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We studied the photoluminescence (PL) properties of In0.2Ga0.8As/GaAs quantum well structures grown by molecular beam epitaxy on (311)-oriented substrates. The structure consists of three quantum wells (QWs) of 100, 50, and 25 Å nominal thickness. The temperature dependence of the PL emission from the QWs in the range of 5–250 K is reported. Three models by Varshni, Viña, and Pässler, respectively, were employed to analyze the variation in the excitonic energy transitions as a function of temperature. We compared the excitonic behavior with the band gap temperature dependence of bulk In0.2Ga0.8As and found a difference, as opposed to the unstrained AlGaAs/GaAs system. We attributed this difference to the modification of the QW energy levels by the quantum confinement Stark effect, which is temperature and well width dependent. [ABSTRACT FROM AUTHOR]

This work studies the Si-doping of GaAs on (631)-oriented substrates as a function of the As4-beam equivalent pressure (PAs). The electrical properties obtained by Hall effect measurements show that the mobility of the layers grown on (631)-substrates present changes related to carrier compensation processes and the Si-doping changes from p- to n-type when PAs is increased. The optical properties of the samples, as observed by photoluminescence (PL) spectroscopy, modified according to the electrical characteristics. For (631)-samples, when PAs is increased the energy of the maximum intensity PL peak redshifts in the p-type region but, after the threshold of the conduction type conversion, the peak blueshifts in the n-type region. The variation of the PL excitation intensity also shifts the emission energy of the samples as a consequence of the increasing recombination rate for close pairs in donor acceptor pair recombination. Photoluminescence as a function of temperature shows that the activation energy of the PL lines transition is enhanced as PAs is increased. [ABSTRACT FROM AUTHOR]

Quantum well (QW) structures of Al x Ga1- x As/GaAs with x = 0.3 were characterized by photoluminescence spectroscopy (PL) with circularly polarized excitation at a temperature of 1.6 K. The samples contained three QWs with thickness of 7, 5, and 3 nm grown by molecular beam epitaxy (MBE) on a 500 nm thick buffer layer. Four samples with identical geometry but different surface treatments (in-situ etching the GaAs buffer with Cl2 at different temperatures, and air-exposed buffer, respectively) were compared. The degree of circular polarization of the PL and its decrease in a magnetic field applied perpendicularly to the direction of propagation of light (Hanle effect) allows the determination of the interband lifetime τ and the spin lifetime τ s of the electrons. These lifetimes were different in the different QWs and strongly depend on the growth procedure. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Metallomicelles of Ru(II) showed cytotoxic activity and selectivity by some cancer cell lines. • Confocal fluorescence microscopy demonstrated the interaction between micelles and DNA. • Metallomicelles of Ru(II) showed a good internalization into cancer and normal cells at low surfactant concentrations. • DNA acted as a catalyst in the structural change from spherical to elongated micelles. Abstract The use of nanovectors in several medicinal treatments has reached a great importance in the last decade. Some drugs need to be protected to increase their lifetimes in the blood flow, to avoid degradation, to be delivered into target cells or to decrease their side effects. The goal of this work was to design and prepare nanovectors formed by novel surfactants derived from the [Ru(bpy) 3 ]2+ complex. These amphiphilic molecules are assembled to form metallomicelles which can act as pharmaceutical agents and, at the same time, as nanovectors for several drugs. TEM images showed a structural transition from spherical to elongated micelles when the surfactant concentration increased. Fluorescence microscopy confirmed the internalization of these metallomicelles into diverse cell lines and cytotoxicity assays demonstrated specificity for some human cancer cells. The encapsulation of various antibiotics was carried out as well as a thorough study about the DNA condensation by the metallomicelles. To the best of our knowledge, applications of these metallomicelles have not been shown in the literature yet. [ABSTRACT FROM AUTHOR]

The authors report the photoluminescence and photoreflectance characteristics of molecular beam epitaxy grown InAs nanostructures on GaAs (631)-oriented substrates. Prior to the InAs growth, self-assembled nanochannels on the GaAs buffer layer were formed, which later were used as templates for nanostructures formation. Different samples were prepared by varying the amount of InAs from 0.75 to 2 ML (monolayer), 50 nm of GaAs was grown on top as a capping layer. Low temperature photoluminescence spectroscopy showed intense optical transitions in the spectra, their energy position directly depends on the quantity of InAs deposited. The self-assembling of InAs quantum wires (QWRs) at the early stages of growth is suggested. Anisotropy effects in the InAs nanostructures were corroborated by polarized photoluminescence supporting the proposal of formation of QWRs. Photoreflectance spectroscopy at room temperature was also employed to characterize the samples. It is found that in addition to the band-gap energy transition, features associated with quantum confinement in the wetting layer were observed even for very low quantities of InAs deposited. [ABSTRACT FROM AUTHOR]

Abstract: GaN thin films grown by MOCVD on (0001) Al2O3 substrates at different growth pressures were characterized by field-emission scanning electron microscopy, atomic force microscopy, micro-Raman, and photoluminescence at room temperature. It was found that there is an optimum pressure of 76Torr at which the structural and optical properties of the GaN samples are superior. On the other hand samples grown at higher pressure exhibited hexagonal surface pits and surface spirals. The results showed that the growth pressure strongly influences the morphology, and significantly affects the structural and optical properties of the GaN epilayers. [Copyright &y& Elsevier]

Abstract: A series of quantum well (QW) structures of Al0.3Ga0.7As/GaAs were characterized by photoluminescence spectroscopy with circularly polarized excitation at 1.6 K. The samples were grown by molecular beam epitaxy on a 500 nm thick GaAs buffer layer and contained three QW structures with thicknesses of 7, 5, and 3 nm, respectively. Four samples were prepared with different processing of the GaAs buffer layer surface (i: continuous growth, ii: in situ etching the GaAs buffer with Cl2 at 70 °C, iii: at 200 °C, respectively and iv: air-exposed buffer). The influence of buffer surface preparation on sample characteristics was analyzed. Using the Hanle effect the interband lifetime and the spin lifetime of the electrons were determined. A negative spin polarization was observed if the photon energy of the exciting light exceeds the difference between the spin–orbit band and the conduction band. This inverse circular polarization could be related to the quality of the sample. [ABSTRACT FROM AUTHOR]

Abstract: GaAs (100) substrates prepared in a quartz chamber under a H2/As4 flux, and then exposed to air were used for the subsequent growth of GaAs–AlGaAs single quantum wells by molecular beam epitaxy. The substrates prepared by this method showed atomically flat surfaces corroborated by atomic force microscopy analysis. Quantum wells grown directly on these substrates without a GaAs buffer layer exhibited narrow and intense photoluminescence peaks, an indication of a high quality material. The secondary ion mass spectroscopy analysis showed oxygen and carbon traces on the first AlGaAs barrier layer grown after air exposure with no effects on the quantum wells optical emissions. From the results we conclude that the prepared GaAs surfaces are useful for the epitaxial growth of high quality quantum structures. [Copyright &y& Elsevier]

In+ ion implantation was performed into a GaN epi-layer with dose and energy of 5 × 10 15 cm −2 and 25 keV respectively. After implantation, a thermal annealing process was employed and then the characterization was carried out by HRXRD, Raman spectroscopy, STEM, SIMS, XPS, and Photoluminescence. The maximum Indium concentration was measured by SIMS reaching to an atomic concentration of 3%. The HRXRD revealed the formation of In x Ga 1-x N with a variable distribution of Indium due to the implantation profile. The nucleation of In x Ga 1-x N was confirmed by the observation of interplanar spacings of 0.267 nm. The Photoluminescence analysis showed a modification of GaN spectra as a function of annealing temperature with an interesting green emission for samples annealed at 500 °C. The green emission is explained by the formation of In x Ga 1-x N with x value as high as 0.32 within rich Indium regions. [ABSTRACT FROM AUTHOR]

In this work, we report on self-assembling of In x Ga 1-x N nanostructures under strong nitrogen-rich conditions on Si (111) substrates by molecular beam epitaxy. In-situ analysis of the reflection high-energy electron diffraction patterns allowed to follow the strain evolution of the films as well as to monitor the morphological changes related to the In incorporation. Scanning electron microscopy and atomic force microscopy images of the samples evidenced the growth of different nanostructures such as nanocolumns and nanowalls depending on the In content. X-ray diffraction (XRD) measurements allowed to determine the indium concentration while Rutherford backscattering spectrometry (RBS) was used to obtain the composition and thickness of the films and to explore the way in which In and Ga atoms are incorporated in the In x Ga 1-x N ternary alloy. XRD and RBS complementary analysis suggests that phase separation, occurring at the higher indium concentration, induces both the In and Ga rich phases segregation towards the external surface of the growths. Therefore, the columnar surface arrangement observed on the extreme binary compounds is transformed into separated nanowalls as the indium content increases. The probable origin of this morphology change is discussed. A shift towards lower energies of the low temperature photoluminescence spectra was observed for increased In concentration and a value of the bowing band gap parameter of about 3 was estimated using the extrema binary compounds and the intermediated indium concentration samples. [ABSTRACT FROM AUTHOR]

In the present work, we report on molecular beam epitaxy growth of Mn-doped GaAs films at the relatively high temperature (HT) of 530 °C. We found that by increasing the Mn atomic percent, Mn%, from 0.01 to 0.2, the surface morphology of the samples is strongly influenced and changes from planar to corrugated for Mn% values from 0.01 to 0.05, corresponding to nanostructures on the surface with dimensions of 200–300 nm and with the shape of leave, to nanowire-like structures for Mn% values above 0.05. From reflection high-energy electron diffraction patterns, we observed the growth mode transition from two- to three-dimensional occurring at a Mn% exceeding 0.05. The optical and electrical properties were obtained from photoluminescence (PL) and Hall effect measurements, respectively. For the higher Mn concentration, besides the Mn related transitions at approximately 1.41 eV, PL spectra sharp peaks are present between 1.43 and 1.49 eV, which we related to the coexistence of zinc blende and wurtzite phases in the nanowire-like structures of this sample. At Mn% of 0.04, an increase of the carrier mobility up to a value of 1.1 × 10 3 cm 2 /Vs at 77 K was found, then decreases as Mn% is further increased due to the strengthening of the ionized impurity scattering. [ABSTRACT FROM AUTHOR]

Abstract: GaN synthesized by close space vapor transport in vacuum using GaN powder as the source material is reported. According to X-ray diffraction measurements, samples grown onto sapphire substrates are polycrystalline with the wurzite structure, while those grown onto fused silica substrates are amorphous. Scanning electron microscope and energy dispersive spectroscopy results show that the surface of the samples is composed of rounded droplets of GaN. Room temperature photoluminescence shows near band-edge emission and a broad defect band. Possible mechanisms allowing the deposition of GaN from the vapors of GaN powder are discussed. [Copyright &y& Elsevier]

Abstract: In this work the incorporation of oxygen in Al0.2Ga0.3In0.5P:Be layers lattice-matched to GaAs grown by solid source molecular beam epitaxy (SSMBE) was studied by secondary ion mass spectrometry (SIMS) and photoluminescence (PL) spectroscopy. By increasing the temperature of the phosphorous cracking zone from 800 to 1000°C the amount of oxygen was considerably raised by more than one order of magnitude as measured by SIMS. The increasing oxygen content resulted in the creation of radiative deep-defects in the samples, some of them identified as transitions between O-related moderately deep donor-like states and Be-acceptor levels (DdAP) as observed by low-temperature PL spectroscopy. Other observed lines were associated with Be-acceptor levels (A0,X), shallow impurities (A,X) and the band-to-band transition (B,B). On the other hand, as the beryllium concentration increased the PL intensity of the A0,X and DdAP lines increased, indicating that Be-incorporation in the Al0.2Ga0.3In0.5P epilayers enhances the probability that A0,X and DdAP transitions occur. After annealing the samples, the DdAP transition significantly increased due to further activation of O-related moderately deep donor-like states. Also the 15K-PL spectra from annealed samples showed another lower-energy broad band located at 0.271eV below the AlGaInP band edge, presumably related with oxygen deep-defect levels (O,DL). [Copyright &y& Elsevier]

Abstract: Quantum well (QW) structures of Al x Ga1–x As/GaAs were characterized by photoluminescence technique as a function of the temperature between 10 and 300 K. The structures were grown on a 500 nm thick GaAs buffer layer with Molecular Beam Epitaxy technique. We have studied the properties of in-situ Cl2-etched GaAs surfaces and overgrown QW structures as a function of the etching temperature (70 and 200 °C). Several models were used to fit the experimental points. Best fit to experimental points was obtained with the Pässler model. [Copyright &y& Elsevier]

Abstract: In this work, we have studied the dependence of the size and luminescence of self-assembled InAs quantum dots (SAQDs) on the growth conditions. The SAQDs were grown on GaAs (100) substrates by molecular beam epitaxy (MBE). Their structural and optical properties were studied by atomic force microscopy (AFM), and photoluminescence spectroscopy (PL). The growth of the InAs SAQDs was in situ monitored by reflection high-energy electron diffraction (RHEED). The shape and size of the InAs SAQDs were significantly affected by the growth temperature and the arsenic over-pressure. We observe a decrease of the SAQDS density and an increase in their height by increasing the growth temperature, and/or decreasing the arsenic over-pressure. This is accompanied by a remarkable red-shift of the PL emission energy from 1.3 to . [Copyright &y& Elsevier]

Abstract: InAs layers with thickness of monolayer (-layers) were grown by MBE embedded in GaAs barriers in the direction [100]. Photoluminescence (PL) spectroscopy was employed to study the electronic transitions in the -layers. By secondary-ion mass spectroscopy (SIMS) we checked out the possible In segregation. The samples consist of five InAs -layers embedded in between 60nm-thick GaAs barriers, such that the electron wave functions do not overlap each other, as we verified with a model of a square quantum well (SQW), which help us to calculate also the well width. [Copyright &y& Elsevier]