Abstract As defects frequently govern the properties of crystalline solids, precise microscopic knowledge defect atomic structure is fundamental importance. We report a new class point in single-layer transition metal dichalcogenides that can be created through 60° rotations metal–chalcogen bonds trigonal prismatic lattice, with simplest among them being three-fold symmetric trefoil-like defect. The defects, which are inherently related to crystal symmetry dichalcogenides, expand sequential...

Raman scattering and photoluminescence (PL) emission are used to investigate a single layer of tungsten disulfide (WS${}_{2}$) obtained by exfoliating $n$-type bulk crystals. Direct gap with both neutral charged exciton recombination is observed in the low temperature PL spectra. The ratio between trion can be tuned simply varying excitation power. Moreover, intensity independently using additional subband laser excitation.

We report on detailed temperature dependent (T = 7-295 K) optical spectroscopy studies of WSe2, WS2, MoSe2 and MoS2 monolayers exfoliated onto the same SiO2/Si substrate. In high energy region absorption type (reflectivity contrast-RC) emission (photo-luminescence-PL) spectra all resonances related to neutral charged excitons (X T) are detected in entire measured range. The amplitudes trions strongly depend two dimensional carrier gas (2DCG) concentration. low PL WSe2 WS2 we detect a group...

Abstract Photon upconversion is an anti-Stokes process in which absorption of a photon leads to reemission at energy higher than the excitation energy. The photoemission has been already demonstrated rare earth atoms glasses, semiconductor quantum wells, nanobelts, carbon nanotubes and atomically thin semiconductors. Here, we demonstrate room temperature photoluminescence monolayer WS 2 , with gain up 150 meV. We attribute this transitions involving trions many phonons free exciton...

We have examined the influence of flake-substrate effects that affect one and few layers MoS2 in terms their electrical optical properties. In measurements, we used SiO2/Si substrates with etched cavities aluminum electrodes. Suspended areas are easily identifiable both on images depicting topography surface potential maps measured Kelvin probe force microscopy. Compared to supported material, decrease is observable at membrane. The value flakes located electrodes lowest. PL measurements...

Achieving significant doping in GaAs/AlAs core/shell nanowires (NWs) is of considerable technological importance but remains a challenge due to the amphoteric behavior dopant atoms. Here we show that placing narrow GaAs quantum well AlAs shell effectively getters residual carbon acceptors leading an \emph{unintentional} p-type doping. Magneto-optical studies such core multi-shell NW reveal confined emission. Theoretical calculations electronic structure confirm confinement carriers at...

We report on room temperature, polarization-resolved Raman scattering measurements layered crystals of the series MoSxSe(2–x) (0 ≤ x 2) grown by chemical vapor transport technique. The results reveal two distinct sets features related to E2g1 and A1g modes pure members series. As composition changes, in-plane mode shows two-mode behavior, whereas out-of-plane presents more complex evolution. MoSe2-like branch reveals splitting associated with altering arrangement S Se atoms around Mo...

Abstract Unlike monolayers of transition metal dichalcogenides such as MoS 2, which possess high in-plane symmetry, layered ReS 2 exhibits reduced crystal symmetry with a distorted 1 T structure. This unique leads to anisotropic optical properties, very promising for light polarization devices. Here, we report on low temperature polarization-resolved emission and absorption measurements excitons in from bulk monolayer. In photoluminescence reflectivity contrast spectra distinguish two...

Semiconducting monolayers of transition-metal dichalcogenides are outstanding platforms to study both electronic and phononic interactions as well intra- intervalley excitons trions. These excitonic complexes optically either active (bright) or inactive (dark) due selection rules from spin momentum conservation. Exploring ways brightening dark trions has strongly been pursued in semiconductor physics. Here, we report on a mechanism which exciton upconverts light into bright intravalley...

Atomically thin semiconducting transition-metal dichalcogenides enable new insight into physics of many-body effects mediated by Coulomb and electron-phonon interactions. We report photoluminescence (PL) reflectivity contrast (RC) measurements excitons ($X$) trions ($T$) Raman spectra phonons in monolayers (MLs) $\mathrm{Mo}{({\mathrm{S}}_{y}{\mathrm{Se}}_{1\ensuremath{-}y})}_{2}$ alloys with sulfur mole content up to $y=0.5$. find the phonon energy crossing trion binding content. Binary...

High-quality van der Waals heterostructures assembled from hBN-encapsulated monolayer transition metal dichalcogenides enable observations of subtle optical and spin-valley properties whose identification was beyond the reach structures exfoliated directly on standard SiO2/Si substrates. Here, we describe different based uncapped single-layer MoS2 stacked onto hBN layers thicknesses monolayers. Depending doping level, they reveal fine structure excitonic complexes, i.e. neutral charged...

In contrast to the intensively investigated transition metal dichalcogenides like ${\mathrm{MoS}}_{2}$, ${\mathrm{ReS}}_{2}$ crystals possess a reduced in-plane symmetry, leading anisotropic optical properties. Here, we report on impact of strain Raman response monolayer. Since mechanical can be used shift Raman-active phonon frequencies, apply uniaxial tensile up 0.74% along Re-chain direction ($x$ axis) atomically thin crystal and measure with scattered light polarized parallel...

The temperature dependence of the spectral features in vicinity direct band edge mixed-crystals Mo(SxSe1-x)2 solid solutions is measured range 25–295 K by using piezoreflectance (PzR). near band-edge excitonic transition energies were determined accurately from a detailed line-shape fit PzR spectra. found to vary smoothly with increase S content x, indicating that natures edges are similar. dependences analyzed Bose-Einstein expressions 25 295 K. parameters described variation and broadening...

Low-temperature photoluminescence from high-quality GaAs quantum wells, asymmetrically doped with carbon, are investigated under high magnetic fields (up to 20 T) directed along the [001] growth axis. At higher fields, in ${\ensuremath{\sigma}}^{\ensuremath{-}}$ polarized emission, we observe two well-resolved lines which attributed recombination of neutral ($X$) and charged ($X$${}^{+}$) excitons. In contrast, only exciton line is observed for ${\ensuremath{\sigma}}^{+}$ polarization. From...

Germanium monosulfide with an anisotropic puckered crystalline structure has recently attracted much attention due to its unique optical and electronic properties; however, exciton–phonon interactions were only superficially elucidated. We study the resonant Raman scattering photoluminescence of optically active Γ-exciton in layered GeS flakes evaluate exciton phonon responses on variations excitation energy, laser-light emission polarizations, temperature, laser power. A double-resonance...

Monolayers of transition metal dichalcogenides (TMDs) with their unique physical properties are very promising for future applications in novel electronic devices. In TMDs monolayers, strong and opposite spin splittings the energy gaps at K points allow exciting carriers various combinations valley indices using circularly polarized light, which can further be used spintronics valleytronics. The van der Waals heterostructures composed monolayers hexagonal boron nitride (hBN) layers...

We report on extensive polarization-resolved photoluminescence (PL) studies of a variety excitonic complexes formed in high-quality symmetric GaAs quantum wells containing high-mobility two-dimensional (2D) hole gas broad range magnetic fields from 0 to 23 T and under two-beam illumination, allowing for dynamical control the concentration beyond point conversion $p$- $n$-type structures. have demonstrated charge between positive negative bound acceptors well, differing free trions due...

Monolayers of transition-metal dichalcogenides with direct band gap located at the binary [Formula: see text] points Brillouin zone are promising materials for applications in opto- and spin-electronics due to strongly enhanced Coulomb interactions specific spin-valley properties. They furthermore represent a unique platform study electron-electron electron-phonon diverse exciton complexes. Here, we demonstrate processes which neutral biexciton two negative trions, namely spin-triplet...

Photoluminescence from bulk HfS2 grown by the chemical vapor transport method is reported. A series of emission lines apparent at low temperature in energy range 1.4–1.5 eV. Two groups observed excitonic transitions followed their replicas involving acoustic and optical phonons are distinguished using classical intensity correlation analysis. The attributed to recombination excitons bound iodine (I2) molecules intercalated between layers HfS2. I2 introduced crystal during growth as halogen...

Transition metal dichalcogenide monolayers represent unique platforms for studying both electronic and phononic interactions as well intra- intervalley exciton complexes. Here, we investigate the upconversion of photoluminescence in MoSe2 monolayers. Within nominal transparency window emission is enhanced resonantly addressing spin-singlet negative trion neutral biexciton at a few tens meV below transition. We identify that A'1 optical phonon K valley provides energy gain process resonance,...

Avoided crossing of the emission lines a nearly free positive trion and cyclotron replica an exciton bound to interface acceptor has been observed in magnetophotoluminescence spectra $p$-doped GaAs quantum wells. Identification localized state depended on precise mapping anticrossing pattern. The underlying coupling is caused by transfer combined with resonant excitation additional hole. spectrum resulting magnetically tunable coherent probes weak localization well.

This work presents an investigation of the fully strained GaAsN/GaAs heterostructures obtained by atmospheric pressure metalorganic vapor phase epitaxy, focusing on analysis strain generated in GaAsN epilayers and its correlation with formation split interstitial complexes (N-As)As. We analyzed nitrogen contents thicknesses varying from 0.93 to 1.81% 65 130 nm, respectively. The composition thickness were determined high resolution X-ray diffraction, was Raman spectroscopy, while N-bonding...

We perform a polarization-resolved magnetoluminescence study of excitons in ReS$_2$. observe that two linearly polarized Rydberg series are accompanied by other dark excitons, brightened an in-plane magnetic field. All extrapolate to the same single-electron bandgap, indicating observed originate either from valley or valleys related inversion symmetry, and split exchange interaction. To interpret our observations brightening, we have assume dominant spin-orbit coupling be Ising-like, which...