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Deterministic coupling between SITE-controlled, dilute nitride-based LighT Emitters and tailor-made photonic-crystal structures

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Quantum optical devices

Photonic crystals (PhCs) are periodic optical structures that confine or control the emission and propagation of light. Scientists have developed a way to place individual quantum dots (QDs) in them for exciting new applications in photonics.

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Confining photons has important applications in laser and light-emitting diode technologies because spontaneous emission in microcavities can be greatly enhanced compared to that in free space. The phenomenon can also be exploited in telecommunications and memory devices, and even in sensors for biomedicine. Controlled placement of nano-emitters such as QDs in PhC cavities could provide an approach to real-time, ultrafast control of radiative processes, including spontaneous emission. It is expected to propel the field of nanophotonics, paving the way to realisation of complex photonic circuits, including PhC routers, switches and delay lines. EU-funded scientists exploited new methods for fabrication of site-controlled nano-emitters and PhC cavities through work on the project SITELITE. The final goal is integration of the PhC structures with the light emitters. The first step was to optimise the process for producing site-controlled nano-emitters via spatially selective hydrogenation of dilute nitride semiconductor materials. Dilute nitrides have unique properties distinct from those of conventional semiconductors, including a strong dependence of the band gap on nitrogen content, making them important in applications from long-wavelength optoelectronics to photonics. Researchers improved the properties of QDs fabricated by the process, also called in-plane band gap engineering, achieving single-photon emission. A simplified one-step application process now yields a finished mask immediately after electron-beam lithography, and facilitates a significant increase in successfully processed samples. Further investigations on strain properties modulated by spatially selective hydrogenation of dilute nitrides point the way to control of polarization extent and direction of wire-like structures. This was accomplished via the creation of a strongly anisotropic H-induced strain field in the plane of the sample. The same approach is under development for the realization of tailor-made X-ray photonic structures. Scientists then developed a simple, knowledge-based method for design of PhC cavities, eliminating the trial-and-error procedures currently hindering optimisation and further development. Fabrication of the first set of passive PhC devices is near completion and a series of ordered QD arrays ready for integration is currently undergoing detailed spectroscopic measurements. SITELITE outcomes have been published in major peer-reviewed scientific journals. Placing single quantum objects at arbitrary points of a PhC structure promises to usher in a new era of photonic devices. Potential applications in fields from optoelectronics to biomedicine to energy abound.

Keywords

Photonic crystals, quantum dots, nano-emitters, cavities, dilute nitride

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