Bound states in the continuum (BIC) have attracted a great deal of attention in all-dielectric nanophotonics due to their ability to provide spectral features with a very high-quality factor. By definition, BIC cannot be observed in the far field because of the symmetry mismatch with the modes propagating in free space. Despite this, in systems with slightly reduced symmetry, the condition for BIC is lifted, which gives rise to the high-quality resonant features in their optical response. In particular, in photonic crystal slabs, which support the BIC states, the symmetry reduction allows modification of light propagation, reflection, or emission. In this work, using the photonic crystal slabs with embedded Ge nanoislands, we have shown the ability to control their light emission features by symmetry breaking. It was demonstrated that such symmetry breaking due to a change in the basis vectors of the photonic crystal unit cell or a change in the unit cell internal structure could provide independent control knobs to alter the spectral position of photonic crystal modes, their dispersion, and degeneracy. The obtained results reveal additional ways to manage the light emission of active media in photonic crystal slabs.

Subject of study. This study investigated SiGe heterostructures with self-assembled Ge(Si) nanoislands embedded in two-dimensional photonic crystals. Aim of study. The aim of the study was to determine the dependence of the spectral and temporal characteristics of the radiation of structures with Ge(Si) islands in two-dimensional photonic crystals on the depth of the holes forming the photonic crystal. Additionally, the characteristic decay times of the luminescence of islands in photonic crystals and the main mechanisms influencing their dependence on the etching depth of the photonic-crystal holes were determined. Method. The studied structures were obtained using molecular-beam epitaxy, electron-beam lithography, and plasma-chemical etching. The optical properties of the obtained structures were analyzed using microphotoluminescence spectroscopy with high spectral (0.5 nm) and temporal (50 ps) resolution. Main results. The dependences of the intensity, spectral shape, and characteristic decay times of the photoluminescence of self-assembled Ge(Si) islands in two-dimensional photonic crystals with a hexagonal lattice on the etching depth of the photonic-crystal holes were determined. The characteristic decay time of the luminescence of islands in the photonic crystals at room temperature decreased from 9 ns for the initial structure without photonic crystals to 0.6 ns for the sample with holes etched to the full depth of the grown structure (335 nm). This decrease is associated with an increase in the nonradiative recombination of charge carriers at the hole boundaries. The optimal ratio of the hole depth to the thickness of the active region of the structure was determined. Using this optimal ratio led to a maximum increase in the luminescence intensity of the Ge(Si) islands in two-dimensional photonic crystals compared with that of planar structures without photonic crystals. Practical significance. The obtained results are important for the development of efficient light sources in the near-infrared range for silicon-based integrated optoelectronics. (c) 2025 Optica Publishing Group

The effects of resonance interaction of plasmonic and photonic modes in hybrid metal-dielectric structures with square Al nanodisk lattices coupled with a Si waveguide layer were investigated using micro-photoluminescence (micro-PL) spectroscopy. As radiation sources, GeSi quantum dots were embedded in the waveguide. A set of narrow PL peaks superimposed on the broad bands were observed in the range of quantum dot emissions. At optimal parameters of Al nanodisks lattices, almost one order increasing of PL intensity was obtained. The experimental PL spectra are in good agreement with results of theoretical calculations. The realization of high-quality bound states in the continuum was confirmed by a comparative analysis of the experimental spectra and theoretical dispersion dependences. The results demonstrated the perspectives of these type structures for a flat band realization and supporting the slow light.

In this paper, we study the emission spectrum of the photonic crystal slab (PCS) with embedded Ge/Si quantum dots using the original technique of a directional micro-photoluminescence (DPL). This technique is a powerful combination of two approaches to the experimental study of PCS. First, it allows to collect photoluminescence (PL) signal within small solid angles in the selected directions and thereby to study the dispersion dependence of PCS modes. Second, it gives the experimental opportunity to analyze the quality-factor change of observed PL peaks with an increase in the collection angle and allows us to find in the PL spectrum the high-quality modes, namely the bound states in the continuum. A comparison with theoretical dispersion dependencies of PCS modes calculated by the Fourier-modal method in the scattering matrix form demonstrates a clear correspondence between PCS dispersion curves and angular dependencies of observed PL peak positions. The obtained results indicate that the DPL technique can be successfully used both to visualize the photonic band structure and to determine the nature of the PCS modes.

The effect of optical excitation conditions on the spectral and temporal characteristics of the radiation from two-dimensional photonic crystals based on the structures with self-assembled Ge(Si) nanoislands has been studied. It was shown that one of the main factors effecting the spectral position and shape of photoluminescence lines, as well as the photoluminescence kinetics of photonic crystals with Ge(Si) nanoislands, along with the mode structure of the photonic crystal, are the local heating of the samples and the concentration of nonequilibrium charge carriers created by the absorption of the pumping radiation.

Detailed studies of the luminescent properties of the Si-based 2D photonic crystal (PhC) slabs with air holes of various depths are reported. Ge self-assembled quantum dots served as an internal light source. It was obtained that changing the air hole depth is a powerful tool which allows tuning of the optical properties of the PhC. It was shown that increasing the depth of the holes in the PhC has complex influences on its overall photoluminescence (PL) response due to the simultaneous influences of counteracting factors. As a result, the maximal increase in the PL signal of more than two orders of magnitude was obtained for some intermediate, but not full, depth of the PhC's air holes. It was demonstrated that it is possible to engineer the PhC band structure in such a way as to construct specific states, namely bound states in continuum (BIC), with specially designed dispersion curves being relatively flat. In this case, such states manifest themselves as sharp peaks in the PL spectra, and have high Q-factors which are larger than those of radiative modes and other BIC modes without such a flat dispersion characteristic.

The interaction of Ge(Si)/SOI self-assembled nanoislands with modes of photonic crystal slabs (PCS) with a hexagonal lattice is studied in detail. Appropriate selection of the PCS parameters and conditions for collecting the photoluminescence (PL) signal allowed to distinguish the PCS modes of different physical nature, particularly the radiative modes and modes associated to the bound states in the continuum (BIC). It is shown that the radiative modes with relatively low Q-factors could provide a increase greater than an order of magnitude in the integrated PL intensity in the wavelength range of 1.3–1.55 µm compared to the area outside of PCS at room temperature. At the same time, the interaction of Ge(Si) islands emission with the BIC-related modes provides the peak PL intensity increase of more than two orders of magnitude. The experimentally measured Q-factor of the PL line associated with the symmetry-protected BIC mode reaches the value of 2600.

In this work, we investigated the luminescent properties of two-dimensional photonic crystals (PhCs) with ordered Ge(Si) nanoislands obtained using one-and two-stage approaches to ordering. The features of the luminescent response of such structures and their relationship with the ordering processes of nanoislands are considered. It is shown that the incorporation of Ge(Si) nanoislands into a two-dimensional PhC makes it possible to increase the intensity of their luminescent response by more than an order of magnitude, which makes the structures under consideration promising for practical applications.

The results of studying the luminescent properties of epitaxially grown structures with spatially ordered Ge/Si nanoislands (quantum dots), in which the pit-patterned “silicon-on-insulator” substrates serve both for the spatial ordering of quantum dots and for the two-dimensional photonic crystal formation, are presented. It is found that with a certain choice of pit-patterned substrate parameters (diameter of pits and their spatial period), in the photoluminescence spectra of such structures, the multiple narrow peaks are observed. In addition, a significant increase in the quantum dot luminescence signal intensity occurs in the near-infrared range. The effects are related to resonance interaction of quantum dot emitters with photonic crystal modes. The luminescence enhancement effect persists up to room temperatures.

This paper presents the results of studies of the luminescence properties of structures with Ge(Si) quantum dots (QDs), in which the pit-patterned surface of a silicon-on-insulator substrate serves both for the spatial ordering of QDs and the formation of a two-dimensional photonic crystal. It is shown that by choosing the parameters of the pit-patterned substrate (the diameter of the pits and the period of their location), it is possible to provide a significant increase in the intensity of the QD luminescence signal in the near infrared range. This enhancement is associated with the interaction of spatially ordered QD emission with the modes of a photonic crystal formed by the pattern of pits. The effect of amplification of the luminescence signal is retained up to room temperature.

This paper presents the results of studies of the luminescence properties of structures with Ge(Si) quantum dots (QDs), in which a pit-patterned surface of silicon on insulator substrate served both for the spatial ordering of QDs and for the formation of a two-dimensional photonic crystal. It is shown that by choosing the parameters of pit-patterned substrate (the diameter of the pits and the period of their location), it is possible to provide a significant increase of intensity of the QD luminescence signal in the near-IR range. This enhancement is associated with interaction of spatially ordered QD emission with the modes of a photonic crystal formed by the pattern of pits. The effect of amplification of the luminescence signal persists up to room temperature.

A new approach to improve the light-emitting efficiency of Ge(Si) quantum dots (QDs) by the formation of an ordered array of QDs on a pit-patterned silicon-on-insulator (SOI) substrate is presented. This approach makes it possible to use the same pre-patterned substrate both for the growth of spatially ordered QDs and for the formation of photonic crystal (PhC) in which QDs are embedded. The periodic array of deep pits on the SOI substrate simultaneously serves as a template for spatially ordering of QDs and the basis for two-dimensional PhCs. As a result of theoretical and experimental studies, the main regularities of the QD nucleation on the pre-patterned surface with deep pits were revealed. The parameters of the pit-patterned substrate (the period of the location of the pits, the pit shape, and depth) providing a significant increase of the QD luminescence intensity due to the effective interaction of QD emission with the PhC modes are found.

Photoluminescence (PL) properties of arrays of spatially ordered single Ge(Si) self-assembled islands, including embedded in two-dimensional photonic crystals (PhC), was studied. Incorporation of an array of ordered single islands and their groups into PhC significantly increases the intensity of their PL signal. The most pronounced increase in intensity (up to 30 times at nitrogen temperatures) is observed for an ordered array of single islands. The increase in PL intensity is associated with interaction of island emission with the radiation modes of the PhC, which is more efficient for an array of spatially ordered single islands. As result PL from single ordered Ge(Si) islands embedded in PhC was observed up to room temperature.