The couple electronic state of the stack quantum dots by axial- symmetrically finite element analysis

摘要

Semiconductor quantum dots have been of major interest in recent years. This has largely been simulated by progress in quantum dot growth technology, whereby self-organized quantum dots array can be fabricated by MBE and MOCVD facilities using Stranski Krastanow growth mode. Quantum does material has achieved broad applications in optoelectronic devices and quantum information fields because of the unique 3D electron confinement. However, a good understanding about the electronic, excitonic and optoelectronics properties of the quantum materials are very important in fabrication nanostructure devices based on quantum dots. Based on the 1-band effective-mass theory, a finite element numerical technique is developed to calculate the electronic structure of truncated conical shaped InAs GaAs vertical aligned quantum dot molecular, including the wetting layer. Using the axis-symmetry model, the 3D effective-mass Schrodinger equation with step potential barrier can be reduced to a 2D problem by separating variable technique, which greatly reduced the calculation cost. Form the calculated results, we found that the coupling effects is obviously when the separation distance is in the range of the less than 10nm. The wave functions will exhibits large probability in the region between the quantum dots. In order to consider the effect of the distance between the two layers of quantum dots on the electronic state coupling, we calculated the results when the distance is 6nm, llnm, 14nm and 17nm. The ground state, the second excited and the highest excited state will lower its energy with decreasing the distance between the quantum dots, but the second excited state will increase its energy. With increasing the distance between the two quantum dots, the coupling effect will become weaker, and for the ground state, the wave function distribution will tend to localized only in one of the quantum dot, the energy become something degenerate. The calculated results show that the ground state and the first excited state are degenerate. With decreasing of the distance, the degenerate states are broken, and the energy levels are separated. In our simulations, the strain effects are ignored. In the future woks, strain should be taken in to account as an easy way. The calculated results can help us to examine optoelectronic properties of the semiconductor nanostructure based on multi sheet of quantum dots with wetting layers.