Narrow Results

This paper presents a finite element method for calculating the strain distribution, piezoelectric effects and their influences on the electronic structure of self-organized InAs/GaAs quantum dots. The models used for strain calculations are based on the continuum elastic theory, which is capable of treating the quantum dot of arbitrary shapes. A truncated pyramid shaped quantum dot model including the wetting layer is adopted in this work. The electronic energy levels of the InAs/GaAs systems are calculated by solving the three-dimension effective mass Schrödinger equation including the influences on the modification of conduction band edge due to the strain and piezoelectricity. The calculated results indicate that both strain and piezoelectric effects should be considered, especially in treating the electronic structure and optical characteristics for device applications.

A systematic investigation is given about the effects of the longitudinal and transverse periodic distributions on the elastic strain field. The results show that the influences of the longitudinal and transverse period on the strain field are just opposite, especially for the path along the center-axis of the quantum dots. In the proper conditions, the influence of periodicity on strain field distribution can be partly eliminated. The results demonstrate that when calculating the effect of the strain field on the electronic structure, one must take the quantum dots periodic distribution into account. It is unsuitable to use the isolated quantum dot model in simulating the strain field and evaluate the influence on electronic structure.

This paper presents a detailed investigation of the effects of piezoelectricity, spontaneous polarization and charge density on the electronic states and the quasi-Fermi level energy in wurtzite-type semiconductor heterojunctions. This has required a full solution to the coupled Schrödinger–Poisson–Navier model, as a generalization of earlier work on the Schrödinger–Poisson problem. Finite-element-based simulations have been performed on a AlN/GaN quantum well by using both one-step calculation as well as the self-consistent iterative scheme. Results have been provided for field distributions corresponding to cases with zero-displacement boundary conditions and also stress-free boundary conditions. It has been further demonstrated by using four case study examples that a complete self-consistent coupling of electromechanical fields is essential to accurately capture the electromechanical fields and electronic wavefunctions. We have demonstrated that electronic energies can change up to approximately 0.5 eV when comparing partial and complete coupling of electromechanical fields. Similarly, wavefunctions are significantly altered when following a self-consistent procedure as opposed to the partial-coupling case usually considered in literature. Hence, a complete self-consistent procedure is necessary when addressing problems requiring more accurate results on optoelectronic properties of low-dimensional nanostructures compared to those obtainable with conventional methodologies.