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Recently, the two-dimensional heterostructure is a research hot spot of semiconductor materials, and it has wide application prospects in electronic devices and photocatalysis. In this work, we constructed novel graphene-GaN-graphene (G-GaN-G) sandwich heterostructure, and the electronic and optical properties have been theoretically investigated based on the first principles calculations. The computation results indicate that the heterostructure is most stable when interlayer distance d0 is 3.189 A, and electronic and optical properties of intrinsic GaN and graphene are well preserved. In addition, the effect of vertical and biaxial strain on the G-GaN-G heterostructure is also investigated, we find that strain can effectively regulate the electronic and optical properties. Therefore, the electronic and optical properties of G-GaN-G can be tuned by applying different levels of strain to meet the needs of devices. This study results reveal that the G-GaN-G sandwich heterostructure can be hopefully applied to ultraviolet photodetectors and optoelectronic devices.

Based on the calculation using first-principles, we discussed adjustment for electronic properties of the GaN/graphene/WS2 trilayer vdW heterostructure by doping and biaxial strain. Mg or Se doping can regulate the band gap of the GaN/graphene/WS2 trilayer vdW heterostructure and achieve p-type or n-type dopant in graphene and the trilayer heterostructure system. Band gap decreases with the increase in positive strain, and a p-type Schottky barrier is always maintained. As the negative strain increases, the band gap reaches its maximum at e = − 3% and then gradually decreases. And after |e| ≥ | − 5|%, it changes to an indirect band gap. When |e| ≥ | − 7|%, the Schottky contact type changes from p-type to n-type. Electrons are transferred from GaN layer to graphene and WS2 layer, and transfer increases with the increase in strain from negative to positive. More electrons are transferred to WS2 with positive strain, and more electrons are transferred to graphene with negative strain. The results will provide valuable information for the design of trilayer Schottky devices.

One of the major challenges that the human beings are facing is the shortage of the fossil fuels. Hydrogen is considered as the most attractive renewable energy because of its abundant high energy density. Semiconductor photocatalytic technology for water decomposition is a promising method for converting sunlight into hydrogen energy, which has attracted considerable attention. Compared with bulk materials, two-dimensional (2D) materials exhibit remarkable photocatalytic properties. In this work, the pristine high-quality hexagonal molybdenum disulfide (MoS2) nanosheets and Ag-doped MoS2 nanosheets were synthesized by hydrothermal method, and the thickness of nanosheets was ranged from 0.9 to 1.1 nm. In addition, the absorption spectra of Ag-doped MoS2 nanosheets increased with the increase of Ag content. What's more, the photocatalytic properties of Ag-doped MoS2 nanosheets were tested, and the results show that Ag-doped MoS2 nanosheets have good stability, high hydrogen production efficiency and strong photocatalytic activity. It is worth mentioning that the photocatalytic hydrogen production rate of Ag-doped MoS2 nanosheets can reach 2695 μmol h−1 g−1. Meanwhile, density functional theory was used to calculate the optical properties, electronic structure of pristine and Ag-doped monolayer MoS2. These calculated results indicate that the absorption intensity of Ag-doped MoS2 in the ultraviolet–visible and visible light region increases significantly, and the conduction band of Ag-doped monolayer MoS2 is downshift compared with pristine MoS2. Therefore, Ag-doped MoS2 can optimize the band structure and promote the absorption of visible light, thereby improving the photocatalytic activity.

The band structure, electronic, magnetic, and optical properties of g-SiC monolayers doped with alkaline earth metals (Be, Mg, Ca, Sr, and Ba) are calculated by means of first principles based on density functional theory. Although the intrinsic g-SiC monolayer is nonmagnetic, it shows magnetic properties after doping with alkaline earth metals. The magnetic moments are, in the order of the above-named dopants, 1.583 μ B, 1817 μ B, 2.000 μ B, 2.000 μ B, and 2.000 μ B. Charge transfer and the net spin charge occur mainly between the dopant atom and surrounding C atoms. The results show that the conductivity of g-SiC can be greatly improved by doping with alkaline earth metals, a technique that can be applied to the field of semiconductor spintronics. High absorption peaks in the ultraviolet indicate that the material has potential applications in UV optoelectronic devices.

We investigated an optical amplifier and router by the aperture nonlinear phase and the phase angle of parametric amplified four-wave mixing in a thermal rubidium vapor. The three-stage optical amplifier has been realized and the total amplified gain is observed up to 10. The router action results from the multi-peaks (multi-pair two-modes) while the cross talk of router can be realized by the opposite dressing shift of composite Autler-Townes splitting.

We report Pt NP coated GaN NWs through CVD method and the fabrication of their field emitters. Pt NPs are attached on the top and surfaces of GaN NWs. With the Pt NP coating, it is found that the turn on field is reduced from 3.3 V μm−1 to 2.7 V μm−1 and the work function is decreased from 4.1 eV to 3.22 eV. In addition, DFT calculation results indicate that higher local electron states, which appear around the Fermi level, are mainly formed from N-2p, Pt-6s, and Pt-5d orbital hybridization, and will provide more electrons to the conduction band at a given operating voltage. Consequently, the field emission performance of GaN NWs can be effectively boosted by adsorbed Pt. Moreover, Pt NP coated GaN NWs are promising for electron emission devices, field emission displays and vacuum nano-electronic devices.

The field emission properties of Ge-dopted GaN nanowires have been investigated in theory and experiment. Ge-doping affecting field emission properties of GaN nanowires has been calculated via the basis of density functional theory (DFT). The results indicate that Ge-doped GaN nanowires have a minimum work function value of 2.37 eV when the impurity concentration is about 4.2 at.%, which is superior for application in cathode material for field emission. In addition, Ge-doped GaN nanowires have been synthesized via CVD method in our experiment. The results indicate: (1) the structure of GaN NWs is wurtzite hexagonal and the growth direction is along [0001]. (2) Ge-doped GaN nanowires possess a lower turn-on field than the pure GaN nanowires, which means Ge-doping can enhance the field emission properties of GaN nanowires, and this is consistent with the theoretical calculation results.

The electronic and optical properties of titanium (Ti) doped gallium nitride (GaN) nanowires (NWs) have been investigated using density functional theory (DFT). The donor states of near the Fermi level are mainly formed by Ti-3d orbital, and Ti-doped GaN NWs' Fermi level has an upshift compared with pure GaN NWs. The doping Ti atoms can decrease work function of GaN NWs. Moreover, the optical properties, including the complex dielectric function, optical refractive index, and absorption coefficient are discussed for radiation up to 25 eV. The results predicate that alloys exhibit a typical metallic property, in which Ti forms deep levels in the forbidden band and reduces energy gap, increases static dielectric constant and obviously red-shifts the absorption edge. The work gives a theoretical guidance for preparation of Ti-doped GaN optoelectronic nanodevices. Keywords: Ti-doped GaN NWs, Work function, Electronic and optical properties

In the original article, Fig. 3 was incorrect. The original article has been updated to display the corrected figure.

The structural, electronic, magnetic and optical properties of Ga1 − xCrxAs (x = 0, 6.25%, 12.5%) have been studied by first-principles calculations based on the HSE hybrid density functional theories. The optical properties, including the complex dielectric function, optical refractive index, extinction coefficient and absorption coefficient are discussed for radiation up to 15 eV. The results predicate that the system of Ga1 − xCrxAs exhibits typical half-metallic properties, in which Cr forms deep levels in the forbidden band and reduces the energy gap, increases static dielectric constant and obviously red-shifts the absorption edge. With the increase of the fraction of Cr, the material gradually exhibits noticeable anisotropy in the photon energy range of 0–5 eV. In addition, the p-d hybridization reduces the magnetic moment of Cr from its free space charge value of 3 μB and a smaller atomic magnetic moments of As and Ga atoms are generated. Keywords: Density functional theory (DFT), Ga1 − xCrxAs, Structural and electronic properties, Magnetic and optical properties

The roles of temperature on the structural and electronic properties of VAsVGa defects in gallium arsenide have been studied by using ab-initio molecular dynamic (MD) simulation. Our calculated results show that the relatively stable quaternary complex defect of GaAsAsGaVAsVGa can be converted from the VAsVGa complex clusters defect between 300 K and 1173 K; however, from 1173 K to 1373 K, the decomposition of the complex defect GaAsAsGaVAsVGa occurs, turning into a deep-level VAsVGa cluster defect and an isolated AsGa antisite defect, and relevant defect of GaAs is recovered. The properties of GaAsAsGaVAsVGa defect has been studied by first-principles calculations based on hybrid density functional theory. Our calculated results show that the GaAsAsGaVAsVGa belongs to EL2 deep-level defect in GaAs. Thus, we reveal that the temperature has an important effect on the microstructure of deep-level defects and defect energy level in gallium arsenide that EL2 and EL6 deep-level defects have a certain correlation, which means they could transform into each other. Controlling temperature in the growth process of GaAs could change the microstructure of deep-level defects and defect energy levels in gallium arsenide materials, whereby affects the electron transport properties of materials.

Novel gallium nitride (GaN) nanopencils have been synthesized on a silicon substrate by Ga2O3 with ammonia via the chemical vapor deposition (CVD) method. The observed morphology of GaN nanopencils is divided into two parts: the bottom is a nanowire with large diameter; the top is a nanowire with small diameter; the diameter of nanopencils decreases gradually from ~600 nm to ~200 nm along the wire axis. The formation mechanism of GaN nanopencils is a vapor–liquid–solid (VLS) mechanism. Field emission measurements show that GaN nanopencils film has high stability with a lower turn-on field of 3.5 V/µm, which is sufficient for application in field emission flat panel displays and cold electron sources in display devices. Moreover, the synthesized GaN nanopencils will facilitate flexible design of device architectures for nanoelectronics.

We investigate the defect feature ofAsGaGaAsdefect in gallium arsenide clusters in detail by using first-principles calculations based on the density functional theory (DFT). Our calculations reveal that the lowest donor level ofAsGaGaAsdefect on the gallium arsenide crystal surface is 0.85 eV below the conduction band minimum, while the lowest donor level of theAsGaGaAsdefect inside the gallium arsenide bulk is 0.83 eV below the bottom of the conduction band, consistent with gallium arsenide EL2 defect level of experimental value (Ec-0.82 eV). This suggests thatAsGaGaAsdefect is one of the possible gallium arsenide EL2 deep-level defects. Moreover, our results also indicate that the formation energies of internalAsGaGaAsand surfaceAsGaGaAsdefects are predicted to be around 2.36 eV and 5.54 eV, respectively. This implies that formation ofAsGaGaAsdefect within the crystal is easier than that of surface. Our results offer assistance in discussing the structure of gallium arsenide deep-level defect and its effect on the material.

The electronic properties of phosphorus-doped unsaturated and saturated gallium nitride (GaN) nanowires have been investigated from first-principles using the ultrasoft pseudopotential method. The results of these calculations indicate that the P impurities are enriched at the surface of gallium nitride nanowires, and that the structural symmetry of GaN nanowires is broken due to changes in the lattice parameters. When the P impurity substitutes for the Ga atom, the width of band gap increases at the Γ point, a donor impurity level appears in the band gap, and the P impurity and adjacent N atoms exists covalent interaction. Moreover, when the P impurity substitutes for the N atom, the width of the band gap decreases slightly at the Γ point, there is no obvious impurity level in the band gap, and P–Ga covalent bonds are formed, including those composed of ionic bonds. These conclusions indicate that the incorporation of P impurities can improve the field emission performance of GaN nanowires, which is consistent with the experimental results.

Helical gallium nitride nanowires were synthesized by chemical vapor deposition using a Pt catalyst. The prepared helical GaN nanowires with a single-crystalline hexagonal wurtzite structure have a coil diameter of 150–280 nm and lengths of up to tens of micrometers. The helical GaN nanowires have six equivalent 〈0\( \bar{1} \)11〉 growth directions along the [0001] axis. Field emission measurements show that helical GaN nanowire sheets possess excellent field emission properties, with a low turn-on field of ~4.5 V/μm and a high field enhancement factor of ~2,751. It is believed that this material’s excellent electron emission behavior can be attributed to its unique three-dimensional spiral structure. The growth mechanism of helical GaN nanowires has also been analyzed.

The field emission properties of the Te-doped pseudohydrogen passivated GaN nanowires have been investigated by a first principle density functional calculation. The results show that Ga atoms on the outmost-surface of GaN nanowires are more likely to be replaced by Te atoms, and two or three Te atoms are inclined to favor the nearest neighbors on the outmost-surface of GaN nanowires. Furthermore, the local electron states near the Fermi level are mainly introduced by Te atoms. The work function (WF), ionization potential (IP) and electron affinity (EA) of the Te-doped GaN nanowires decrease with the increase of the number of Te atoms. It suggests that the presence of Te atoms allows for a significant enhancement of the field emission properties. The Te-doped GaN nanowires may be used as a candidate for the future field emission electron sources.

Primary biliary cirrhosis (PBC), a chronic autoimmune liver disease, has been associated with increased incidence of osteoporosis. Intriguingly, two PBC susceptibility loci identified through genome-wide association studies are also involved in bone mineral density (BMD). These observations led us to investigate the genetic variants shared between PBC and BMD. We evaluated 72 genome-wide significant BMD SNPs for association with PBC using two European GWAS data sets (n = 8392), with replication of significant findings in a Chinese cohort (685 cases, 1152 controls). Our analysis identified a novel variant in the intron of the CLDN14 gene (rs170183, Pfdr = 0.015) after multiple testing correction. The three associated variants were followed-up in the Chinese cohort; one SNP rs170183 demonstrated consistent evidence of association in diverse ethnic populations (Pcombined = 2.43 × 10−5). Notably, expression quantitative trait loci (eQTL) data revealed that rs170183 was correlated with a decline in CLDN14 expression in both lymphoblastoid cell lines and T cells (Padj = 0.003 and 0.016, respectively). In conclusion, our study identified a novel PBC susceptibility variant that has been shown to be strongly associated with BMD, highlighting the potential of pleiotropy to improve gene discovery.

Oriented gallium nitride (GaN) nanowires grown on Pt-coated Si (1 1 1) substrates, were synthesised using the chemical vapour deposition method under different Ga sources. The characteristics of the grown GaN nanowires were investigated using scanning electron microscopy and X-ray diffraction, which found that the as-synthesised GaN nanowires of the three samples are of different orientation, and all displayed hexagonal wurtzite structures of GaN crystals. The electron field-emission properties of the three samples of GaN nanowires showed a low turn-on field of 4.5, 5.5 and 6.2 V/µm, respectively, and field enhancement factors of 1337, 2948 and 2599, respectively.

The chemical vapor deposition (CVD) process has been used to synthesize gallium nitride (GaN) nanostructures using Pt-coated n-type Si(100) as the substrate, and NH3 gas and Ga2O3 powder as the reaction agents. The surface morphologies of the prepared GaN nanostructures obtained by field emission scanning electron microscopy (FE-SEM) show a large number of GaN nanowires and nanorods on the Si substrates. The synthesized nanostructures are hexagonal as determined from XRD analysis and show a turn-on field of 5 v/μm at 10 μA/cm2.

The electronic transport properties of zigzag GaN nanotubes (n, 0) (4 ≤ n ≤ 9) have been calculated using the density functional theory and non-equilibrium Green's functions method. Firstly, the density functional theory (DFT) is used to optimize and calculate the electronic structure of GaNNTs (n, 0) (4≤n≤9). Secondly, DFT and non-equilibrium Green function (NEGF) method are also used to predict the electronic transport properties of GaNNTs two-probe system. The results showed: there is a corresponding relation between the electronic transport properties and the valley of state density of each GaNNT. In addition, the volt-ampere curve of GaNNT is approximately linear.

The electronic structures and optical properties of undoped and Al-doped GaN (AlxGa1?xN, x=0.0625, 0.125, 0.25) have been studied based on generalized gradient approximation (GGA) method of density functional theory (DFT). The differences of the electronic structures and optical properties of undoped and Al-doped GaN have been discussed in detail. The result shows: according to total density of state of undoped and Al-doped GaN, the conduction band becomes width and moves to high energy level with gradual increase concentration of Al impurity. Impurity energy band isn't found in energy band structures of AlxGa1?xN, the same as energy band structures of undoped GaN, but the band gaps gradually become wide with increase of Al impurity. Absorption spectra of undoped and Al-doped GaN of main absorption peak moves to high energy level with increase of Al impurity.