Two-dimensional heterostructures have been crucial in advancing optoelectronic devices utilizing van der Waals materials. Semiconducting transition-metal dichalcogenide monolayers, known for their unique optical properties, offer extensive possibilities for light-emitting devices. Recently, a memory-driven optical device, termed a Mem-emitter, was proposed by using these monolayers atop dielectric substrates. The successful realization of such devices heavily depends on the selection of the optimal substrate. Here, we report a pronounced memory effect in a MoSe2/clinochlore device, evidenced by an electric hysteresis in the intensity and energy of MoSe2 monolayer emissions. This demonstrates both population- and transition-rate-driven Mem-emitter abilities. Our theoretical approach correlates these memory effects with internal state variables of the substrate, emphasizing that a clinochlore-layered structure is crucial for a robust and rich memory response. This work introduces a novel two-dimensional device with promising applications in memory functionalities, highlighting the importance of alternate insulators in the fabrication of van der Waals heterostructures.

Concurrent natural time scales related to relaxation, recombination, trapping, and drifting processes rule the semiconductor heterostructures' response to external drives when charge carrier fluxes are induced. This paper highlights the role of stoichiometry not only for the quantitative tuning of the electron-hole dynamics but also for significant qualitative contrasts of time-resolved optical responses during the operation of resonant tunneling devices. Therefore, similar device architectures and different compositions have been compared to elucidate the correlation among structural parameters, radiative recombination processes, and electron-hole pair and minority carrier relaxation mechanisms. When these ingredients intermix with the electronic structure in Sb-based tunneling devices, it is proven possible to assess various time scales according to the intensity of the current flux, contrary to what has been observed in As-based tunneling devices with similar design and transport characteristics. These time scales are strongly affected not only by the filling process in the $\Gamma$ and L states in Sb-based double-barrier quantum wells but also by the small separation between these states, compared to similar heterostructures based on As.

AlInAs/AlGaAs quantum dots (QDs) have emerged as excellent emitters across the visible spectral range, showcasing highly tunable electronic properties through variations in composition and size. This versatility allows for diverse band alignments within the same system. In this study, we present compelling evidence for the coexistence of type-I indirect and direct emissions from QDs, supported by comprehensive analyses of their photoluminescence responses to excitation power, temperature, and time, along with band structure calculations. The high-density QD system exhibits signs of lateral coupling, facilitated by carrier transfer between dots, modulated by energy barriers and recombination times. Additionally, we can unequivocally prove that the QDs act as carrier reservoirs that progressively feed optically active states in the bulk GaAs at low temperatures & horbar;an attractive prospect for hot-carrier photovoltaics. Above certain temperatures, the bulk system reverts to the anticipated predominantly radiative recombination dynamics. Our theoretical framework, accounting for the coexistence of QD specimens with varying recombination times, successfully elucidates the optical response at different temperatures, emphasizing the pivotal role of QD excitation in enhancing the effective lifetime of carriers in the bulk.

Topological two-dimensional transition metal dichalcogenides (TMDs) have a wide range of promising applications and are the subject of intense basic scientific research. Due to the existence of a direct optical bandgap, nano-optics and nano-optoelectronics employing monolayer TMDs are at the center of the development of next-generation devices. Magneto-resonant Raman scattering (MRRS) is a non-destructive fundamental technique that enables the study of magneto-electronic levels for TMD semiconductor device applications and hitherto unexplored optical transitions. Raman intensity in a Faraday backscattering configuration as a function of the magnetic field B, laser energy, and the circular polarization of light reveals a set of incoming and outgoing resonances with particular spin orientations and magneto-optical interband transitions at the K- and K′-valleys of the Brillouin zone. This fact unequivocally allows for a straightforward determination of the important band parameters of TMD materials. A generalization of the MRRS theory is performed for the description of the magneto-polaron (MP) effects in the first-order light scattering process. It shows how strongly the simultaneous presence of the conduction and valence bands modifies the MP energy spectrum. The resonant MP Raman intensity reveals three resonant splitting processes of double avoided-crossing levels reflecting the electron-hole pair energy spectrum. The scattering profile allows for quantifying the relative contribution of the conduction and valence bands in the formation of MPs. Many avoided-crossing points due to the electron–phonon interaction in the MP spectrum, a superposition of the electron and hole states in the excitation branches, and their impact on Raman scattering are exceptional features of monolayer TMDs. Based on this, the reported theoretical studies open a pathway toward MRRS and resonant MP Raman scattering characterization of two-dimensional materials.

The impact of the growth orientation on spin dynamics in GaAs/AlGaAs quantum wells (QWs) is explored through magnetophotoluminescence measurements. Samples grown on both (100) and (311)A GaAs surfaces exhibit intensity oscillations at high magnetic fields, characteristic of magnetoabsorption arising from interband transitions between Landau levels when excited near resonance. Notably, the (311)A surface reveals optical responses rarely observed on the conventional (100) surface, including an inversion in circular polarization degree influenced by both excitation power and temperature. To elucidate these findings, we develop an eight-level model encompassing electron and hole excited states. Our analysis demonstrates that thermalization is the primary and sufficient factor responsible for reproducing spin inversion with external parameters.

Phonon spectra of transition metal dichalcogenides are studied using first principles calculations and Born–Huang model phenomenological description.

Magneto-optical measurements are fundamental research tools that allow for studying the hitherto unexplored optical transitions and the related applications of topological two-dimensional (2D) transition metal dichalcogenides (TMDs). A theoretical model is developed for the first-order magneto-resonant Raman scattering in a monolayer of TMD. A significant number of avoided crossing points involving optical phonons in the magneto-polaron (MP) spectrum, a superposition of the electron and hole states in the excitation branches, and their manifestations in optical transitions at various light scattering configurations are unique features for these 2D structures. The Raman intensity reveals three resonant splittings of double avoided-crossing levels. The three excitation branches are present in the MP spectrum provoked by the coupling of the Landau levels in the conduction and valence bands via an out-of-plane $$A_1$$ A 1 -optical phonon mode. The energy gaps at the anticrossing points in the MP scattering spectrum are revealed as a function of the electron and hole optical deformation potential constants. The resonant MP Raman scattering efficiency profile allows for quantifying the relative contribution of the conduction and valence bands in the formation of MPs. The results obtained are a guideline for controlling MP effects on the magneto-optical properties of TMD semiconductors, which open pathways to novel optoelectronic devices based on 2D TMDs.

The influence of the valence band structure on the optical properties of quantum wells with a parabolic potential, consisting of AlxGa1-xAs and In1-xGaxAsyP1-y alloys, is studied and compared. The distribution of photogenerated carriers over the parabolic potential is found to be responsible for specific selection rules: the recombination due to only odd-indexed confined levels is observed. The reason for this is the accumulation of photogenerated holes at the center of the parabolic potential, which results in interband electron-hole recombination occurring at the center of the parabolic quantum wells. Furthermore, a specific valence band structure is found to be responsible for the magnetic-field-induced change in the photoluminescence circular polarization. In particular, at a certain magnetic field, the hybridization of the states of a heavy hole and a light hole results in the intersection of Landau levels with different spins, which leads to the observed change in the circular polarization of photoluminescence. The processes of long-term spin relaxation of heavy holes in both studied parabolic quantum wells are demonstrated, and the corresponding times are obtained.

Monolayer transition-metal dichalcogenides (TMDs) are emergent semiconductor materials with a wide range of potential applications. Rydberg excitons are similar to the Rydberg atomic states having a large principal quantum number n. The huge binding energies found in TMD semiconductors, up to 900 meV, facilitate studies of the Rydberg excitons, opening a new perspective of research by employing their long lifetimes, strong dipolar interactions, and the potential for coherent effects and quantum chaos. In the framework of a microscopic theory, we provide a complete description of the first-order resonant Raman scattering (RRS) valid for two-dimensional (2D) TMD semiconductors. Assuming as electronic intermediate states the high-n exciton states, we present explicit expressions for the RRS intensity, which are valid for incident laser energies close to the excitonic resonances. The intravalley Pekar-Frohlich polar longitudinal optical mode and A(1)-homopolar mode deformation potential coupling mechanisms are considered. We report a large enhancement of the Raman efficiency due to the simultaneous incoming and outgoing resonances with bound exciton states, occurring for an appropriate choice of the excitation photon energy. We show that the 2D semiconductors guarantee the necessary conditions for the doubly RRS (DRRS) when intravalley transitions occur between two different Rydberg states separated by an optical phonon energy. The observation of the intravalley DRRS process can open new perspectives for deeper studies of the role of Rydberg excitons in solid-state physics.

In this work, carrier transport in a gold-seeded zinc diphosphide nanowire fabricated by vapor–liquid–solid and photolithography techniques is investigated in detail.

The control of native defects in the ZnO material is strongly important for a wide range of technological applications. In this paper, native defects are tuned via the post-thermal treatment of ZnO films in a high vacuum atmosphere. The microstructure of the as-grown ZnO film shows columnar growth and strongly polar-oriented grains along the c-plane (002). Also, the obtained results indicate that the as-grown film contains a high amount of intrinsic defects and strong lattice distortions. After the thermal annealing, the ZnO films display significant structural changes, which are reflected in their electrical, vibrational, and optical properties. Our findings suggest that these changes were attributed to the selective cleanup effect of the native defects and the partial deoxidation process mainly on the exposed particle surface (at high temperatures) tuned up by the thermal annealing temperature. According to DFT calculations, oxygen vacancies (V O ) show lower energy, followed by zinc vacancies (V Zn ) and oxygen interstitials (O i ) indicating that V O defect is the most stable in ZnO. That sequence of stability could suggest the sequence of the annihilation of those defects, which is in line with our experimental findings and also in agreement with literature results.

This paper discusses the combined effects of optical excitation power, interface roughness, lattice temperature, and applied magnetic fields on the spin coherence of excitonic states in GaAs/AlGaAs multiple quantum wells. For low optical powers, at lattice temperatures between 4 and 50 K, the scattering with acoustic phonons and short-range interactions appear as the main decoherence mechanisms. Statistical fluctuations of the band gap, however, become also relevant in this regime and we were able to deconvolute them from the decoherence contributions. The circularly polarized magneto-photoluminescence unveils a nonmonotonic tuning of the coherence for one of the spin components at low magnetic fields. This effect has been ascribed to the competition between short-range interactions and spin-flip scattering, modulated by the momentum relaxation time.

This work elucidates the morphology-photoluminescence (PL) emission relationships, based on experimental and calculated results, on beta-Ag2MoO4 samples synthesized by microwave-assisted hydrothermal method. It was shown that the solvent (water and ammonia) and temperature (120, 130, 140, and 150 degrees C) play a crucial role in the morphology and PL emissions. A crystal structure model, composed by the local coordination of both Ag and Mo atoms at bulk and exposed surfaces, was built, and the possible mechanism along the synthesis progress was proposed and analyzed. This study provides an idea for the preparation and development of beta-Ag2MoO4 based materials with desirable properties.

This paper discusses the combined effects of optical excitation power, interface roughness, lattice temperature, and applied magnetic fields on the spin-coherence of excitonic states in GaAs/AlGaAs multiple quantum wells. For low optical powers, at lattice temperatures between 4 K and 50 K, the scattering with acoustic phonons and short-range interactions appear as the main decoherence mechanisms. Statistical fluctuations of the band-gap however become also relevant in this regime and we were able to deconvolute them from the decoherence contributions. The circularly polarized magneto-photoluminescence unveils a non-monotonic tuning of the coherence for one of the spin components at low magnetic fields. This effect has been ascribed to the competition between short-range interactions and spin-flip scattering, modulated by the momentum relaxation time.

This paper discusses the combined effects of optical excitation power, interface roughness, lattice temperature, and applied magnetic fields on the spin-coherence of excitonic states in GaAs/AlGaAs multiple quantum wells. For low optical powers, at lattice temperatures between 4 K and 50 K, the scattering with acoustic phonons and short-range interactions appear as the main decoherence mechanisms. Statistical fluctuations of the band-gap however become also relevant in this regime and we were able to deconvolute them from the decoherence contributions. The circularly polarized magneto-photoluminescence unveils a non-monotonic tuning of the coherence for one of the spin components at low magnetic fields. This effect has been ascribed to the competition between shortrange interactions and spin-flip scattering, modulated by the momentum relaxation time.

We investigate the energy relaxation segmentation in a resonant tunneling heterostructure by assessing the optical and transport dynamics of nonequilibrium charge carriers. The electrical and optical properties are analyzed using electronic transport measurements combined with electro- and photoluminescence spectroscopies in continuous-wave mode. Our results suggest that hot electron and hole populations form independent nonequilibrium systems that do not thermalize among them and with the lattice. Consequently, the carrier effective temperature changes independently at different regions of the heterostructure, with a population distribution for holes colder than for electrons.

We study the magneto-transport and magnetoelectroluminescence properties of purely n-doped GaAs/Al0.6Ga0.4 As resonant-tunneling diodes with an In0.15Ga0.85 As quantum well and an emitter prewell. Before the resonant-current condition, magneto-transport measurements reveal charge-carrier densities comparable for diodes with and without the emitter prewell. Landau-level splitting is observed in the electroluminescence emission from the emitter prewell, enabling the determination of the charge-carrier buildup. Our findings show that magnetoelectroluminescence spectroscopy techniques provide useful insights into the charge-carrier dynamics in resonant-tunneling diodes and comprise a versatile tool to complement magneto-transport techniques. This approach might pave the way for the development of potentially more efficient optoelectronic resonant-tunneling devices by, e.g., monitoring voltage-dependent charge accumulation for the improvement of built-in fields and hence the maximization of the photodetector efficiency and/or the minimization of optical losses.

In this paper, we conducted a combined experimental and theoretical investigation of bulk and (001) surface properties of a Ba0.5Sr0.5TiO3 (BST) material synthesized by the polymeric precursor method. Characterization techniques, such as X-ray diffraction (XRD), Raman spectroscopy, ultraviolet-visible diffuse reflectance spectroscopy, field-emission scanning electron microscopy (FE-SEM) and photoluminescence (PL), were employed to disclose the structural, electronic, and optical properties of BST. Structural analysis confirmed the BST tetragonal symmetry, showing the relevant fingerprints of structural distortions, while the crystallographic morphologies were observed in the FE-SEM images. The theoretical results evidenced the structural disorder along the tetragonal BST phase, corroborating the central role of the bonding environment in the electronic and PL properties of the material. Moreover, the (001) surface results indicated that Esurf values depend on the chemical environment of exposed surfaces following the bonding character along with A-O and Ti-O paths, which also affects the electronic structure of surface-oriented BST.

Lanthanum-doped CeO2 is a promising semiconductor for gas sensing. A combined study applying impedance spectroscopy and first-principles calculations was performed for pure and lanthanum-doped samples. The results showed a strong influence of the localized Ce 4f states on the electrical conduction processes and an electrical resistance increase as a function of the exposure to vacuum and air atmospheres. After its modification with a rare-earth element along with exposure to reducing and oxidizing atmospheres, the observed behavior suggested the presence of multitraps, which depended on the described equilibrium between the oxygen vacancies (V-o(x) <-> V-O <-> V-O) in a disordered deep-bulk trap location. According to the DFT results, the multitraps were formed with the creation of an oxygen vacancy far from the doping atom. They were considered to be responsible for the phenomena modifying the Debye-like response. The transfer of electrons from Ce(III) to the adsorbed oxygen species, decreasing the number of electrons in the 4f state, reduced the electrical conductivity by the hopping frequency dependence of the total resistance and capacitances. This was probably due to the interactions between defective oxygen and metallic species.

The search for new and low-power switching devices involving the integration of semiconductor thin films is of interest, and has led to renewed research because such devices may exhibit innovative properties. Here, we investigate the two-dimensional electron gas (2DEG) at the LaAlO3/SrTiO3 interface with metallic and insulator behavior. Insight is offered by quantifying the interface charge distribution associated with structural and electronic order-disorder effects. Variations in the electron conductivity were observed to be associated with different specific clustering arrangements of both Ti and Al cations of the co-exposed surfaces at the interface, i.e., structural and electronic connectivity among the undercoordinated [TiO5] and [AlO5] clusters. These results indicate facet control as a strategy for enhancing the electric and magnetic properties of a device via the quantum confinement of electrons.