Abstract
Over the past two decades, prototype devices for future classical and quantum computing technologies have been fabricated by using scanning tunneling microscopy and hydrogen resist lithography to position phosphorus atoms in silicon with atomic-scale precision. Despite these successes, phosphine remains the only donor precursor molecule to have been demonstrated as compatible with the hydrogen resist lithography technique. The potential benefits of atomic-scale placement of alternative dopant species have, until now, remained unexplored. In this work, we demonstrate the successful fabrication of atomic-scale structures of arsenic-in-silicon. Using a scanning tunneling microscope tip, we pattern a monolayer hydrogen mask to selectively place arsenic atoms on the Si(001) surface using arsine as the precursor molecule. We fully elucidate the surface chemistry and reaction pathways of arsine on Si(001), revealing significant differences to phosphine. We explain how these differences result in enhanced surface immobilization and in-plane confinement of arsenic compared to phosphorus, and a dose-rate independent arsenic saturation density of 0.24 ± 0.04 monolayers. We demonstrate the successful encapsulation of arsenic delta-layers using silicon molecular beam epitaxy, and find electrical characteristics that are competitive with equivalent structures fabricated with phosphorus. Arsenic delta-layers are also found to offer confinement as good as similarly prepared phosphorus layers, while still retaining >80% carrier activation and sheet resistances of <2 kΩ/square. These excellent characteristics of arsenic represent opportunities to enhance existing capabilities of atomic-scale fabrication of dopant structures in silicon, and may be important for three-dimensional devices, where vertical control of the position of device components is critical.
Highlights
Over the past two decades, prototype devices for future classical and quantum computing technologies have been fabricated by using scanning tunneling microscopy and hydrogen resist lithography to position phosphorus atoms in silicon with atomic-scale precision
The atomic-scale control of dopant atoms in silicon using scanning tunneling microscopy (STM) has to date focused on phosphorus donors, which can be introduced into the silicon matrix using the precursor gas, phosphine (PH3)
We have demonstrated the full compatibility of arsine as a precursor gas for the atomic-scale positioning of arsenic donors in silicon using STM-based hydrogen-desorption lithography, and, when combined with low temperature silicon epitaxy, the capability to fabricate buried, atomic-scale, dopant structures in silicon
Summary
Over the past two decades, prototype devices for future classical and quantum computing technologies have been fabricated by using scanning tunneling microscopy and hydrogen resist lithography to position phosphorus atoms in silicon with atomic-scale precision. Energy in silicon (53.76 meV, compared to 45.59 meV for phosphorus),[24] a larger atomic radius (rAs = 115 pm, rP = 100 pm),[25] larger atomic spin−orbit interaction (ZAs = 33, ZP = 15), and a higher nuclear spin value (IAs = 3/2, IP = 1/2) than phosphorus These differing properties present opportunities for atomic-scale device designs with advanced functionality, including quantum computation schemes based on silicon photonic crystal cavities, which would exploit the larger spin− orbit interaction of arsenic,[26] and schemes employing qudits (generalized d-dimensional quantum information units) where the 4-state Zeeman splitting of the arsenic 3/2 nuclear spin could be utilized as a d = 4 qudit.[27,28] In this latter case, while arsenic nuclear spins can in principle be operated as 2state qubits with some added complexities,[29] accessing the higher dimensionality provided by the 3/2 spin could offer advantages over qubit based quantum computation, including simplifications in physical implementations of quantum gate structures,[30] and greater efficiency and breadth of quantum simulations.[31] the ability to position multiple dopant species in silicon with atomic-scale precision should allow independent addressing of each donor species by exploiting the different orbital excitation energies, and could enable principles of device operation such as optically driven silicon-based quantum gates.[32] the ability to control the reaction of arsine (AsH3) with Si(001) using STM hydrogen-desorption lithography, in an analogous manner to phosphine, presents enormously exciting opportunities for atomic-scale electronics. Kipp et al.[33] have studied the adsorption of arsine on
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