Tip-Enhanced Raman Scattering (TERS) is a powerful method for studying the local properties of nanomaterials. In the gap-mode TERS configuration, the object of investigation is placed in the gap between a TERS probe and a plasmonic nanostructure, it is possible to reach a dramatic increase in Raman sensitivity by choosing the excitation wavelength and plasmonic substrate. Here, we investigate the effect of the excitation wavelength on the TERS response from CdSe nanocrystals on a single Au nanodisk using the gap-mode TERS. For excitation wavelengths of 638.2 and 785.3 nm, the gap-mode TERS by CdSe phonon modes is significantly enhanced at nanodisk edges, forming a ring-like TERS pattern. The diameter of the TERS ring obtained for 638.2 nm amounts to 130 nm. In case of 785.3 nm, the TERS ring diameter increases up to 150 nm that corresponds to the Au nanodisk diameter, while the TERS signal is 12 times stronger than that for 638.2 nm. The calculation results of the near-field scattering from the hot spot, arising between the TERS probe apex and the Au nanodisk covered with a thin CdSe film, using the Finite-Difference Time-Domain method, explain the influence of the excitation wavelength on the TERS pattern variation.

A strong response of nanosystems to the action of weak microwave power through the gap between the sample and the end of the coaxial cable from the microwave generator is detected by measurements at 4.2 K of the conductance of a short-channel p -type silicon transistor and samples with a short quantum point contact in a two-dimensional electron gas of GaAs/AlGaAs heterostructures. The conductance response is gigantic in the tunnel mode of the devices, and the sign of the microwave photoconductance outside this mode depended on the mesoscopic state of the sample and the studied range of gate voltage. The nature of the discovered effects is elucidated by modeling mesoscopic transport within the framework of single-particle quantum mechanics and the Landauer formula as well as by analyzing the basic circuits of electrical control of the semiconductor device. The main reason for the response of nanosystems to microwave exposure is forced in-phase charge oscillations in contacts to the semiconductor due to capacitive coupling in the near metallic environment of the sample.

Quantum point contacts with a short (100-nm) channel in a high-mobility two-dimensional electron gas of GaAs/Al(Ga)As heterostructures and a short-channel p-type field-effect transistor in a silicon-on-insulator structure were fabricated and studied experimentally and by modeling at the Rzhanov Institute of Semiconductor Physics, Siberian Branch, Russian Academy of Sciences, Novosibirsk, Russia, in order to study the response of the samples to weak irradiation by an electromagnetic field with a frequency of 2 GHz. This response in the tunneling mode at a temperature of 4.2 K turned out to be giant and was observed against the background of features caused by impurity disorder.

The continuous scaling of electronic devices leads to the necessity of controlling the structure of low-dimensional materials. Surface-enhanced Raman spectroscopy (SERS) is the technique of choice for studying the crystallinity, composition, and mechanical properties of nanomaterials. Surface-enhanced Raman scattering (SERS) utilizes the electromagnetic field generated by localized surface plasmon resonances (LSPR) in metal nanostructures to enhance the optical response from the sample. Previously the SERS activity of graphene placed on a substrate with an array of gold nanodisks was demonstrated and the enhancement of the main vibrational modes up to 50 times was achieved. Taking into account these results an approach for further improvement of the technique is suggested. It is known that SERS enhancement factor (EF) is dependent on the gap between a metal particle and a sample. In the present study, we exploited the magnetic properties of $\mathrm{Fe3O4} / \mathrm{Au}$ nanoparticle aggregates to make closer contact between the graphene film and the gold nanostructures on the Si substrate in the presence of an external magnetic field. Such an approach resulted in increasing the intensity of graphene G mode with the enhancement factor of 5. The first findings and further perspectives on the study are discussed.

Room temperature lateral p+-i-n+ light-emitting diodes (LEDs) with photonic crystals embedded in the i-region were fabricated on structures with Ge(Si) self-assembled islands and their optical properties were investigated. The use of preliminary amorphization and solid phase epitaxy of the implanted p+ and n+ contact regions made it possible to reduce the impurity activation temperature from 800 degrees C-1100 degrees C to 600 degrees C, which corresponds to the growth temperature of Ge(Si) islands. This resulted in a significant reduction of the detrimental effect of the high-temperature annealing used for diode formation on the intensity and spectral position of the luminescence signal from the islands. It was shown that significant enhancement (more than an order of magnitude) of room temperature electroluminescence of Ge(Si) islands in the spectral range of 1.3-1.55 mu m can be achieved due to their interaction with different modes of the photonic crystals. The measured radiation power of the obtained diodes in the spectral range of 1.3-1.55 mu m exceeds 50 pW at a pump current of 8 mA, which is an order of magnitude higher than the previously achieved values for micro-LEDs with Ge(Si) nanoislands. The obtained results open up new possibilities for the realization of silicon-based light emitting devices operating at telecommunication wavelengths.

The emission properties of ordered arrays of silicon disk-like resonators with embedded GeSi quantum dots are studied. It is shown that, depending on the distance between the resonators, the structures can exhibit the properties of isolated Mie resonators or photonic crystals characterized by the presence of a contribution from photonic crystal modes in the photoluminescence spectrum. The formation of photonic crystals based on the disk-like resonators makes it possible to significantly increase the luminescence response in the wavelength range of 1.2–1.6 μm, even at room temperature.

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

Light-emitting transistors (LETs) represent the next step in the development of light-emitting diodes (LEDs), offering additional control over emission. In this work, the transport properties and spatial distribution of electroluminescence (EL) in the spectral range of 1.2-1.7 mu m were studied for lateral p(+)-i-n(+) LEDs based on silicon-on-insulator structures with self-assembled Ge(Si) islands embedded in photonic crystals. It is shown that due to the low mobility of holes and their effective trapping in the islands, the maximum EL yield is observed at the i/p(+) junction of the LED. It is demonstrated that the sign and magnitude of the bias voltage applied to the substrate (to the gate) have a significant influence on the transport and emission properties of the LEDs with Ge(Si) islands, turning them into LETs. In particular, applying a negative gate voltage shifts the position of the maximum emission region from the i/p(+) to the i/n(+ )junction of the LET, which is related to the formation of a hole conductivity channel near the buried oxide layer. The embedding of a specially designed photonic crystal in the i-region of the LET makes it possible to manage the spectral properties of the near-IR emission by changing the sign of the gate voltage. The results obtained may be useful for the future development of optoelectronic devices.

The emission properties of a single Si microdisk resonator with a deterministically embedded GeSi quantum dot (QD) stack have been investigated. The results demonstrate selective excitation of different modes of the resonator depending on the position of QDs. The photoluminescence (PL) spectrum changes dramatically depending on the location of the QDs in the resonator. For the central QD position, the excitation of low Q-factor Mie modes with high field concentration in the center of resonator results in the appearance of a broad PL band. When the stack of QDs is shifted from the center to the edge of the Si resonator, the quenching of this PL band is observed and narrow PL peaks corresponding to whispering gallery modes (WGMs) appear in the PL spectrum. It is found that resonator modes can be excited not only by QDs but also by the radiation of the wetting layer. It is shown that a GeSi island on the top of the QD stack, not covered by silicon, can play the role of a nanoantenna, redirecting radiation to the upper half-space, which is especially important for WGMs that usually radiate sideways.

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 effects of GeSi quantum dot emission coupling with the collective modes in the linear chains of Si disk resonators positioned on an SiO2 layer. The emission spectra as a function of the chain period and disk radius were investigated using micro-photoluminescence (micro-PL) spectroscopy. At optimal parameters of the disk chains, two narrow PL peaks, with quality factors of around 190 and 340, were observed in the range of the quantum dot emission. A numerical analysis of the mode composition allowed us to associate the observed peaks with two collective modes with different electric field polarization relative to the chain line. The theoretical study demonstrates the change of the far-field radiation pattern with increasing length of the disk chain. The intensive out-of-plane emission was explained by the appearance of the dipole mode contribution. The obtained results can be used for the development of Si-based near-infrared light sources.

This work is devoted to the study of plasmon-enhanced Raman scattering by the fundamental vibrational modes of multilayered graphene films. The film thickness was similar to 3.5 nm, which corresponds to similar to 10 monolayers. Multilayered graphene films were placed on a plasmonic substrate consisting of arrays of gold nanodisks (50-250 nm in diameter). Surface-enhanced Raman scattering by the main vibrational modes of multilayered graphene film placed on an array of Au nanodisks of various sizes was implemented. The measurements were performed at excitation wavelengths of 532, 638, and 785 nm. A resonant SERS enhancement of the main vibrational modes of multilayered graphene by a factor of 25 was achieved for nanodisks with a diameter of 103 nm upon excitation at 638 nm. A stronger local enhancement of Raman scattering in multilayered graphene (by a factor of 50) placed on Au nanodisk array is achieved using gap-mode tip-enhanced Raman scattering (gap-mode TERS). Nanofolds in the graphene film appeared due to the corrugated surface of the plasmonic substrate were visualized with nanometer spatial resolution. It is shown that the frequency positions of G and 2D modes of nanofolds decrease with respect to the corresponding values in flat multilayered graphene manifesting mechanical stresses in the nanofolds up to 0.7%. The results obtained shed light on the effects of the interaction of multilayered graphene with metal nanostructures and are important in creating hybrid metal/graphene plasmonic substrates.

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.

Two-dimensional Si-based photonic crystals with embedded Ge nanoislands were studied. In particular, dependences of the steady-state and time-resolved photoluminescence response on the depth of the air-holes which form the photonic crystal itself were investigated. It was shown that the maximum luminescence intensity was observed not for the fully-etched photonic crystals but for the intermediately etched ones. The possible origin of such a behavior is discussed. Keywords: SiGe heterostructures, Ge islands, Photonic crystals, Photoluminescence, non-radiative recombination.

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.

More than an order of magnitude enhancement of the room-temperature photoluminescence (PL) signal from rather thick germanium layers grown on Si(001) was obtained through the utilization of 2D photonic crystals (PhCs). A set of PhCs with different periods and filling factors was fabricated and studied using micro-PL spectroscopy. Optical features of the fabricated PhCs were also theoretically modeled using rigorously coupled wave analysis, which allowed us to bring the observed peaks in the PL response into correlation with the different modes of PhC. In particular, we were able to associate the well-resolved peaks in the PL spectra with the optically active modes of the PhCs. The obtained results proved the possibility of using a homogeneously distributed active medium in PhCs without the formation of specially designed cavities in order to redistribute the internal emitted light into the required modes and efficiently extract it in the far field. The relative simplicity and higher tolerance to fabrication imperfections, as well as the large working area of these kinds of PhCs compared to PhCs with microcavities, can be advantageous for creating a PhC-based Si-compatible light source for the telecom band.

We report on the highly superlinear intensity dependence of the photosignal from quantum point contacts. In our experiments, the devices were made of GaAs quantum wells operating in the deep tunneling regime ($G_{dark} \lt 2e^{2}/h$). With low-power, continuous-wave terahertz laser radiation, the photoconductance increased exponentially with intensity and enlarged by nearly four orders of magnitude with as little as 1000 mW/cm 2 . This effect occurred only for a radiation electric field aligned with the source-drain direction. We attribute this intense effect to the local diffraction of the incident field, modifying the height of the tunnel barrier. Further, we showed that a magnetic field suppresses the photoresponse, especially under conditions of cyclotron resonance.

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.

Magneto-intersubband oscillations in a highly mobile two-subband electron system with one-dimensional periodic modulation of the potential under the conditions of overlapping Landau bands have been experimentally investigated. A significant modification of magneto-intersubband oscillations relative to the amplitude and phase is found: the amplitude decreases and the reversal of magneto-intersubband oscillations occurs in some ranges of magnetic fields. The obtained experimental data can be explained by a two-humped structure of the electron energy spectrum in Landau bands.