10-nm diameter epitaxially oriented 3C-SiC nanodots with interdot spacings down to 22.5 nm. We investigate the templated feature evolution during UHV annealing and subsequent Ge epitaxial overgrowth to identify key mechanisms that must be controlled to preserve pattern fidelity and reduce broadening of the nanodot distribution.
I. INTRODUCTION
The ability to control the spatial positioning and size distribution of arrays of quantum dots (QDs) would provide an enabling technology for new device paradigms based on interactions between dots that localize charge, spin, or magnetic moment. As an example, relevant to this work, antiferromagnetic coupling with linear chains consisting of an odd number of QDs that each contain a single spin would act as a S 5 ½ cluster qubit, whose behavior closely resembles that of a standard single spin s 5 ½ qubit.1,2 The advantages of a spin cluster qubit are reduced sensitivity to the individual coupling components within the cluster and larger spatial extent of the qubit wave function. This allows one to control the strength of spin coupling within an entire cluster via localized applied magnetic fields on the scale of the entire group, i.e., about an order of magnitude increase in length scale for a 9 spin linear cluster. Well-defined qubits can also be formed from two- or three-dimensional spin clusters with an uncompensated spin.1,2 A key requirement for such arrays or devices is to position spins sufficiently closely to realize exchange coupling energies comparable to kBT. Pryor et al.3 predicted observable exchange coupling behavior between electrons localized by adjacent heteroepitaxial Ge QDs embedded in Si. a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2012.406 J. Mater. Res., Vol. 28, No. 2, Jan 28, 2013
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Strain-induced bending at the band edges of Ge and Si led to formation of shallow minima in the Si conduction band at the heterointerfaces that could confine electrons. The wave function decay lengths are of order 10 nm, allowing an
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