Monash University Research Seminar September 2016
Spatial Metrology of Dopants in Silicon with Exact Lattice Site Precision
Dr. Muhammad Usman
Centre for Quantum Computation and
Communication Technology, School of Physics
The University of Melbourne, Parkville
3010 VIC Australia
Shallow dopants in silicon are promising
candidates for the implementation of spin qubits and quantum logic gates. Excellent
progress in the last few years such as minutes-long coherence time [1], atomically
precise fabrication technique [2], and surface code based architecture scheme
[3] has brought silicon-donor based quantum computers much closer to reality. One
of the key challenges in silicon based quantum computing is to find exact
dopant positions after the fabrication and overgrowth processes, which would greatly
help in the design and optimisation of highly precise quantum logic gates – a
key ingredient for quantum error correction and scale up.
Here we present an
atomically precise metrology based on low temperature STM measurements [4] in
conjunction with a fully quantum, large-volume treatment of the STM-dopant
system [5], which demonstrates the pinpointing of the position of subsurface
phosphorous (P) and arsenic (As) dopants in silicon down to individual lattice
sites.
The STM based metrology technique requires
atomic scale understanding of the measured dopant images with quantitative
precision. To solve this challenging problem, we establish a theoretical
framework by coupling the Bardeen’s tunnelling theory [6] with the atomistic tight-binding
simulations [7] of donor wave function in silicon, which reproduce the STM
images of subsurface dopant wave functions with an unprecedented accuracy. Based
on high-level understanding of STM images and their systematic analysis, we
discover unique patterns of image features, which are highly sensitive to the
3D positioning of the donor underneath the Si surface. Quantitative agreement
between the measured and computed images provides a clear identification of the
exact 3D location of both P and As donors in the Si lattice, down to depths of 5
nm below the Si surface [5]. The established exact donor position metrology will
transform our knowledge of devices and dopant physics at the most fundamental
scale leading to devices with optimised functionality, both in quantum and
classical application.
References:
[1] K Saeedi
et al., Science 342, 830, 2013
[2] B. Weber et al., Science 335,
64, 2012
[3] C. Hill et al., Science Adv.
1, e1500707, 2015
[4] J. Salfi et al., Nature
Materials 13, 605, 2014
[5] M. Usman et al., Nature
Nanotechnology 11, 763, 2016
[6] J. Bardeen PRL 6, 57, 1966
[7] M. Usman et al., Phys. Rev.
B. 91, 245209, 2015