Capping of InAs/GaAs Quantum Dots for GaAs Based Lasers
Nowadays, self-assembled InAs quantum dots grown on GaAs substrates are intensively studied due to their potential applications: quantum dot ensembles are employed in laser active regions and mid-infrared detectors, single quantum dots have a potential for application in memories, two-level information processing or single photon sources (Henini& Bugajski, 2005; Mowbray& Skolnick, 2005; Battacharya, 2007).
Combined vertically correlated InAs and GaAsSb quantum dots separated by triangular GaAsSb barrier
The aim of this work is to offer new possibilities for quantum dot (QD) band structure engineering, which can be used for the design of QD structures for optoelectronic and single photon applications. Two types of QDs, InAs and GaAsSb, are combined in self assembled vertically correlated QD structures. The first QD layer is formed by InAs QDs and the second by vertically correlated GaAsSb QDs. Combined QD layers are separated by a triangular GaAsSb barrier. The structure can be prepared as type-I, with both electrons and holes confined in InAs QDs, exhibiting a strong photoluminescence, or type-II, with electrons confined in InAs QDs and holes in GaAsSb QDs. The presence of the thin triangular GaAsSb barrier enables the realization of different quantum level alignment between correlated InAs and GaAsSb QDs, which can be adjusted by structure parameters as type-I or type-II like for ground and excited states separately. The position of holes in this type of structure is influenced by the presence of the tr...
In search of optimum chest radiography techniques.
A nation-wide study of chest radiography in Sweden had previously revealed a large variation in the physical and technical factors involved, in particular the radiation dose. In this study the image quality could not be assessed unambiguously. The aim of the present study was to try to establish a correlation between visual grading of radiographs and physical and technical factors in order to find the optimum chest X-ray system. The physical and technical performance of 24 chest units was evaluated. Radiographs were taken of an anthropomorphic chest phantom supplied with test structures simulating various pathologies. Image quality was assessed by visual grading analysis of the radiographs. The physical and technical parameters of the units rated best were used to exemplify good radiographic practice. The results were in agreement with the recommendations issued by the Commission of the European Communities (CEC). It was also shown that low radiation dose is compatible with high-quality radiographic imaging of the chest.