Periodic Reporting for period 1 - NANOWHYR (Dots-in-NANOWires by near-field illumination: novel single-photon sources for HYbRid quantum photonic circuits)
Période du rapport: 2022-12-01 au 2025-05-31
Quantum technologies are sparking interest in the science and technology communities all over the world because they enable computation and communication protocols with intrinsically superior performance and security with respect to the classical protocols. Nowadays, there is special focus in the creation of quantum photonic devices for performing these operations, because photons are excellent, low-noise carriers of information.
Integrated quantum photonic circuits enable the chip-scale realization of quantum technologies. In these circuits, non-classical light states (e.g. single photons) are generated, manipulated, and detected on the same platform. However, efficiently integrating these three operations on-chip is a grand challenge, due to the material requirements ideal for the three processes, requirements which are often incompatible with each other. Indeed, on the one hand, solid-state quantum emitters, such as self-assembled III-V quantum dots (QDs), have reached excellent performances as single photon generators. On the other hand, Si-based photonic circuits are unrivaled in integrating thousands of components on chip and in compatibility with electronic and optoelectronic devices.
Along with trying a monolithic growth of high-quality III-V self-assembled QDs on Si, a lot of effort is put in either forcing Si to have a direct bandgap and use it as a photon emitter itself, or improving all III-V-based photonic circuits wherein QDs are grown. Alternatively, an ideal approach is the combination of the two independently optimized systems (III-V QDs and Si circuits) on the same chip, which can be realized with a hybrid post-growth integration of III-V QDs on Si.
Even though a lot of progress has been made in both the monolithic and the hybrid integration, there are still major open challenges, such as the need to control separately each QD, to fine tune the QD position and energy (in view of interfacing multiple identical QDs in a scalable platform), and the need to achieve emission at the so-called telecom wavelengths (e.g. λ⁓1.31 or 1.55 µm), which are desired for fiber-based long-distance networks (and are beneficial for minimizing losses in Si circuits).
Different solutions have been found to solve one or more of these challenges, but it is now timely to develop a unitary approach to solve all of them at once, which is the main aim of this project and can ultimately lead to the ideal Si-based all-inclusive photonic circuit.
Integrated quantum photonic circuits enable the chip-scale realization of quantum technologies. In these circuits, non-classical light states (e.g. single photons) are generated, manipulated, and detected on the same platform. However, efficiently integrating these three operations on-chip is a grand challenge, due to the material requirements ideal for the three processes, requirements which are often incompatible with each other. Indeed, on the one hand, solid-state quantum emitters, such as self-assembled III-V quantum dots (QDs), have reached excellent performances as single photon generators. On the other hand, Si-based photonic circuits are unrivaled in integrating thousands of components on chip and in compatibility with electronic and optoelectronic devices.
Along with trying a monolithic growth of high-quality III-V self-assembled QDs on Si, a lot of effort is put in either forcing Si to have a direct bandgap and use it as a photon emitter itself, or improving all III-V-based photonic circuits wherein QDs are grown. Alternatively, an ideal approach is the combination of the two independently optimized systems (III-V QDs and Si circuits) on the same chip, which can be realized with a hybrid post-growth integration of III-V QDs on Si.
Even though a lot of progress has been made in both the monolithic and the hybrid integration, there are still major open challenges, such as the need to control separately each QD, to fine tune the QD position and energy (in view of interfacing multiple identical QDs in a scalable platform), and the need to achieve emission at the so-called telecom wavelengths (e.g. λ⁓1.31 or 1.55 µm), which are desired for fiber-based long-distance networks (and are beneficial for minimizing losses in Si circuits).
Different solutions have been found to solve one or more of these challenges, but it is now timely to develop a unitary approach to solve all of them at once, which is the main aim of this project and can ultimately lead to the ideal Si-based all-inclusive photonic circuit.
The NANOWHYR project aims at addressing the major challenges currently hampering efficient integration of QDs on Si, by using III-V QDs in semiconductors nanowires (NWs). NWs are rod-shaped semiconductors with diameters of few to dozens of nanometers and length of few micrometers. NWs can host site-controlled III-V QDs ideal for a post-growth integration to Si via pick-and-place techniques, and they can also be directly grown on Si with high quality.
NWs can be grown via a bottom-up, scalable approach. Their density, size, morphology, and chemical compositions can be finely controlled by modern growth techniques. Thanks to the NW capability to release strain at the NW free sidewalls, they can host heterostructures that can hardly be obtained in their planar counterparts. For similar reasons, NWs are typically free from long-range crystalline defects.
However, employing QDs in NWs as single photon sources involves several other challenges (improving tpurity, indistinguishability, efficiency etc.). The solution we propose to solve them is wide-ranging, as it can be implementated in both architectures: the hybrid configuration and the monolithic configuration.
The objectives of the NANOWHYR project are:
• Hybrid integration of a single dot-in-NW on a Si chip. The QD will emit single photons in a broad and tunable range (from near infrared to telecom λ). The chip can contain an artificial cavity, such as a photonic crystal, or a NW waveguide. The formation of the QD takes place via spatially controlled hydrogenation, namely by removing hydrogen via near field illumination or by selective hydrogenation of NW portions.
• Monolithic integration of a single, vertical III-V QD in a NW array, grown on mainstream Si substrates. The QD emits single photons with tunable energies as above. The quantum emitter can be formed via special heterostructure designs, during growth, or via interplay of hydrogenation and hydrogen removal post-growth, and it can be contained in cavities.
The target materials are dilute nitrides like GaAsN and InN. When InN and GaAsN are used, bandgap energy can be fine-tuned by hydrogenation. Alternative material systems, such as GaAsP and InAs-based QDs in NWs, are being investigated when QDs formed during growth are needed, such as to study hydrogen effect on QD intensity, NW waveguiding properties, benchmarking single-photon-emitters formed during growth, obtaining emitters at specific desired energies.
NWs can be grown via a bottom-up, scalable approach. Their density, size, morphology, and chemical compositions can be finely controlled by modern growth techniques. Thanks to the NW capability to release strain at the NW free sidewalls, they can host heterostructures that can hardly be obtained in their planar counterparts. For similar reasons, NWs are typically free from long-range crystalline defects.
However, employing QDs in NWs as single photon sources involves several other challenges (improving tpurity, indistinguishability, efficiency etc.). The solution we propose to solve them is wide-ranging, as it can be implementated in both architectures: the hybrid configuration and the monolithic configuration.
The objectives of the NANOWHYR project are:
• Hybrid integration of a single dot-in-NW on a Si chip. The QD will emit single photons in a broad and tunable range (from near infrared to telecom λ). The chip can contain an artificial cavity, such as a photonic crystal, or a NW waveguide. The formation of the QD takes place via spatially controlled hydrogenation, namely by removing hydrogen via near field illumination or by selective hydrogenation of NW portions.
• Monolithic integration of a single, vertical III-V QD in a NW array, grown on mainstream Si substrates. The QD emits single photons with tunable energies as above. The quantum emitter can be formed via special heterostructure designs, during growth, or via interplay of hydrogenation and hydrogen removal post-growth, and it can be contained in cavities.
The target materials are dilute nitrides like GaAsN and InN. When InN and GaAsN are used, bandgap energy can be fine-tuned by hydrogenation. Alternative material systems, such as GaAsP and InAs-based QDs in NWs, are being investigated when QDs formed during growth are needed, such as to study hydrogen effect on QD intensity, NW waveguiding properties, benchmarking single-photon-emitters formed during growth, obtaining emitters at specific desired energies.
The state of the art in the field of quantum photonic circuits based on NWs is dominated by NWs in which a III-V QD is formed during growth (via conventional hetero-structuring or via crystal phase switching between wurtzite and zincblende). In one of our approaches, instead, the single photon emitter is created after NW growth, for the first time in NWs. This adds important features like energy tunability, position control, and control of the number of quantum emitters without affecting energy and position of the others.
Along with the capability, inherent to NWs, to be integrated in Si chips (post-growth or during growth), our project can lead to the ideal single photon source on Si. By merging the advantages of the single photon sources in III-V NWs with the advances gained in 20 years of research in planar QDs located into cavities and waveguides, NANOWHYR will allow to deterministically place a high-quality single photon source in any desired point of a Si photonic circuit.
In contrast from existing approaches, our quantum emitters can be optimally integrated in prefabricated circuits, as the emitters properties will be tailored to the circuit and not viceversa. The site- and energy-controlled emitters that we want to create in this project can then be the quantum bricks for a variety of quantum photonics architectures.
Moreover, the idea of creating material properties post-growth while monitoring their properties as formed has enormous potential: one can obtain desired properties with no need to start a new, time-consuming, growth process. This concept could be also introduced in other fields that involve difficult semiconductor hetero-structuring. For example, in multi-junction solar cells, obtaining by-growth layers of materials with different bandgaps can be limited by lattice mismatch issues. With this post-growth approach, instead, one could grow just one peculiar material and largely tune its bandgap energy post-growth by our controlled processes. Similarly, this can lead to nanoscale semiconductor hetero-structures that could boost the conversion power of wasted heat into electricity.
Along with the capability, inherent to NWs, to be integrated in Si chips (post-growth or during growth), our project can lead to the ideal single photon source on Si. By merging the advantages of the single photon sources in III-V NWs with the advances gained in 20 years of research in planar QDs located into cavities and waveguides, NANOWHYR will allow to deterministically place a high-quality single photon source in any desired point of a Si photonic circuit.
In contrast from existing approaches, our quantum emitters can be optimally integrated in prefabricated circuits, as the emitters properties will be tailored to the circuit and not viceversa. The site- and energy-controlled emitters that we want to create in this project can then be the quantum bricks for a variety of quantum photonics architectures.
Moreover, the idea of creating material properties post-growth while monitoring their properties as formed has enormous potential: one can obtain desired properties with no need to start a new, time-consuming, growth process. This concept could be also introduced in other fields that involve difficult semiconductor hetero-structuring. For example, in multi-junction solar cells, obtaining by-growth layers of materials with different bandgaps can be limited by lattice mismatch issues. With this post-growth approach, instead, one could grow just one peculiar material and largely tune its bandgap energy post-growth by our controlled processes. Similarly, this can lead to nanoscale semiconductor hetero-structures that could boost the conversion power of wasted heat into electricity.