Lattice systems quantum dots

The relative solubility of inorganic salts can be used to prepare more complex structures by such methods and examples indude CdS/ZnS [24], CdSe/AgS [25] HgS/CdS [26], PbS/CdS [27, 28], CdS/HgS [29], ZnS/CdSe [30] and ZnSe/CdSe [31] particles. The main constraints on the production of such structures involve the relative solubility of the solids and lattice mismatches between the phases. The preparation of quantum dot quantum well systems such as CdS/HgS/CdS [32, 33], has also been reported, in which a HgS quantum well of 1-3 monolayers is capped by 1-5 monolayers of CdS. The synthesis grows less soluble HgS on CdS (5.2 nm) by ion-replacement. The solubility products of CdS and HgS are 5 X 10 and 1.6 x 10 respectively. The authors reported fluorescence measurements in which the band edge emission for CdS/HgS/CdS is shifted to lower energy values with increasing thickness of the HgS well [33]. 

A quantum dot is made from a semiconductor nanostructure that confines the motion of conduction band electrons, valence band holes, or excitons (bound pairs of conduction band electrons and valence band holes) in all three spatial directions. A quantum dot contains a small finite number (of the order of 1 to 100) of conduction band electrons, valence band holes, or excitons, that is, a finite number of elementary electric charges (Scheme 16.2). The reason for the confinement is either the presence of an interface between different semiconductor materials (e.g. in coie-sheU nanocrystal systems) or the existence of the semiconductor surface (e.g. semiconductor nanocrystal). Therefore, one quantum dot or numerous quantum dots of exactly the same size and shape have a discrete quantized energy spectrum. The corresponding wave functions are spatially localized within the quantum dot, but they always extend over many periods of the crystal lattice (5). 

When Sq < 2%, quantum dots are not formed, and the growth of heterostructures proceeds by the layer-by-layer growth mechanism. At very large values of the mismatch parameter the growth follows the Volmer-Weber mechanism. Then the critical wetting layer thickness is less than one monolayer, and the formation of three-dimensional islands occurs directly on the substrate surface. An example of such a system is the InAs/Si system, wfiere = 10.6%. In a system of silicon and chromium the lattice... 

In the fabrication of semiconductors, the composition of ternary and quaternary alloys can be strongly influenced by factors like the temperature and the duration of the annealing processes. For example, the sulfur content in CdSSe quantum dots increases with increasing temper temperature [48]. In the case of superlattices with very thin layer thicknesses, unwanted ternary or quaternary alloys can be formed by diffusion of the ions into the adjacent layer. Because of this, it is necessary to prove the material composition of the alloys after the growth. The behavior of the vibrational properties of a system with an incorporated element B in the crystal lattice AC is similar to the problem of the impurities The element B causes a distortion of the lattice because of the difference in the masses and, hence, of the appearance of new modes. With increasing... 

We previously described some methods used to obtain an array of unstrained Ge quantum dots (QD) on heteroepitaxial ZnSe layers. The examined ZnSe/Ge heterosystem is characterized by similar type of the lattice and small mismatch value for their constants, w 0.2%, which excludes occurrence of the mechanical stress in the substrate-nanoobject system When studying the islets formation in this system, we observed a low-temperature recrystallization of Ge - the transition from the amorphous state to the polycrystalline one, and then into the continuous epitaxial layer (Suprun Fedosenko, 2007). The temperature was significantly below the melting temperature of the bulk material. Later we conducted experiments in situ for direct observation of this process using RHEED and XPS methods, and the results were analyzed in terms of BOLS model. 

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