Study On Electronic Structure And Optical Properties Of Ga_x In_1-x As/GaAs Quantum Dot Molecules

The electronic structure and optical properties of Ga_xIn_1-xAs/GaAs sphere quantum dot molecules (QDMs) are investigated theoretically in the effective-mass envelope function theory. Using plane-wave expansion method, the energy levels of the electron and the hole, the transition energy, and the absorption spectra are calculated. In the calculation, the effects due to different effective masses and different finite offset of electrons and holes in different materials and different In(Ga)As composition and valence-band mixing are taken into account. We get the electron ground state energy levels, the hole ground state energy levels and the transition energy levels of QDMs ,which are all related to the Ga content, the quantum dot (QD) radius and the number of the QD in the N QDMs, besides, the electron ground state energy levels are influenced by QD position in the QDMs. Under the influence of quantum confinement effect, we find the electron ground state energy levels, the hole ground state energy levels and the transition energy levels decrease as the QD radius increases; besides, the heavy-hole ground state energy levels of 1QDM decrease obviously as the (QD) radius increases, while the light-hole ground state energy levels of 1QDM are almost unchanged when the (QD) radius is larger than about 9 nm due to the valence-band mixing and valence strain effect. When quantum dots mutual coupling, we find the hole ground state energy levels, the transition energy levels and the electron ground state energy levels (but five and six QDMs) of QDMs decrease as the number of the QD in the QDMs, due to electron ground state energy levels are influenced by QD position in the QDMs. The electron ground state energy levels and hole ground state energy levels decrease as Ga content increases, but the transition energy levels increase as Ga content increases, because as Ga content increases, the electron and hole ground state energy levels decrease slowly while band gap increase obviously; finally we get the transition energies that increase as Ga content increases. The transition energies are related to the Ga content, the radius and the number of the QD in the N QDMs, and the same transitions can be obtained by adjusting them to some values. The theoretical results play a good guiding role in the found of novel physical phenomenon and the exploration on physical properties, and have potential application value for fabrication of quantum dot devices.Moreover, we adopt structure parameters which are consistent with the experimental data to calculation absorption spectrum peak about one QD and two QD. For one QD that the radius is 12 nm, the Ga content is 0.610 when heavy-hole (light-hole) transition energies are equivalent to absorption spectrum peak. For two QD that the radius is 8 nm, the Ga content is 0.575 when heavy-hole transition energies are equivalent to absorption spectrum peak, similarly, for light-hole, the Ga content is 0.560. Thus we get quantitative explaining that one QD is larger size and higher Ga content, or two QD is smaller size and lower Ga content. The results are good agreement with the experimental explain.