Authors: Karel Král, Petr Zdenĕk
65
Authors: Dj. Veljković, M. Tadić, F.M. Peeters
Abstract: The intersublevel absorption in n-doped InAs/GaAs self-assembled quantum-dot
molecules composed of three quantum dots is theoretically considered. The transition matrix elements and the transition energies are found to vary considerably with the spacer thickness. For s polarized light, decreasing the thickness of the spacer between the dots brings about crossings between the transition matrix elements, but the overall absorption is not affected by the variation of the spacer thickness. For p-polarized light and thick spacers, there are no available transitions in the single quantum dot, but a few of them emerge as a result of the electron state splitting in the stacks of coupled quantum dots, which leads to a considerable increase of the transition matrix elements, exceeding by an order of magnitude values of the matrix elements for s-polarized light.
37
Authors: Subindu Kumar, Dipankar Biswas, Tapas Das
Abstract: In recent years there have been extensive studies on III-V semiconductor quantum dots
(QDs). In this paper we have formulated the absorption spectra of a realistic QD system with dot
size distribution described by a Gaussian function. The dots were approximated as cubic boxes
having finite potentials at the boundaries. The effects of size non uniformity on the optical
absorption spectra of a realistic QD system was analyzed and the results have been compared with
ideal dots having infinite potentials at the boundaries.
59
Authors: Wei Cui, Chong Wang, Yu Yang
Abstract: The solar energy is the most promising energy to solve energy crisis and environmental problem. Quantum dot can be applied to solar cells in two structures of QDSC to improve the energy conversion efficiency. The two structures are p-i-n type QDSC and quantum dots sensitized solar cells. The energy conversion efficiency of p-i-n type QDSC may increase up to 45%. Both CdSe and CdS quantum dot can be used as the sensitizer of the QDSSC and each of them has its demerits and merits, but the conversion efficiency of QDSSC is low if they were used respectively. Thus, in order to overcome their demerits respectively, we could try to combine their merits. QDSC is the most promising technique to solve the problems of solar cell. But before large-scale application their efficiency and stability should be improved.
693
Authors: Sib Krishna Ghoshal, M.R. Sahar, R. Arifin, M.S. Rohani, K. Hamzah
Abstract: Tuning the visible emission of Si nanomaterials by modifying their size and shape is one of the key issue in optoelectronics. The observed optical gain in Si-nanoclusters (NCs) has given further impulse to nanosilicon research. We develop a phenomenological model by combining the effects of surface passivation, exciton states and quantum confinement (QC). The size and passivation dependent band gap, oscillator strength, radiative lifetime and photoluminescence (PL) intensity for NCs with diameter ranging from 1.0 to 6.0 nm are presented. By controlling a set of fitting parameters, it is possible to tune the optical band gap, PL peak and intensity. In case of pure clusters, the band gap is found to decrease with increasing NC size. Furthermore, the band gap increases on passivating the surface of the cluster with hydrogen and oxygen respectively in which the effect of oxygen is more robust. Both QC and surface passivation in addition to exciton effects determine the optical and electronic properties of silicon NCs. Visible luminescence is due to radiative recombination of electrons and holes in the quantum-confined NCs. The role of surface states on the band gap as well as on the HOMO-LUMO states is also examined and a correlation is established. Our results are in conformity with other observations. The model can be extended to study the light emission from other nanostructures and may contribute towards the development of Si based optoelectronics.
308
