Abstract
Site-controlled epitaxial growth of InAs quantum dots on GaAs substrates patterned with periodic nanohole arrays relies on the deterministic nucleation of dots into the holes. In the ideal situation, each hole should be occupied exactly by one single dot, with no nucleation onto planar areas. However, the single-dot occupancy per hole is often made difficult by the fact that lithographically-defined holes are generally much larger than the dots, thus providing several nucleation sites per hole. In addition, deposition of a thin GaAs buffer before the dots tends to further widen the holes in the [110] direction. We have explored a method of native surface oxide removal by using indium beams, which effectively prevents hole elongation along [110] and greatly helps single-dot occupancy per hole. Furthermore, as compared to Ga-assisted deoxidation, In-assisted deoxidation is efficient in completely removing surface contaminants, and any excess In can be easily re-desorbed thermally, thus leaving a clean, smooth GaAs surface. Low temperature photoluminescence showed that inhomogeneous broadening is substantially reduced for QDs grown on In-deoxidized patterns, with respect to planar self-assembled dots.
Highlights
The use of self-assembled quantum dots (QDs) has been suggested as a promising approach in applications as building blocks in single-photon sources and novel quantum computer architectures [1,2].Such applications would greatly benefit from a spectral and spatial control of QDs [3]
In the most studied system, site-controlled InAs/GaAs QDs grown by Molecular Beam Epitaxy (MBE), a critical step is the deoxidation process of the patterned substrate: in order to preserve the hole arrays and to achieve a high surface flatness, thermal deoxidation is preferably replaced by a controlled exposure of the surface to atomic beams at lower temperature, which transforms surface oxides into volatile species
Such alternative procedures must effectively remove surface contaminants, since only thin GaAs buffer layers can be grown before the QD arrays, to avoid planarization of the hole profile
Summary
The use of self-assembled quantum dots (QDs) has been suggested as a promising approach in applications as building blocks in single-photon sources and novel quantum computer architectures [1,2].Such applications would greatly benefit from a spectral and spatial control of QDs [3]. In the most studied system, site-controlled InAs/GaAs QDs grown by Molecular Beam Epitaxy (MBE), a critical step is the deoxidation process of the patterned substrate: in order to preserve the hole arrays and to achieve a high surface flatness, thermal deoxidation is preferably replaced by a controlled exposure of the surface to atomic beams at lower temperature, which transforms surface oxides into volatile species. Such alternative procedures must effectively remove surface contaminants, since only thin GaAs buffer layers can be grown before the QD arrays, to avoid planarization of the hole profile.
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