We report a comprehensive discussion of quantum interference effects due to the finite structure of excitons in quantum rings and their first experimental corroboration observed in the optical recombinations. Anomalous features that appear in the experiments are analyzed according to theoretical models that describe the modulation of the interference pattern by temperature and built-in electric fields.PACS numbers: 71.35.Ji, 73.21.La, 78.20.Ls, 78.67.Hc The nanoscale ring structures, or quantum rings (QRs), have attracted the interest of the scientific community due to their unique rotational symmetry and the possibility to verify quantum mechanical phenomena.[1, 2, 3] Among these, the study of Aharonov-Bohm (AB)-like effects has gained a significant impetus, [4,5,6] and these efforts have gone beyond the original discussion of the AB interpretation on the nature of electromagnetic potentials and their role in quantum mechanics. [7] It is reasonable to say that the study of coherent interference occurring in transport properties of nanoscopic QRs, as proposed in Ref. 7 encounters, at the moment, serious scale limitations which has encouraged the search for optical implications associated to AB-effects.These endeavors applied to nanoscopic QRs do not strictly meet the original conditions for the ABconfiguration since the carriers are confined within regions with finite values of magnetic field. However, we still consider an observed effect as of AB-type if it can be explained assuming that the magnetic field is ideally concentrated in the middle of the QRs, i. e., when such effect comes essentially from potential vector-mediated quantum interference. As also considered in Ref. 8, in stationary systems this interference is generally reflected in a boundary condition and it is not as explicit as in the famous picture of an AB scattering situation.In this work we consider AB-interference in excitonic states as proposed theoretically in Refs. 9, 10, 12. Instead of looking only at the oscillatory dependence on magnetic flux of the electron-hole (e − h) recombination energy during photo-luminescence (PL), we also consider the excitonic oscillator strength whose oscillatory behavior reflects directly the changes in the exciton wavefunction as the magnetic flux increases. A similar experimental work was reported in Ref. 6 for type-II QRs, however, here we study type-I systems where both electron and hole move in the ring so that the correlation between them is crucial to the oscillatory behavior found in the PL integrated intensity. The samples studied here were grown using a RIBER 32P solid-source molecular beam epitaxy chamber and the QRs were grown using the following procedure. A 0.5 µm GaAs buffer layer was grown on semi-insulating (100) GaAs substrates at 580• C, after oxide desorption. Then, it was followed by 2.2 ML of InAs and the formation of quantum dots (QDs) at 520• C. The dots were obtained using the Stranski-Krastanov growth mode. Cycles of 0.14 ML of InAs plus a 2 s interruption under As 2 flux were r...

Here, we report the synthesis and structural characterization of high-quality Zn3P2 nanowires via chemical vapour deposition. Structural and morphological characterization studies revealed a reliable growth process of long, uniform, and single-crystalline nanowires. From temperature dependent transport and photoluminescence measurements, we have observed the contribution of different acceptor levels (15, 50, 70, 90, and 197 meV) to the conduction mechanisms. These levels were associated with zinc vacancies and phosphorous interstitial atoms which assigned a p-type character to this semiconductor. From time resolved photoluminescence experiments, a 91 ps lifetime decay was found. Such a fast lifetime decay is in agreement with the exciton transition along the bulk emission from high quality crystalline nanowires.

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The instability during the growth and processing of epitaxial GeSn layers with high Sn molar fraction and high compressive strain is still to be fully studied. In this work, the relationship among strain relief, dislocations, and Sn outdiffusion in GeSn layers with a Sn content of ∼9 atom % was studied as a function of pre-existing misfit/threading dislocation (MD/TD) density and annealing time at 300 °C. For a GeSn epilayer strained to a Ge-on-Si virtual substrate (Ge-VS), an increase of strain relief by a factor of ∼2 is observed after 2 h of annealing, without a significant effect on strain relaxation for a more prolonged temperature treatment. This is explained by the limited propagation or elongation of pre-existing MDs at the interface of GeSn/Ge-VS. The onset of Sn outdiffusion and the appearance of segregation spots are observed for the GeSn epilayers with significant strain relaxation (≥50%) before annealing, for which the density of MDs ≥ 2 × 10 5 cm −1 . This is explained by generation of high-density MDs/TDs acting as preferential sites for Sn accumulation during the growth of the GeSn layer. This work explicitly provides an understanding that dislocation engineering is one of the key factors for the stability and performance of GeSn semiconductors.

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A shape-selective preparation method was used to obtain highly crystalline rod-, needle-, nut-, and doughnut-like ZnO morphologies with distinct particle sizes and surface areas.

Present theoretical and experimental work provides an in-depth understanding of the morphological, structural, electronic, and optical properties of hexagonal and monoclinic polymorphs of BiPO 4 . Herein, we demonstrate how microwave irradiation induces the transformation of the hexagonal to a monoclinic phase one in a short period of time and thus, the photocatalytic performance of BiPO 4 . To complement and rationalize the experimental results, first-principle calculations have been performed within the framework of the density functional theory. This was aimed at obtaining the geometric, energetic and structural parameters as well as vibrational frequencies; further, electronic properties (band structure diagram and density of states) of the bulk and the corresponding surfaces of both hexagonal and monoclinic surfaces of BiPO 4 were also acquired. A detailed characterization of the low vibrational modes of both hexagonal and monoclinic polymorphs is key in explaining the irreversible phase transformation from hexagonal to monoclinic. Based on the calculated values of the surface energies, a map of the available morphologies of both phases was obtained by using the Wulff construction and compared with the observed SEM images. The BiPO 4 crystals obtained after 16-32 min of microwave irradiation provided excellent photodegradation of Rhodamine B under visible light irradiation. This enhancement was found to be related to the surface energy and the types of clusters formed on the exposed surfaces of the morphology. These findings provide details of the 3 hexagonal to monoclinic phase transition in BiPO 4 during microwave irradiation; further, the results will assist in designing electronic devices with higher efficiency and reliability.

Cd(1-x)Mn(x)S nanoparticles (NPs) were successfully grown in a glass matrix and investigated by optical absorption (OA), magnetic circularly polarized photoluminescence (MCPL) measurements, and magnetic force microscopy (MFM). The room temperature OA spectra have revealed the formation of two groups of Cd(1-x)Mn(x)S NPs with different sizes: bulk-like nanocrystals (NCs) and quantum dots (QDs). The MCPL spectra were recorded at 2.0 K with several magnetic fields up to 15 T, allowing a detailed comparison between the degrees of circular polarization of the two groups of NPs. The different behaviours of magneto-optical properties of bulk-like NCs and QDs were explained by taking into account a considerable alteration of exchange interaction between the carrier spins and the substitutional doping magnetic ions incorporated into the NPs. As a main result, we have demonstrated that self-purification is the dominant mechanism that controls the doping in semiconductor QDs grown by the melting-nucleation synthesis approach due to the relatively high temperature that was used in thermal annealing of samples.