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.
The optimal top structure of a nanowire quantum emitter single photon source is significant in improving performance. Based on the axial symmetry of a cylindrical nanowire,this paper optimizes the top profile of a nanowire for the maximum forward emission by combining the geometry projection method and the finite element method.The results indicate that the nanowire with a cambered top has the stronger emission in the forward direction,which is helpful to improve the photon collection efficiency.
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.
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.
This article deals with the strain distributions around GaN/AlN quantum dots by using the finite element method. Special attention is paid to the influence of Al0.2Ga0.8N strain-reducing layer on strain distribution and electronic structure. The numerical results show that the horizontal and the vertical strain components are reinforced in the GaN quantum dot due to the presence of the strain-reducing layer, but the hydrostatic strain in the quantum dot is not influenced. According to the deformation potential theory, we study the band edge modifications and the piezoelectric effects. The result demonstrates that with the increase of the strain reducing layer, the transition energy between the ground state electron and the heavy hole increases. This result is consistent with the emission wavelength blue shift phenomenon observed in the experiment and confirms that the wavelength shifts toward the short wavelength range is realizable by adjusting the structure-dependent parameters of GaN/AlN quantum dot.
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
