By three-dimensional kinetic Monte Carlo simulations, the effects of the temperature, the flux rate, the total coverage and the interruption time on the distribution and the number of self-assembled InAs/GaAs(001) quantum dot(QD) islands are studied, which shows that a higher temperature, a lower flux rate and a longer growth time correspond to a better island distribution. The relations between the number of islands and the temperature and the flux rate are also successfully simulated. It is observed that for the total coverage lower than 0.5 ML, the number of islands decreases with the temperature increasing and other growth parameters fixed and the number of islands increases with the flux rate increasing when the deposition is lower than 0.6 ML and the other parameters are fixed.
A nonlinear hybrid plasmonic slot waveguide composed of periodically poled lithium niobate(PPLN)and two separated silver films is investigated.The e?ective refractive index,propagation length,and energy confinement of the hybrid anti-symmetric mode in this waveguide are calculated using the structure parameters at the fundamental wavelength ofλ=1550 nm and its second harmonic(SH)λ=775 nm.Through the above indices,coupling e?ciency(maximum SH conversion e?ciency during propagation)and peak position(propagation location of the conversion e?ciency)of SH generation are analyzed.Finally,higher conversion e?ciency can be achieved at a shorter propagation distance by changing the waveguide into a tapered structure.
This paper presents a finite element calculation for the electronic structure and strain distribution of self-organized InAs/GaAs quantum rings.The strain distribution calculations are based on the continuum elastic theory.An ideal three-dimensional circular quantum ring model is adopted in this work.The electron and heavy-hole energy levels of the InAs/GaAs quantum rings are calculated by solving the three-dimensional effective mass Schro¨dinger equation including the deformation potential and piezoelectric potential up to the second order induced by the strain.The calculated results show the importance of strain and piezoelectric effects,and these effects should be taken into consideration in analysis of the optoelectronic characteristics of strain quantum rings.
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 k.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.
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.
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.
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.
In this paper, the kinetic Monte Carlo simulations of the self-assembly quantum rings (QRs) based on the substrate engineering, which is related to the eventual shape of the formed quantum ring, are implemented. According to the simulation results, the availability of the QR with tunable size and the formation of smooth shape on the ideal flat substrate are checked. Through designing the substrate engineering, i.e., changing the depth, the separation and the ratio between the radius and the height of the embedded inclusions, the position and size of QR can be controlled and eventually the growth strategy of optimizing the self-assembly QRs is accomplished.
Piezoelectric effects and electronic structures of InAs/GaAs quantum dots grown along (111) and (011) directions are investigated in this paper.The finite element method is used.Electronic energy levels are calculated by solving the three-dimensional effective mass Schrdinger equation including a strain modified confinement potential and piezoelectric effects.The difference in electronic structure between quantum dots grown along the (111) direction and the (011) direction are compared.The cubic and truncated pyramidal shaped quantum dots are adopted.
The strain distribution and electronic structures of the InAs/GaAs quantum ring molecule are calculated via the finite element method.In our model,three identical InAs quantum rings are aligned vertically and embedded in the cubic GaAs barrier.Considering the band edge modification induced by the strain,the electronic ground state and the dependence of ground state energy on geometric parameters of the quantum ring molecule are investigated.The change of localization of the wavefunction resulting from the applied electric field along the growth direction is observed.The ground state energy decreases as the electric field intensity increases in a parabolic-like mode.The electric field changes the monotonic dependence of the energy level on the inter-ring distance into a non-monotonic one.However,the electric field has no effect on the relationships between the energy level and other geometric parameters such as the inner radius and outer radius.
JIA BoYong,YU ZhongYuan,LIU YuMin,YAO WenJie,YE Han & FENG Hao Key Laboratory of Information Photonics and Optical Communications(Beijing University of Posts and Telecommunications),Ministry of Education,Beijing 100876,China
