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Organic–inorganic layered perovskites, or Ruddlesden–Popper perovskites, are two-dimensional quantum wells with layers of leadhalide octahedra stacked between organic ligand barriers. The combination of their dielectric confinement and ionic sublattice results in excitonic excitations with substantial binding energies that are strongly coupled to the surrounding soft, polar lattice. However, the ligand environment in layered perovskites can significantly alter their optical properties due to the complex dynamic disorder of the soft perovskite lattice. Here, we infer dynamic disorder through phonon dephasing lifetimes initiated by resonant impulsive stimulated Raman photoexcitation followed by transient absorption probing for a variety of ligand substitutions. We demonstrate that vibrational relaxation in layered perovskite formed from flexible alkyl-amines as organic barriers is fast and relatively independent of the lattice temperature. Relaxation in layered perovskites spaced by aromatic amines is slower, although still fast relative to bulk inorganic lead bromide lattices, with a rate that is temperature dependent. Using molecular dynamics simulations, we explain the fast rates of relaxation by quantifying the large anharmonic coupling of the optical modes with the ligand layers and rationalize the temperature independence due to their amorphous packing. This work provides a molecular and time-domain depiction of the relaxation of nascent optical excitations and opens opportunities to understand how they couple to the complex layered perovskite lattice, elucidating design principles for optoelectronic devices.

Two-dimensional (2D) organic-inorganic hybrid perovskites feature characteristics of inherent quantum-well structures and intriguing optoelectronic properties, and have therefore attracted enormous research attention for their optical applications in light emitting, sensing, modulation, and telecommunication devices. The low-cost and solution-processed fabrications as well as alternative organic spacer cations endue 2D hybrid perovskites with higher tunability in optical and photonic applications. In particular, they demonstrate distinguished nonlinear optical characters such as second-harmonic generation (SHG), two-photon absorption (2PA), and saturable absorption (SA) under the excitation of laser pulses. Here, we discuss the construction of the various sorts of 2D hybrid perovskites with different structural features. We have also highlighted some representative properties and applications of these 2D hybrid perovskites in both linear and nonlinear optical regimes.

Highly doped semiconductor quantum wells (QWs) exhibit strong intersubband transitions resulting from nanoscale electron confinement. Coupling photons to these collective dipoles in this anisotropic quantum structure enables intersubband polaritons with strong nonlinear optical response and hyperbolicity. Analogous to epitaxially grown multi-quantum wells, two-dimensional (2D) van der Waals (vdW) semiconductor heterostructures provide a compelling alternative platform, offering additional degrees of freedom and exceptional optoelectronic properties. Here we report intersubband polaritons in multilayer vdW WSe 2 QWs with broadband tunability. By oxidizing the top WSe 2 layer into a self-limiting native oxide, we activate charge transfer–induced efficient, high-density doping, enabling strong intersubband transitions and directly visualized polariton propagation. Lithographically defined nanostructures reveal their hyperbolic nature and sub-diffractional confinement, while electrostatic gating offers dynamic dispersion control. These results position vdW multilayers as a highly adaptable platform for tunable mid-infrared nanophotonics and integrated polaritonic circuits, detectors, and light sources. Confinement effects enable the design of intersubband polaritons (ISPs) in semiconductor quantum wells (QWs), but this type of light-matter excitations has been rarely explored in van der Waals materials. Here, the authors report the observation of hyperbolic ISPs in WO x /WSe 2 QW heterostructures with electrically tunable dispersions.

A persistent spin helix Just as a body moving in a vacuum tends to stay in motion, the axis of a spinning electron tends to remain fixed in direction. Both phenomena are conservation laws that ultimately derive from the uniformity of empty space. By contrast, an electron moving in a semiconductor sees a lattice of charged atoms flying past at nearly 1% of light speed, causing its spin direction to fluctuate wildly. Now Koralek et al . demonstrate that the application of an external electric field to a semiconductor can precisely balance the spin-destabilizing effect of the charged lattice. The collective spin of the entire gas of electrons, rather than that of each individual particle, then emerges as a new conserved quantity — a property well suited for 'spintronics' applications. The axis of a spinning electron tends to remain fixed in direction: in contrast, an electron moving in a semiconductor sees a lattice of charged atoms flying past, causing its spin direction to fluctuate. Koralek and colleagues demonstrate that an electric field applied to the semiconductor can balance this spin-destabilizing effect; the collective spin of the entire gas of electrons is conserved, a property well-suited for 'spintronics' applications. According to Noether’s theorem 1 , for every symmetry in nature there is a corresponding conservation law. For example, invariance with respect to spatial translation corresponds to conservation of momentum. In another well-known example, invariance with respect to rotation of the electron’s spin, or SU(2) symmetry, leads to conservation of spin polarization. For electrons in a solid, this symmetry is ordinarily broken by spin–orbit coupling, allowing spin angular momentum to flow to orbital angular momentum. However, it has recently been predicted that SU(2) can be achieved in a two-dimensional electron gas, despite the presence of spin–orbit coupling 2 . The corresponding conserved quantities include the amplitude and phase of a helical spin density wave termed the ‘persistent spin helix’ 2 . SU(2) is realized, in principle, when the strengths of two dominant spin–orbit interactions, the Rashba 3 (strength parameterized by α ) and linear Dresselhaus 4 ( β 1 ) interactions, are equal. This symmetry is predicted to be robust against all forms of spin-independent scattering, including electron–electron interactions, but is broken by the cubic Dresselhaus term ( β 3 ) and spin-dependent scattering. When these terms are negligible, the distance over which spin information can propagate is predicted to diverge as α approaches β 1 . Here we report experimental observation of the emergence of the persistent spin helix in GaAs quantum wells by independently tuning α and β 1 . Using transient spin-grating spectroscopy 5 , we find a spin-lifetime enhancement of two orders of magnitude near the symmetry point. Excellent quantitative agreement with theory across a wide range of sample parameters allows us to obtain an absolute measure of all relevant spin–orbit terms, identifying β 3 as the main SU(2)-violating term in our samples. The tunable suppression of spin relaxation demonstrated in this work is well suited for application to spintronics 6 , 7 .

The calculation of the limiting efficiency and structural optimization of solar cells based on the detailed balance principle is systematically investigated in this study. Through modeling and numerical simulations of various cell architectures, the theoretical efficiency limits of these structures under AM1.5G (Air Mass 1.5 Global) spectrum were quantitatively evaluated. Through a comprehensive consideration of the effects of bandgap and composition, the Al0.03Ga0.97As/Ge (1.46 eV/0.67 eV) cell configuration was determined to achieve a high theoretical efficiency of 43.0% for two-junction cells while maintaining satisfactory lattice matching. Furthermore, the study proposes that incorporating a Ga0.96In0.04As (8.3 nm)/GaAs0.77P0.23 (3.3 nm) strain-balanced multiple quantum wells (MQWs) structure enables precise bandgap engineering, modulating the effective bandgap to the optimal middle-cell value of 1.37 eV, as determined by graphical analysis for triple junctions. This approach effectively surpasses the efficiency constraints inherent in conventional bulk-material III–V semiconductor solar cells. The results demonstrate that an optimized triple-junction solar cell with MQWs can theoretically achieve a conversion efficiency of 51.5%. This study provides a reliable theoretical foundation and a feasible technical pathway for the design of high-efficiency solar cells, especially for the emerging MQW-integrated III–V semiconductor tandem cells.

We report a monolithic GaN-based light-emitting diode (LED) platform capable of color-tunable white-light emission via LED size scaling. By varying the LED size from 800 µm to 50 µm, the injection current density was effectively controlled under constant driving current, enabling precise modulation of carrier distribution within a dual-composition multi-quantum well (MQW) structure. The active layer consists of five lower In0.15Ga0.85N/GaN QWs for blue emission and strain induction, and an upper In0.3Ga0.7N/GaN single QW engineered for red-orange emission. The strain imposed by lower QWs promotes indium segregation in the last QW through spinodal decomposition, resulting in a broadened emission spanning from ~500 nm to 580 nm. High-resolution TEM and EDX analyses directly confirmed the indium segregation and phase-separated structure of the last QW. Spectral analysis revealed that larger devices exhibited dominant emission at 580 nm with a correlated color temperature (CCT) of 2536 K and a CIE coordinate of (0.501, 0.490). As LED size decreased, increased hole injection allowed recombination to occur in deeper QWs, resulting in a blueshift to 450 nm and a CCT of 9425 K with CIE (0.224, 0.218) in the 50 × 50 µm2 LED. This approach enables phosphor-free white-light generation with tunable color temperatures and chromaticities using a single wafer, offering a promising strategy for compact, adaptive solid-state lighting applications.

The relationship between electron state density and energy in deep ultraviolet laser diodes (LDs) with quantum well (QW) structures exhibits a step-like shape, which enhances differential gain and light confinement of the LD. However, the active layer in QW structures typically has limited ability to collect equilibrium carriers, leading to an increased threshold current. Quantum dot (QD) structures address this limitation by imposing quantum confinement on charge carriers in three dimensions, thereby reducing optical losses and improving carrier confinement. Despite these advantages, the presence of numerous QDs often introduces synthetic imperfections (e.g. size and shape variations) and surface/interface defects, which cause light to split into multiple wavelengths. This study investigated the embedding of QDs into AlGaN QWs and evaluated the impact of QD size on device performance. This configuration addresses the weak carrier collection in QW structures and leverages QDs to quantum-constrain carrier movement, while avoiding the problem of high threshold current densities due to the large number of QDs that are not uniform in size and indicative of defects. For a QW thickness of 4 nm, an optimal QD thickness of 1 nm was determined, enabling effective utilization of both QDs and QWs. This configuration led to a substantial increase in LD output power and a decrease in threshold current. Specifically, the output power of the LD with a 1 nm thick QD increased by 13.6 times, while the threshold current decreased by 63.6% compared to the QW structure alone. Besides, the findings also revealed that QD thickness significantly affects the photoelectric properties of the LD. Excessively thick QDs can form depressions in the middle of QWs, which lowers the restriction on charge carriers. Conversely, QDs that are too thin cannot effectively take advantage of the three-dimensional carrier constraints of QDs, thereby reducing the light confinement capability.

This paper explores the propagation loss in waveguides on directly bonded InP/Si substrates, using numerical simulations to understand the effect of voids within the waveguide structure. Using COMSOL Multiphysics, we developed a model to simulate light propagation, focusing on how void characteristics such as diameter and angle influence the propagation loss. Our findings reveal a correlation between void dimensions and the increased threshold current density in separate confinement heterostructure multiple quantum well laser diodes, thereby providing insights into optimizing waveguide design for enhanced laser performance on InP/Si substrates. This research underscores the critical role of substrate bonding quality in minimizing internal losses and improving device efficiency.

Growth and characterization of advanced group IV semiconductor materials with CMOS‐compatible applications are demonstrated, both in photonics. The investigated GeSn/SiGeSn heterostructures combine direct bandgap GeSn active layers with indirect gap ternary SiGeSn claddings, a design proven its worth already decades ago in the III–V material system. Different types of double heterostructures and multi‐quantum wells (MQWs) are epitaxially grown with varying well thicknesses and barriers. The retaining high material quality of those complex structures is probed by advanced characterization methods, such as atom probe tomography and dark‐field electron holography to extract composition parameters and strain, used further for band structure calculations. Special emphasis is put on the impact of carrier confinement and quantization effects, evaluated by photoluminescence and validated by theoretical calculations. As shown, particularly MQW heterostructures promise the highest potential for efficient next generation complementary metal‐oxide‐semiconductor (CMOS)‐compatible group IV lasers. The formation of Si–Ge–Sn‐based direct bandgap group IV heterostructures proves to be a viable path toward highly efficient integrated light emitters. While GeSn/SiGeSn double heterostructures already show optically pumped lasing, additional benefits are expected in multi‐quantum well structures. Efficient separation of carriers from defects gives rise to considerably increased nonradiative carrier lifetimes in the latter.

Comparing transport properties through electron mobility in current semiconductor materials is one of the ways to find high-performance and cost-effective electronic components. In this study, we investigate the mobility of a two-dimensional electron gas (2DEG) confined within finitely deep versus infinitely deep triangular quantum wells in AlGaN/GaN heterostructures (SHs). Using the variational subband-wave-function model, we analyze a comprehensive set of scattering mechanisms, including edge dislocation (DS), charged dislocation (DC), remote impurity (RI), interface roughness (IR), roughness-induced piezoelectric effects (PE), misfit deformation potential (DP), acoustic phonons, piezoelectric fields, and polar optical longitudinal optical (LO) phonons. Acoustic phonon scattering is treated as quasi-elastic, while inelastic scattering is addressed using an iterative method, with LO phonon scattering becoming dominant at higher temperatures. Our findings show that, in finitely deep quantum wells with lower potential barriers, electron mobility is primarily influenced by DS, DC, and IR scattering mechanisms. In contrast, infinitely deep quantum wells exhibit higher mobility, where RI, DP, PE, acoustic phonons, and LO phonons play a more significant role. Based on this quantum well mobility comparison, manufacturers know which scattering mechanism is dominant according to temperature or density, to adjust and increase the efficiency of the scattering mechanisms. Overall, our results highlight that infinitely deep triangular quantum wells offer superior electron mobility, making them promising for future high-performance electronic materials and devices.