Research On Electronic Structures Of Zero-Dimensional Semiconductor Materials

Nano-scaled semiconductor materials, in particular, zero-dimensional quantum dots (QDs) and quantum rings (QRs) in which the electrons and holes are confined in three dimensions possess distinct electronic and optical properties compared with bulk materials. This makes optoelectronic devices based on QDs and QRs drawing much attention in these decades. The research on zero-dimensional QDs and QRs is always the frontier in condensed matter and optoelectronics. Supported by the National High Technology Research and Development Program of China (Grant No. 2009AA03Z405), the National Natural Science Foundation of China (Grant No. 60644004), the National Natural Science Foundation of China (Grant No.60908028) and the National Natural Science Foundation of China (Grant No.60971068), this dissertation focuses on the research on electronic structures of QDs and QRs with different shapes and materials. The main productions are as follows:1. In the framework of the plane wave expansion involved in multiple-band k·p perturbation theory for zero-dimensional semiconductor materials, we adopt the Fourier transform method to determine the Hamiltonian matrix elements; explain that this method can overcome the problem that using traditional analytical integral is limited by the geometry of the QDs or QRs; and clarify the determination on Hamiltonian matrix elements with Fourier transform method.2. For InAs/GaAs QRs, we calculate the relationship between the hole energy levels in valence band and the geometric parameters such as the inner radius, outer radius, width and height of the ring, by using the analytical integral and Fourier transform method to determine the four-band k·p Hamiltonian matrix elements. The results obtained by both methods are in good consistence, which validates the Fourier transform method in dealing with the k·p Hamiltonian matrix elements. In addition, we analyze the valence band structure through four-, six- and eight-band k·p theory, and obtain the influence of the spin-orbit coupling and conduction band on the valence band. These results are instructive in the research on optoelectronic devices of InAs/GaAs QRs.3. For the irregular-shaped novel zero-dimensional structure:GaAs/AlGaAs concentric quantum double rings, the dependence of electron energy levels on the evolution of the rings is analyzed by using the Fourier transform method. The results show that when this heterostructure evolves from a single ring to concentric double rings, the change of energy levels is non-monotonic. If the uniform magnetic perpendicular to the ring plane is applied, the ground state energy of the electron will shift more than that of the hole. These results provide the precondition for the research on the transition of the electron-hole pair. 4. The strain distribution and hole bound states of type-II energy band alignment heterostructure:large lattice-mismatched GaSb/GaAs QR are calculated via the finite element method (FEM). The energies of the heavy hole and light hole are evidently different from each other due to large biaxial strain. By comparing the strain energy of truncated pyramidal GaSb/GaAs and InAs/GaAs QDs, we explain why the clear central opening of GaSb/GaAs QR forms is to release more accumulated strain energy in GaSb/GaAs QD, which is helpful in experimentally investigating the growth of GaSb/GaAs QDs or QRs.5. Adopting the FEM, the influence of the vertical and horizontal electric field on electronic structures of InAs/GaAs quantum ring molecule (QRM) and quantum dot molecule (QDM) are calculated, respectively. The results show that the electric field can effectively manipulate the electron wavefunctions in different rings or dots. In particular, for the vertical QDM non-perfectly aligned, the energy levels versus the horizon electric field lose the symmetry, which provides the theoretical approach to estimate whether the dots are vertically aligned.6. Adopting the FEM, the lowest electron energy levels corresponding to different angle momentum l of GaAs/AlGaAs two-dimensional QR versus the geometric parameters of the ring is analyzed, considering the magnetic field and the on-center donor impurity. The magnetic field changes the dependence of energy levels on the geometric parameters evidently, especially on the average radius of the ring. In addition, the magnetic field makes the energy level curves of negative angle momentum l versus the magnetic field are non-monotonic, and changes the arrangement of the energy levels. These results give instructions to further investigate the device application based on quantum ring in magnetic field.