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.
Hybrid plasmon waveguides, respectively, with metamaterial substrate and dielectric substrate are investigated and analyzed contrastively with a numerical finite element method. Basic properties, including propagation length Lp, effective mode area Aeff, and energy distribution, are obtained and compared with waveguide geometric parameters at 1.55 μm. For the waveguide with metamaterial substrate, propagation length Lp increases to several tens of microns and effective mode area Aeffis reduced by more than 3 times. Moreover, the near field region is expanded, leading to potential applications in nanophotonics. Therefore, it could be very helpful for improving the integration density in optical chips and developing functional components on a nanometer scale for all optical integrated circuits.
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.
This article puts forward a new method in calculating the band structures of low-dimensional semiconductor structures.In this study,the valence band structures of InAs/GaAs quantum ring and lens-shaped quantum dot are calculated with four-band model,in the framework of effective-mass envelope function theory.To determine the Hamiltonian matrix elements,this article develops the numerical Fourier transform method instead of the widely used analytical integral method.The valence band mixing is considered.The hole energy levels change dramatically with the geometrical parameters of the quantum ring and quantum dot.It is demonstrated that numerical Fourier transform method can be adopted in low-dimensional structures with any shape.The results of Fourier transform method are consistent with the ones of analytical integral in literature;and they are helpful for studying and fabricating optoelectronic devices.
JIA Bo-yong,YU Zhong-yuan,LIU Yu-min,TIAN Hong-da Key Laboratory of Information Photonics and Optical Communications,Ministry of Education,Beijing University of Posts and Telecommunications,Beijing 100876,China
The strain and electron energy levels of InAs/GaAs(001) quantum dots (QDs) with a GaNAs strain compensation layer (SCL) are investigated. The results show that both the hydrostatic and biaxial strain inside the QDs with a GaNAs SCL are reduced compared with those with GaAs capping layers. Moreover, most of the compressive strain in the growth surface is compensated by the tensile strain of the GaNAs SCL, which implies that the influence of the strain environment of underlying QDs upon the next-layer QDs' growth surface is weak and suggests that the homogeneity and density of QDs can be improved. Our results are consistent with the published experimental literature. A GaNAs SCL is shown to influence the strain and band edge. As is known, the strain and the band offset affect the electronic structure, which shows that the SCL is proved to be useful to tailor the emission wavelength of QDs. Our research helps to better understand how the strain compensation technology can be applied to the growth of stacked QDs, which are useful in solar cells and laser devices.
The band structures of rectangular GaN/AlGaN quantum wires are modeled by using a parabolic effective-mass theory.The absorption coefficients are calculated in a contact-density matrix approach based on the band structure.The results obtained indicate that the peak absorption coefficients augment with the increase of the injected carrier density,and the optical gain caused by interband transition is polarization anisotropic.For the photon energy near 1.55 eV,we can obtain relatively large peak gain.The calculations support the previous results published in the recent literature.
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.
