Donor-bound electron states in a two-dimensional quantum ring under uniform magnetic field

The electron states in a two-dimensional GaAs/AlGaAs quantum ring are theoretically studied in effective mass approximation. On-centre donor impurity and uniform magnetic field perpendicular to the ring plane are taken into account. The energy spectrum with different angular momentum changes dramatically with the geometry of the ring. The donor impurity reduces the energies with an almost fixed value; however, the magnetic field alters energies in a more complex way. For example, energy levels under magnetic field will cross each other when increasing the inner radius and outer radius of the ring, leading to the fact that the arrangement of energy levels is distinct in certain geometry of the ring. Moreover, energy levels with negative angular momentum exhibit the non-monotonous dependence on the increasing magnetic field.     

First-principles study of electronic and optical properties in wurtzite Zn1-xCuxO

We perform a first-principles simulation to study the electronic and optical properties of wurtzite Zn1 xCuxO.The simulations are based upon the Perdew-Burke-Ernzerhof form of generalised gradient approximation within the density functional theory.Calculations are carried out in different concentrations.With increasing Cu concentration,the band gap of Zn1 xCuxO decreases due to the shift of valence band.The imaginary part of the dielectric function indicates that the optical transition between O 2p states in the highest valence band and Zn 4s states in the lowest conduction band shifts to the low energy range as the Cu concentration increases.Besides,it is shown that the insertion of Cu atom leads to redshift of the optical absorption edge.Meanwhile,the optical constants of pure ZnO and Zn0.75Cu0.25O,such as loss function,refractive index and reflectivity,are discussed.     

Electronic Structure and Optical Properties of Zinc-Blende InxGa1-xNyAs1-y by a First-Principles Study

Electronic structure and optical properties of the zinc-blende In_xGa_{1 - x}N_yAs_1-y system are calculated from the first-principles. Some relative simulations are performed using CA-PZ form of local density approximation in the framework of density functional theory. The supercell of intrinsic GaAs is calculated and optimized by using different methods, and the LDA-CA-PZ gives the most stable structure. The band gap of In_xGa_{1 - x}As tends to decrease with the increasing In concentration. For the case of In_0.0625Ga_0.9375N_yAs_{1 -y}, the band gap will show slight difference when N concentration is larger than 18.75%. The optical transition of In dopant in GaAs exhibits a red shift, while it is a blue shift for the N dopant in InGaAs. Besides, dielectric function, reflectivity, refractive index and loss function in different doping model of In_xGa_{1 - x}N_yAs_{1 - y} are also discussed.     

Electronic and optical properties of GaN/AlN quantum dots with adjacent threading dislocations

We present a theory to simulate a coherent GaN QD with an adjacent pure edge threading dislocation by using a finite element method. The piezoelectric effects and the strain modified band edges are investigated in the framework of multi-band $\bm k\cdot \bm p$ theory to calculate the electron and the heavy hole energy levels. The linear optical absorption coefficients corresponding to the interband ground state transition are obtained via the density matrix approach and perturbation expansion method. The results indicate that the strain distribution of the threading dislocation affects the electronic structure. Moreover, the ground state transition behaviour is also influenced by the position of the adjacent threading dislocation.     

Electronic structures of stacked layers quantum dots: influence of the non-perfect alignment and the applied electric field

Electronic structures of the artificial molecule comprising two truncated pyramidal quantum dots vertically coupled and embedded in the matrix are theoretically analysed via the finite element method.When the quantum dots are completely aligned,the electron energy levels decrease with the horizontally applied electric field.However,energy levels may have the maxima at non-zero electric field if the dots are staggered by a distance of several nanometers in the same direction of the electric field.In addition to shifting the energy levels,the electric field can also manipulate the electron wavefunctions confined in the quantum dots,in company with the non-perfect alignment.     

The equilibrium composition in GexSi1-x/Si self-assembled alloy quantum dot

<正>The equilibrium composition in strained quantum dot is the result of both elastic relaxation and chemical mixing effects,which have a direct relationship to the optical and electronic properties of the quantum-dot-based device.Using the method of moving asymptotes and finite element tools,an efficient technique has been developed to compute the composition profile by minimising the Gibbs free energy in self-assembled alloy quantum dot.In this paper,the composition of dome-shaped Ge_xSi_(1-x)/Si quantum dot is optimized,and the contribution of the different energy to equilibrium composition is discussed.The effect of composition on the critical size for shape transition of pyramid-shaped GeSi quantum dot is also studied.     

Tunable Dual-Wavelength Fiber Laser in a Novel High Entropy van der Waals Material

Fiber lasers with different net dispersion cavity values can produce some types of solitons, and rich nonlinear dynamics phenomena can be achieved by selecting different saturable absorbers. A new layered high-entropy van der Waals material(HEX)(Mn,Fe,Co,Ni)PS₃ was selected as a saturable absorber to achieve a high-power laser output of 34 m W. In addition, the wavelength can be dynamically tuned from 1560 nm to 1531 nm with significant dual-wavelength phenomena at 460 fs pulse durati...