A site-controlled quantum dot system offering both high uniformity and spectral purity

In this paper we report on the optical properties of site controlled InGaAs dots with GaAs barriers grown in pyramidal recesses by metalorganic vapour phase epitaxy. The inhomogeneous broadening of excitonic emission from an ensemble of quantum dots is found to be unusually narrow, with a standard deviation of 1.19 meV, and spectral purity of emission lines from individual dots is found to be very high (18-30 ueV), in contrast with other site-controlled systems.Comment: 12 pages, 3 figure

Semiconductor nanostructures engineering: Pyramidal quantum dots

Pyramidal quantum dots (QDs) grown in inverted recesses have demonstrated over the years an extraordinary uniformity, high spectral purity and strong design versatility. We discuss recent results, also in view of the Stranski-Krastanow competition and give evidence for strong perspectives in quantum information applications for this system. We examine the possibility of generating entangled and indistinguishable photons, together with the need for the implementation of a, regrettably still missing, strategy for electrical control

A study of nitrogen incorporation in pyramidal site-controlled quantum dots

We present the results of a study of nitrogen incorporation in metalorganic-vapour-phase epitaxy-grown site-controlled quantum dots (QDs). We report for the first time on a significant incorporation (approximately 0.3%), producing a noteworthy red shift (at least 50 meV) in some of our samples. Depending on the level of nitrogen incorporation/exposure, strong modifications of the optical features are found (variable distribution of the emission homogeneity, fine-structure splitting, few-particle effects). We discuss our results, especially in relation to a specific reproducible sample which has noticeable features: the usual pattern of the excitonic transitions is altered and the fine-structure splitting is suppressed to vanishing values. Distinctively, nitrogen incorporation can be achieved without detriment to the optical quality, as confirmed by narrow linewidths and photon correlation spectroscopy

Anisotropic Confinement, Electronic Coupling and Strain Induced Effects Detected by Valence-Band Anisotropy in Self-Assembled Quantum Dots

A method to determine the effects of the geometry and lateral ordering on the electronic properties of an array of one-dimensional self-assembled quantum dots is discussed. A model that takes into account the valence-band anisotropic effective masses and strain effects must be used to describe the behavior of the photoluminescence emission, proposed as a clean tool for the characterization of dot anisotropy and/or inter-dot coupling. Under special growth conditions, such as substrate temperature and Arsenic background, 1D chains of In0.4Ga0.6 As quantum dots were grown by molecular beam epitaxy. Grazing-incidence X-ray diffraction measurements directly evidence the strong strain anisotropy due to the formation of quantum dot chains, probed by polarization-resolved low-temperature photoluminescence. The results are in fair good agreement with the proposed model

A light-hole exciton in a quantum dot

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Optical polarization anisotropy and hole states in pyramidal quantum dots

The authors present a polarization-resolved photoluminescence study of single semiconductor quantum dots (QDs) interconnected to quantum wires, measured both in a top geometry, and in a less conventional cleaved-edge geometry. Strong polarization anisotropy is revealed for all observed transitions, and it is deduced that closely spaced QD hole states exhibit nearly pure heavy-or light-hole character. These effects are attributed to the large aspect ratio of the dot shape. (c) 2006 American Institute of Physics

Excited excitonic states observed in semiconductor quantum dots using polarization resolved optical spectroscopy

We present results on the polarization-resolved photoluminescence emitted from InGaAs/AlGaAs single quantum dots (QDs) grown in inverted tetrahedral pyramids. The emitted light was detected for two mutually perpendicular linear polarization directions in the less conventional cleaved-edge geometry, in addition to the standard top-emission geometry. Whereas the in-plane linear polarization was isotropic, as a consequence of the high symmetry of the system, we found a strong polarization anisotropy of the edge-emitted light revealing QD states of predominantly heavy- or light-hole character. By temperature control of the charge state, several neutral and charged light-hole like exciton complexes were identified. In particular, a biexciton showing a twofold radiative recombination path, leading to two nearly perpendicularly polarized emission multiplets, was identified. These results are also of technological relevance for any design of optoelectronic QD-integrated devices

ASPECTOS EPIDEMIOLÓGICOS DE ENFERMIDADES CIRÚRGICAS DO APARELHO GENITAL DE TOUROS EM UMA POPULAÇÃO DE 12.320 REPRODUTORES (1982-2007) NO ESTADO DE GOIÁS, BRASIL EPIDEMIOLOGICAL ASPECTS OF SURGICAL DISEASES OF THE GENITAL TRACT IN A POPULATION OF 12.320 BREEDING BULLS (1982-2007) IN THE STATE OF GOIAS, BRAZIL

<span><span><span>O aparelho genital do touro pode ser acometido por enfermidades que resultam em impotência <em>coeundi</em>, levando à queda na eficiência reprodutiva. Aspectos anatômicos, raciais e manejo são considerados fatores predisponentes de injúrias à genitália. Neste estudo, catalogaram-se 12.320 touros entre 1982 e 2007, sendo que, destes, 898 (7,29%) eram portadores de alguma enfermidade cirúrgica no aparelho reprodutor, diagnosticados pelo exame clínico específico da genitália ou por meio do teste de capacidade de serviço. Concomitantemente, aplicou-se questionário para obtenção de informações relacionadas à epidemiologia das enfermidades genitais. Dos 898 touros enfermos, <span><p align="justify">741 (82,52%) eram zebuínos, 133 (14,81%) taurinos e 24 (2,67%) mestiços. Observou-se que 570 (63,5%) possuíam idade igual ou superior a 60 meses, 220 (24,5%) entre 40 e 60; e 108 (12,0%) inferior a 40 meses. Dentre as enfermidades diagnosticadas, registraram-se 728 (81%) casos de acropostite-fimose, 46 (5,20%) desvios penianos, 23 (2,60%) fibropapiloma de glande, 14 (1,60%) abscessos prepuciais e 11 (1,20%) fraturas penianas. Dos 417 produtores rurais visitados, 256 (61,50%) efetuavam, empiricamente, tratamento das enfermidades, ignorando a importância do diagnóstico. Concluiu-se que o manejo e a característica racial foram os principais fatores predisponentes relacionados à etiopatogenia das enfermidades do aparelho reprodutor.</p><span><p align="justify">PALAVRAS-CHAVES: Bovino, epidemiologia, reprodução.</p></span></span></span></span></span> <span>  <p align="justify">The genital tract of bulls might be affected by diseases that result in <em>coeundi</em> impotence leading to decrease of reproductive efficiency. Anatomic, breed and handling aspects are considered predisponent factors to genital injuries. In this study, it was considered 12,320 bulls evaluated between 1982 and 2007. From these, 898 (7.29%) bulls had some reproductive tract disease corrected surgically, diagnosed by specific clinical examination of the genitalia or service capacity test. At the same time, questionnaire was applied in order to obtain information related to genital diseases epidemiology. From 898 ill bulls, 741 (82.52%) were <em>Bos indicus</em>, 133 (14.81) were<em> Bos taurus</em> and 24 (2.67%) were crossbred bulls. It was observed that 570 (63.50%) were ≥60 months-old, 220 (24.5%) were between 40 and 60 months-old and 108 (12.0%) were ≤40 months-old. Among the diagnosed diseases, independent of breed, age and handling, it was identified 728 (81%) cases of acropostitis-fimosis, 46 (5.20%) penis deviation, 23 (2.60%) gland fibropapilloma, 14 (1.60%) preputial abscesses and 11 (1.20%) penile fractures. From 417 visited farms, 256 (61.50%) treated the disease empirically, ignoring previous diagnosis. Thus, it can be concluded that handling and breed characteristics were the main predisposing factors related for the etiopathogeny of reproductive tract diseases.</p><span><p align="justify">KEY WORDS: Bovine, epidemiology, reproduction.</p></span></span&gt