Monolayer molybdenum disulphide (MoS 2 ) has attracted much attention, due to its attractive properties, such as two-dimensional properties, direct bandgap, valley-selective circular dichroism, and valley Hall effect. However, some of its fundamental physical parameters, e.g. refractive index, have not been studied in detail because of measurement difficulties. In this work, we have synthesized highly crystalline monolayer MoS 2 on SiO 2 /Si substrates via chemical vapor deposition (CVD) method and devised a method to measure their optical contrast spectra. Using these contrast spectra, we extracted the complex refractive index spectrum of monolayer MoS 2 in the wavelength range of 400 nm to 750 nm. We have analyzed the pronounced difference between the obtained complex refractive index spectrum and that of bulk MoS 2 . The method presented here is effective for two-dimensional materials of small size. Furthermore, we have calculated the color contour plots of the contrast as a function of both SiO 2 thickness and incident light wavelength for monolayer MoS 2 using the obtained refractive index spectrum. These plots are useful for both fundamental study and device application.

Transition metal dichalcogenides with intrinsic spin-valley degrees of freedom hold great potentials for applications in spintronic and valleytronic devices. MoS monolayer possesses two inequivalent valleys in the Brillouin zone, with each valley coupling selectively with circularly polarized photons. The degree of valley polarization (DVP) is a parameter to characterize the purity of valley-polarized photoluminescence (PL) of MoS monolayer. Usually, the detected values of DVP in MoS monolayer show achiral property under optical excitation of opposite helicities due to reciprocal phonon-assisted intervalley scattering process. Here, it is reported that valley-polarized PL of MoS can be tailored through near-field interaction with plasmonic chiral metasurface. The resonant field of the chiral metasurface couples with valley-polarized excitons, and tailors the measured PL spectra in the far-field, resulting in observation of chiral DVP of MoS -metasurface under opposite helicities excitations. Valley-contrast PL in the chiral heterostructure is also observed when illuminated by linearly polarized light. The manipulation of valley-polarized PL in 2D materials using chiral metasurface represents a viable route toward valley-polaritonic devices.

which are environmentally friendly and enable portability and high efficiency. Up to date, great progress has been made on the UVC light-emitting diodes (LEDs) by using active regions of AlGaN multiple quantum wells (MQWs) .[8-14] However, the optical output power of current UVC LEDs drops significantly as the light emission wavelength gets shorter. Those LEDs suffer from poor hole injection efficiency in high-Al-content p-type AlGaN, low internal quantum efficiency (IQE) caused by large-lattice-mismatch heteroepitaxy, and strong quantum-confined Stark effect (QCSE), as well as the absorption by the nontransparent GaN contact layers. [15][16][17] A promising approach that dramatically improves the light output power is electron-beam (e-beam) pumping, especially for the short-wavelength UVC spectral range. [3,[18][19][20][21][22][23][24] This approach allows one to bypass the need for p-type or n-type injection layers and, thus, can largely increase the carrier injection efficiency. This provides a unique advantage over conventional LEDs at UVC range, since the p-type doping for high-Al-content AlGaN is High-output-power electron-beam (e-beam) pumped deep ultraviolet (DUV) light sources, operating at 230-270 nm, are achieved by adjusting the well thickness of binary ultrathin GaN/AlN multiple quantum wells. These structures are fabricated on high-quality thermally annealed AlN templates by metal-organic chemical vapor deposition. Owing to the reduced dislocation density, large electron-hole overlap, and efficient carrier injection by e-beam, the DUV light sources demonstrate high output powers of 24.8, 122.5, and 178.8 mW at central wavelengths of 232, 244, and 267 nm, respectively. Further growth optimization and employing an e-gun with increased beam current lead to a record output power of ≈2.2 W at emission wavelength of ≈260 nm, the key wavelength for water sterilization. This work manifests the practical levels of high-output-power DUV light sources operated by using e-beam pumping method. The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/adom.201801763.Solid-state deep ultraviolet (DUV) optoelectronic devices in the spectral range of 200-280 nm, i.e., ultraviolet-C (UVC), have attracted much attention for their wide applications in sterilization, medical treatment, security, solar-blind photodetection, and so on. [1][2][3][4][5][6][7] Currently, Al(Ga)N material system is the most promising candidate for solid-state UVC light sources

The world‐wide spreading of coronavirus disease (COVID‐19) has greatly shaken human society, thus effective and fast‐speed methods of non‐daily‐life‐disturbance sterilization have become extremely significant. In this work, by fully benefitting from high‐quality AlN template (with threading dislocation density as low as ≈6×10 8 cm −2 ) as well as outstanding deep ultraviolet (UVC‐less than 280 nm) light‐emitting diodes (LEDs) structure design and epitaxy optimization, high power UVC LEDs and ultra‐high‐power sterilization irradiation source are achieved. Moreover, for the first time, a result in which a fast and complete elimination of SARS‐CoV‐2 (the virus causes COVID‐19) within only 1 s is achieved by the nearly whole industry‐chain‐covered product. These results advance the promising potential in UVC‐LED disinfection particularly in the shadow of COVID‐19.

Quasi-2D GaN layers inserted in an AlGaN matrix are proposed as a novel active region to develop a high-output-power UV light source. Such a structure is successfully achieved by precise control in molecular beam epitaxy and shows an amazing output power of ≈160 mW at 285 nm with a pulsed electron-beam excitation. This device is promising and competitive in non-line-of-sight communications or the sterilization field.

SiQDs with an average diameter of 2.6 ± 0.5 nm are used as the light emitting material in high-efficiency inverted structure light emitting diodes.

Spintronic devices rely on the spin degree of freedom (DOF), and spin orbit coupling (SOC) is the key to manipulate spin DOF. Quasi-one-dimensional structures, possessing marked anisotropy gives more choice for the manipulation of the spin DOF since the concrete SOC form varies along with crystallographic directions. The anisotropy of the Dresselhaus SOC in cadmium selenide (CdSe) nanobelt and nanowire was studied by circular photogalvanic effect. It was demonstrated that the Dresselhaus SOC parameter is zero along the [0001] crystallographic direction, which suppresses the spin relaxation and increases the spin diffusion length, and thus is beneficial to the spin manipulation. To achieve a device structure with Rashba SOC presence and Dresselhaus SOC absence for manipulating the spin DOF, an ionic liquid gate was produced on a nanowire grown along the [0001] crystallographic direction, and the Rashba SOC was induced by gating, as expected.

Lattice polarity is a key point for hexagonal semiconductors such as GaN. Unfortunately, only Ga-polarity GaN have been achieved on graphene till now. Here, the epitaxy of high quality nitrogen-polarity GaN films on transferred graphene on non-polar sapphire substrates by molecular beam epitaxy is reported. This success is achieved through atomic nitrogen irradiation, where CN bonds are formed in graphene and provide nucleation sites for GaN and leading to N-polarity GaN epitaxy. The N-polarity characteristics are confirmed by chemical etching and transmission electron microscopy measurement. Due to the higher growth temperature of InGaN at N-polarity than that at Ga-polarity, green light emitting diodes are fabricated on the graphene-assisted substrate, where a large redshift of emission wavelength is observed. These results open a new avenue for the polarity modulation of III-nitride films based on 2D materials, and also pave the way for potential application in longer wavelength light emitting devices. nucleation but also lead to the N-lattice-polarity of the following grown GaN, as further confirmed by chemical etching and transmission electron microscopy measurement. The subsequent growth by MOVPE follows the N-lattice-polarity, which makes it easy to obtain the high In-composition InGaN and thus to fabricate the N-polarity nitrides-based green LEDs on graphene/sapphire for the first time.