Scalable Nanomanufacturing of Quantum Dot Heterointegrated Nanophotonic Cavities

Nanophotonic structures are a foundation for the emerging field of light-based quantum networks and devices. These nanoscale structures act through their ability to couple with and manipulate photons. Colloidal quantum dots (QDs) are uniquely suited to complement this range of devices due to their solution-processability, broad tuneability, and near-unity photoluminescence quantum yields, in some cases. Here we have used electrohydrodynamic inkjet (EHDIJ) printing as a highly precise and scalable nanomanufacturing method for digital deposition of attoliter-scale QD droplets to bridge the heterointegration gap between QDs and nanophotonics. EHDIJ printing is an electrophoretic additive manufacturing process that uses applied electric fields to overcome surface energy barriers to selectively deposit charged droplets and deterministically position functional materials, including QDs, down to nanoscale resolutions.<br/><br/>For monolithic substrate-coupled SiN nanophotonic cavities, we have shown that CsPbBr₃ QDs can be deterministically patterned over large arrays and with sub-micrometer precision using EHDIJ printing. Additionally, we collected the first high-resolution STEM images of EHDIJ printed structures, showing that the original QD structure is preserved post-printing. Furthermore, we found that QDs within these printed structures can self-assemble into superlattice domains and that ∼200 nm diameter printed features containing ≤200 QDs can be produced with this technique.<br/><br/>Building on this capability, EHDIJ printing has been expanded to encompass heterointegration of structures that are challenging or impossible to create by conventional subtractive semiconductor processing. An example of this is the coupling of QD emitters to substrate-decoupled nanoscale resonant structures. We have demonstrated the first successful application of EHDIJ printing for the integration of colloidal CdSe/CdS QDs with suspended nanophotonic cavities, achieving selective single-cavity deposition for cavity pairs as close as 100 nm apart. PL characterization of the as-printed cavities confirmed EHDIJ printing’s ability to manufacture QD-cavity and inter-cavity coupled devices, at nanoscale spacings. This broadens the horizon for new hybrid integrated device architectures that were previously considered impossible from a materials integration standpoint.<br/><br/>To demonstrate this broad applicability, we have also begun to apply strategies learned from these previous demonstrations onto bullseye cavity structures. These consist of semi-complete suspended concentric rings of alternating dielectrics, SiN and air. Bullseye cavities offer increased Purcell enhancement and the unique ability to direct emission from photon sources into the far field. Using EHDIJ printing, we are integrating CsPbBr₃QDs into 500 nm diameter cavity-centered targets, while tuning the colloidal solution’s concentration and chemistry to minimize the number of QDs integrated into the devices towards single QD and single photon systems.<br/><br/>We believe these results will motivate the development of future suspended heterointegrated devices that utilize EHDIJ printing as a sustainable, additive, and scalable method for quantum photonics nanomanufacturing.