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Design closure and parameter optimisation are crucial in creating cutting-edge antennas. Antenna performance can be improved by fine-tuning preliminary designs created using theoretical considerations and rough dimension adjustment via supervised parameter sweeps. This paper introduces a frequency reconfigurable antenna design that can operate at 28/38 GHz frequencies to meet FCC and Ofcom standards for 5G applications and in the 18 GHz frequency band for K-band radar applications. A PIN diode is used in this design to configure multiple frequency bands. The antenna has a modified rectangular patch-like structure and two optimised plugins on either side. The study that is being presented focuses on maximising the parameters that are subject to optimisation, including length (Ls), width (Ws), strip line width (W1), and height (ht), where the antenna characteristic parameters such as directivity is tuned by a hybrid optimisation scheme called Elephant Clan Updated Grey Wolf Algorithm (ECU-GWA). Here, the performance of gain and directivity are optimally attained by considering parameters such as length, width, ground plane length, width, height, and feed offsets X and Y. The bandwidth of the proposed antenna at − 10 dB is 0.8 GHz, 1.94 GHz, and 7.92 GHz, respectively, at frequencies 18.5 GHz, 28.1 GHz, and 38.1 GHz. Also, according to the simulation results, in the 18 GHz, 28 GHz, and 38 GHz frequencies S11, the return loss is − 60.81 dB, − 56.31 dB, and − 14.19 dB, respectively. The proposed frequency reconfigurable antenna simulation results achieve gains of 4.41 dBi, 6.33 dBi, and 7.70 dBi at 18.5 GHz, 28.1 GHz, and 38.1 GHz, respectively. Also, a microstrip quarter-wave monopole antenna with an ellipsoidal-shaped complementary split-ring resonator-electromagnetic bandgap structure (ECSRR-EBG) structure has been designed based on a genetic algorithm having resonating at 2.9 GHz, 4.7 GHz, 6 GHz for WLAN applications. The gain of the suggested ECSRR metamaterial and EBG periodic structure, with and without the ECCSRR bow-tie antenna. This is done both in the lab and with numbers. The measured result shows that the ECSRR metamaterial boosts gain by 5.2 dBi at 5.9 GHz. At 5.57 GHz, the two-element MIMO antenna achieves its lowest ECC of 0.00081. [ABSTRACT FROM AUTHOR]

We determined the properties of Zn1-xMgxSe semiconductor alloys through a combination of optical and photoelectron spectroscopy, x-ray diffraction, Rutherford backscattering spectrometry, and ab initio pseudopotential calculations. The complementary character of the techniques and the good agreement between calculated and experimental trends allowed us to explain some of the discrepancies between the reported properties of these wide band gap alloys. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The time dependent transition from hydrophobic to hydrophilic states of the metalorganic vapour phase epitaxy (MOVPE) grown InP, GaAs and InAs is systematically documented by contact angle measurements. Natural oxides forming on the surfaces of air-exposed materials, as well as the results of some typical wet chemical process to remove those oxides, were studied by X-ray photoemission spectroscopy (XPS), revealing, surprisingly, a fundamental lack of strong correlations between the surface oxide composition and the reported systematic changes in hydrophobicity. [ABSTRACT FROM AUTHOR]

Abstract: We present here the growth of GaAs, InAs and InGaAs nanowires by molecular beam epitaxy. The nanowires have been grown on different substrates [GaAs(001), GaAs(111), SiO2 and Si(111)] using gold as the growth catalyst. We show how the different substrates affect the results in terms of nanowire density and morphology. We also show that the growth temperature for the InGaAs nanowires has to be carefully chosen to obtain homogeneous alloys. [Copyright &y& Elsevier]

Background: Scabies or sarcoptic mange is an infestation of the skin caused by the mite Sarcoptes scabiei. Transmission from animals to humans occurs through close contact. The most common symptoms are papules, erythema, excoriations, hyperkeratosis, and hypotrichosis. In the province of Ferrara (Emilia Romagna, Italy) mange is endemic in wild animals, mostly in foxes, which can act as vectors for domestic animals and humans. Methods: From 2012 to 2020, 564 foxes were surveyed within the Wildlife Health Surveillance Regional Program, including microscopic examination in cases of skin lesions referable to scabies. In 2018, a domestic dog (10-year border collie, male), frequenting an uncultivated area colonized by foxes and located in the outskirts of Ferrara, showed scabby lesions mainly on the nose, around the eyes and on the back. Results: 11 out of 564 foxes resulted positive (1,95%), 6 cases out of 38 being in 2018 (15,8%). The parasite was detected by skin biopsy and direct microscopic examination in the domestic dog. The parasite was transmitted by the dog to the owner and the other two family members. Conclusions: The increased density of dogs and foxes in the Ferrara province, and the attitude of foxes to live near to human settlements, increase the risk of contacts between foxes, domestic animals and humans, even though stray dogs are uncommon. This case illustrates the interdependencies between animal health, human health and environment, a synergy that can enable exacerbation of diseases of zoonotic origin as highlighted by the One Health concept. It is therefore important to increase the investigation on paths as well as vectors of diseases and to find collaborative, multi-sectorial and transversal approaches to ensure quality health outcomes. The control of the disease requires an appropriate monitoring of dogs’ health being skin lesions in both, humans and animals, very similar to allergic dermatitis, which can delay the proper diagnosis of the disease. Key messages: • Sarcoptic mange is a zoonosis still present in Emilia Romagna, Italy. • The One Health approach is key to control the cycle of the zoonotic sarcoptic mange. [ABSTRACT FROM AUTHOR]

InGaAs/GaAs core-shell nanowires have been grown by molecular beam epitaxy. The core-shell nanowires show room temperature photoluminescence. At low temperatures their luminescence intensity is two to three orders of magnitudes larger than that of parent InGaAs nanowires grown without external GaAs shell. The nanowires have been structurally characterized by scanning electron microscopy and transmission electron microscopy. [ABSTRACT FROM AUTHOR]

We compare the In content of quaternary InxGa1-xAs1-yNy and ternary InxGa1-xAs layers grown by plasma-assisted molecular beam epitaxy in similar conditions. Indium incorporation is found to decrease monotonically with increasing nitrogen content. The magnitude of the reduction strongly depends on N concentration, reaching about 20% of the nominal In content for N concentrations of y=0.044. [ABSTRACT FROM AUTHOR]

We present experimental and theoretical studies of lattice-matched interfaces between Zn[sub 1-y]Mg[sub y]Se and Zn[sub 1-x]Cd[sub x]Se wide-band gap semiconductors. Ab initio pseudopotential calculations predict lattice matching for y/x∼1.6 and a valence band contribution to the band gap difference Q[sub v] decreasing gradually from 0.34 to 0.27 with increasing x and y. Experimental x-ray diffraction and photoemission spectroscopy results are mostly consistent with such predictions, although non-negligible deviations of the band offsets from commutativity were observed for selected alloy compositions. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The GaAs-like longitudinal-optical (LO) phonon frequency in hydrogenated GaAs1−xNx (x = 0.01) layers—with different H doses and similar low-energy irradiation conditions—was investigated by micro-Raman measurements in different scattering geometries and compared with those of epitaxial GaAs and as-grown GaAs1−xNx reference samples. A relaxation of the GaAs selection rules was observed, to be explained mainly on the basis of the biaxial strain affecting the layers. The evolution of the LO phonon frequency with increasing hydrogen dose was found to heavily depend on light polarization, thus suggesting that a linear relation between strain and the frequency of the GaAs-like LO phonon mode should be applied with some caution. Moreover, photoreflectance measurements in fully passivated samples of identical N concentration show that the blueshift of the GaAs-like LO frequency, characteristic of the hydrogenated structures, is dose-dependent and strictly related to the strain induced by the specific type of the dominant N-H complexes. A comparison of photoreflectance results with the finite element method calculations confirms that this dependence on the H dose is due to the gradual replacement of the N-2H complexes responsible for the electronic passivation of N with N-3H complexes, which are well known to induce an additional and sizeable lattice expansion. [ABSTRACT FROM AUTHOR]

ZnSe nanowires, 5–10  nm wide and several microns long, were fabricated by Au-catalyzed molecular beam epitaxy. Specially designed silicon–silicon dioxide substrates allowed an examination of individual nanowires with a combination of phase-contrast high-resolution transmission electron microscopy, Z-contrast scanning transmission electron microscopy imaging and energy-dispersive X-ray spectroscopy using a low-current electron probe with a diameter of 0.2  nm. Experimental results demonstrate direct evidence of Au incorporation within single-crystal sphalerite ZnSe nanowires. [ABSTRACT FROM AUTHOR]

ZnSe nanowires with a dominant wurtzite structure have been grown at low temperature (300 °C) by molecular beam epitaxy assisted by solid Au nanoparticles. The nanowires emission is polarized perpendicularly to their axis in agreement with the wurtzite selection rules. Alternations of wurtzite and zinc-blende regions have been observed by transmission electron microscopy, and their impact on the nanowires optical properties has been studied by microphotoluminescence. The nanowires show a dominant intense near-band-edge emission as well as the ZnSe wurtzite free exciton line. A type II band alignment between zinc-blende and wurtzite ZnSe is evidenced by time-resolved photoluminescence. From this measurement, we deduce values for the conduction and valence band offsets of 98 and 50 meV, respectively. [ABSTRACT FROM AUTHOR]

The GaAs-like longitudinal optical phonon frequency in two hydrogenated GaAs1-xNx/GaAs1-xNx:H microwire heterostructures-with similar N concentration, but different H dose and implantation conditions-has been investigated by micro-Raman mapping. In the case of GaAs0.991N0.009 wires embedded in barriers where GaAs-like properties are recovered through H irradiation, the phonon frequency in the barriers undergoes a blue shift with respect to the wires. In GaAs0.992N0.008 wires embedded in less hydrogenated barriers, the phonon frequency exhibits an opposite behavior (red shift). Strain, disorder, phonon localization effects induced by H-irradiation on the GaAs-like phonon frequency are discussed and related to different types of N-H complexes formed in the hydrogenated barriers. It is shown that the red (blue) character of the frequency shift is related to the dominant N-2H (N-3H) type of complexes. Moreover, for specific experimental conditions, an all-optical determination of the uniaxial strain field is obtained. This may improve the design of recently presented devices that exploit the correlation between uniaxial stress and the degree of polarization of photoluminescence. [ABSTRACT FROM AUTHOR]

The control of the doping in nanowires (NWs) is of fundamental importance for the implementation of NW-based devices. A method is presented to obtain local information about doping by monitoring the Fermi-energy position within the bandgap at the surface along single NWs through spatially resolved x-ray photoemission spectroscopy. The experimental results are complemented by theoretical simulations of the carrier profile, taking into account the presence of electronic surface states and quantifying the impact of carrier depletion at the NW surface. This combined approach allows to determine the effect of the incorporation of Si dopants in GaAs NWs following different growth protocols, such as vapor-liquid-solid axial growth or vapor-solid radial growth, and in the resulting core-shell structures and axial junctions. The method also revelaed the strong dependence of the resulting doping on the morphology of the single NW (orientation, shell thickness). This approach can be easily applied to other nanoscale objects, allowing the direct observation of how doping (or junctions, or adsorbates,...) may locally affect the position of the Fermi level at the surface, which is a crucial factor in several application fields, such as photovoltaic and photocatalysis. [ABSTRACT FROM AUTHOR]

Lattice-matched Zn[sub 0.85]Cd[sub 0.15]Se/Zn[sub 0.74]Mg[sub 0.26]Se multiple-quantum-well structures were obtained on GaAs(001) using graded-composition In[sub y]Ga[sub 1-y]As layers to match the II-VI lattice parameter to the III-V substrate. Cross-sectional transmission electron microscopy studies show that the effect of the crosshatch pattern of the In[sub y]Ga[sub 1-y]As surface is limited to long-period coherent undulations of quantum well and barrier layers. Optical measurements of the excitonic properties as a function of well thickness, complemented by self-consistent calculations of the transition energies, indicate good quantum confinement in the well, with a 68% conduction band contribution to the 0.482 eV band gap difference. [ABSTRACT FROM AUTHOR]

The effect of hydrogen irradiation on the optical properties of GaAs1-xNx/GaAs heterostructures was investigated using photoreflectance and reflectance techniques. Systematic measurements performed on both as-grown and hydrogenated samples for N-concentrations ranging from 0.0% to 3.5% and for H-implanted doses from 3 × 1018 to 6 × 1018 ions/cm2 have shown that (a) the H-induced widening of the energy gap is accompanied by a decrease of the refractive index of the H-treated samples with respect to the as-grown ones, resulting in an index mismatch that can be as large as 2% in the subgap spectral region; and (b) the presence of compressive strain in fully passivated GaAsN determines a decrease of the refractive index even below that of GaAs that can be eliminated via moderate thermal annealing. These findings are promising for the development of heterostructures with planar geometry, in which the simultaneous confinement of both carriers and photons, even on a nanometric scale, can be obtained in a single step process. [ABSTRACT FROM AUTHOR]

Self-catalyzed GaAs nanowire growth was obtained by molecular beam epitaxy on GaAs(001) substrates after predeposition of subnanometer-thick Si layers. Two substrate preparation methods are presented, the first based on the epitaxial growth of Si on GaAs and subsequent exposure to atmosphere, and the second on the direct deposition of Si on epiready GaAs substrates. X-ray photoemission spectroscopy shows that both methods result in a thin Si oxide layer that promotes the growth of GaAs nanowires aligned along the <111> direction. High densities of nanowires were obtained at substrate temperatures between 620 and 680 °C. Systematic electron microscopy studies indicate that nanowire growth is associated with the formation of Ga nanoparticles on the substrate surface, which act as a catalyst in the vapor-liquid-solid growth mechanism frame. The majority of the nanowires have a pure zinc-blende structure, and their photoluminescence is dominated by a photoluminescence peak 3 to 5 meV in width and centered at 1.516 to 1517 eV. [ABSTRACT FROM AUTHOR]

Micro-Raman spectroscopy is employed to study the phonon confinement in Au- and Mn-catalyzed GaAs and InAs nanowires. The phonon confinement model is used to fit the LO phonon peaks, which also takes into account the contribution to the asymmetry of the line shape due to the presence of surface optical (SO) phonons and structural defects. This also allows us to determine the correlation lengths in these wires, that is the average distance between defects and the defect density in these nanowires. Influence of these defects on the SO phonon is also investigated. A good agreement between the experimental results and the calculations for the SO phonon mode by using the dielectric continuum model is also obtained. [ABSTRACT FROM AUTHOR]

We report Raman studies of GaAs and InAs nanowires (NWs) grown on SiO2 and GaAs surfaces by means of catalyst-assisted molecular beam epitaxy. We have investigated several tens of NWs grown using either Mn or Au as a catalyst. The LO and TO phonon lines of the NWs showed an energy downshift and a broadening as compared to the lines usually observed in the corresponding bulk materials. A doublet is sometimes observed in the LO region due to the observation of a signal attributed to the surface optical (SO) phonon. The energy position of the SO phonon agrees with the values expected considering the section diameter of the NWs. LO and TO downshifts are due to the presence of structural defects within the NWs. The larger the energy downshift, the smaller the dimension of the defect-free regions. The results demonstrate that different catalysts provide wires with comparable crystal quality. The measurements also point out that differences in defect density can be found in wires coming from the same batch indicating that a substantial effort will be needed to obtain high homogeneities of the NW quality. [ABSTRACT FROM AUTHOR]

Presents information on the fabrication of the lattice-matched ZnSe/InxGa1-xAs heterostructures. Circumstances surrounding the compensation of the partial character of the strain relaxation within the ternary layer; What the complex surface morphology reflects; Information on the results.

We report on a novel lithographic approach for the fabrication of integrated quantum dot (QD)-photonic crystal (PhC) nanocavity systems. We exploit unique hydrogen's ability to tailor the band gap energy of dilute nitride semiconductors to fabricate isolated site-controlled QDs via a spatially selective hydrogenation at the nanometer-scale. A deterministic integration of the realized site-controlled QDs with PhC nanocavities is provided by the inherent realignment precision (~ 20 nm) of the electron beam lithography system used for the fabrication of both QDs and PhC cavities. A detailed description of the fabrication steps leading to the realization of integrated QD-PhC cavity systems is provided, together with the experimental evidence of a weak coupling effect between the single-photon emitter and the PhC cavity. [ABSTRACT FROM AUTHOR]

Heat management mechanisms play a pivotal role in driving the design of nanowire (NW)-based devices. In particular, the rate at which charge carriers cool down after an external excitation is crucial for the efficiency of solar cells, lasers, and high-speed transistors. Here, we investigate the thermalization properties of photogenerated carriers by continuous-wave (cw) photoluminescence (PL) in InP and GaAs NWs. A quantitative analysis of the PL spectra recorded up to 310 K shows that carriers can thermalize at a temperature much higher than that of the lattice. We find that the mismatch between carrier and lattice temperature, ΔT, increases exponentially with lattice temperature and depends inversely on the NW diameter. ΔT is instead independent of other NW characteristics, such as crystal structure (wurtzite vs zincblende), chemical composition (InP vs GaAs), shape (tapered vs columnar NWs), and growth method (vapor-liquid-solid vs selective-area growth). Remarkably, carrier temperatures as high as 500 K are reached at the lattice temperature of 310 K in NWs with ~70 nm diameter. While a population of nonequilibrium carriers, usually referred to as "hot carriers", is routinely generated by high-power laser pulses and detected by ultrafast spectroscopy, it is quite remarkable that it can be observed in cw PL measurements, when a steady-state population of carriers is established. Time-resolved PL measurements show that even in the thinnest NWs carriers have enough time (~1 ns) after photoexcitation to interact with phonons and thus to release their excess energy. Nevertheless, the inability of carriers to reach a full thermal equilibrium with the lattice points to inhibited phonon emission primarily caused by the large surface-to-volume ratio of small diameter NWs. [ABSTRACT FROM AUTHOR]

GaAsN/GaAsN:H heterostructures were made by an in-plane selective hydrogen incorporation controlled by H-opaque metallic masks. The strain field and hydrogen distributions in GaAsN micro-sized wires thus obtained have been mapped by an all optical procedure that combines micro-Raman scattering and photoreflectance spectroscopy. The strain field is related to the formation of N-H complexes along the hydrogen diffusion profile with an ensuing expansion of the GaAsN lattice whose patterning generates an anisotropic stress in the sample growth plane. These results highlight a powerful non-invasive tool to simultaneously determine both the H diffusion profile and the related strain field distribution. [ABSTRACT FROM AUTHOR]

We show that the dissociation of the N-H complex in hydrogenated III-N-Vs can be laser activated at temperatures that are significantly smaller than those (\>200°C) required for thermal dissociation due to a resonant photon absorption by the N-H complex. This phenomenon provides a mechanism for profiling the band-gap energy in the growth plane of the III-N-Vs with submicron spatial resolution and high energy accuracy; the profiles are erasable and the alloys can be rehydrogenated making any nanoscale in-plane band-gap profile rewritable. [ABSTRACT FROM AUTHOR]

Hydrogen incorporation in diluted nitride semiconductors dramatically modifies the electronic and structural properties of the crystal through the creation of nitrogen-hydrogen complexes. We report a convergent beam electron-diffraction characterization of diluted nitride semiconductor-heterostructures patterned at a sub-micron scale and selectively exposed to hydrogen. We present a method to determine separately perpendicular mismatch and static disorder in pristine and hydrogenated heterostructures. The roles of chemical composition and strain on static disorder have been separately assessed. [ABSTRACT FROM AUTHOR]

The electrical properties of untreated and hydrogen-irradiated GaAs1-xNx are investigated by conductive-probe atomic force microscopy (CP-AFM). After hydrogen irradiation, the resistance R of GaAs1-xNx increases by more than three orders of magnitude while that of a N-free GaAs reference slightly decreases. Thermal annealing at 550°C of H-irradiated GaAs1-xNx restores the pristine electrical properties of the as-grown sample thus demonstrating that this phenomenon is fully reversible. These effects are attributed to the nitrogen-hydrogen complexes that passivate N in GaAs1-xNx (thus restoring the energy gap of N-free GaAs) and, moreover, reduce the carrier scattering time by more than one order of magnitude. This opens up a route to the fabrication of planar conductive/resistive/conductive heterostructures with submicrometer spatial resolution, which is also reported here. [ABSTRACT FROM AUTHOR]

Abstract: A dedicated specimen holder has been designed to perform low-voltage scanning transmission electron microscopy in dark field mode. Different test samples, namely InGaAs/GaAs quantum wells, InGaAs nanowires and thick InGaAs layers, have been analysed to test the reliability of the model based on the proportionality to the specimen mass-thickness, generally used for image intensity interpretation of scattering contrast processes. We found that size of the probe, absorption and channelling must be taken into account to give a quantitative interpretation of image intensity. We develop a simple procedure to evaluate the probe-size effect and to obtain a quantitative indication of the absorption coefficient. Possible artefacts induced by channelling are pointed out. With the developed procedure, the low voltage approach can be successfully applied for quantitative compositional analysis. The method is then applied to the estimation of the In content in the core of InGaAs/GaAs core-shell nanowires. [Copyright &y& Elsevier]

In this work it is demonstrated how in situ high-resolution X-ray diffraction (HRXRD), performed during thermal annealing and employing a conventional laboratory source, can be used to obtain information on the evolution kinetics of very small complexes formed in an epitaxial layer. HRXRD allows the measurement of changes in the lattice parameter of the layer (i.e. the layer strain) with different annealing strategies (by linear temperature ramp or isothermal annealing). On the basis of these data and using an appropriate model, the dissolution energy values of the complexes can be extracted. The underlying idea is that every type of complex present in the layer gives a specific lattice strain which varies under annealing, allowing their evolution to be traced accurately. As an example, this methodology is applied to the study of N-H complexes formed in hydrogen-irradiated GaAs1 -~N~/GaAs layers. [ABSTRACT FROM AUTHOR]

Abstract: We report on structural and electrical properties of GaAs nanowires (NWs) grown by molecular beam epitaxy (MBE) on GaAs and SiO2 substrates using Au as growth catalyst. Au–Ga particles are observed on the top of the NWs by transmission electron microscopy (TEM). In most of the observed cases, individual particles contain two Au–Ga compositions, in particular orthorhombic AuGa and β′ hexagonal Au7Ga2. The wires grown on GaAs are regularly shaped and tidily oriented on both (100) and (111)B substrates. TEM also reveals that the NWs have a wurtzite lattice structure. Electrical transport measurements indicate that nominally undoped NWs are weakly n-type while both Be- and Si-doped wires show p-type behaviour. The effect of the lattice structure on impurity incorporation is briefly discussed. [Copyright &y& Elsevier]

A natural application of the emerging technique of photoemission microscopy to the study of semiconductor interfaces involves measuring a device in cross section to directly determine heterojunction parameters. We present here results on p-n GaAs homojunctions, which served as a prototype system to demonstrate the applicability of this technique to buried semiconductor interfaces. We also describe preliminary measurements of the electrostatic potential profile across Al/GaAs Schottky junctions. [ABSTRACT FROM AUTHOR]

Lattice-matched n-n ZnSe/In[sub 0.04]Ga[sub 0.96]As heterojunctions were studied by means of current density versus voltage (J–V) and capacitance versus voltage (C–V) measurements. The resulting characteristics indicate that the behavior of this n-n heterostructure can be explained by a back-to-back double Schottky diode model. The value of conduction band discontinuity (ΔE[sub c]) is found to be 0.10–0.12 eV. © 1998 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We use a focussed laser beam to control the electronic activity of N- and H-atoms in a dilute nitride Ga(AsN)/GaAs quantum well. Our approach yields submicron resolution in the spatial manipulation of the electronic properties and can provide an alternative method to masking techniques for H-defect engineering and in-plane patterning of the band gap energy. [ABSTRACT FROM AUTHOR]

The expansion of the GaAsN lattice following hydrogen incorporation is spatially patterned so as to generate an anisotropic stress in the sample growth plane. The resulting in-plane symmetry breaking determines an in-plane polarization dependence of the light emitted along the crystal growth direction in agreement with optical selection rules and strain field calculations. [ABSTRACT FROM AUTHOR]

The influence of temperature on deuterium (or hydrogen) diffusion in GaAsN is investigated by secondary ion mass spectrometry and photoluminescence (PL). Deuterium incorporation at 200 °C leads to an extremely sharp D concentration profile, which decreases by a factor of 10 within 5 nm. This has great relevance to the attainment of an in-plane band gap engineering of dilute nitrides as demonstrated by PL in ensembles of artificial GaAsN wires. [ABSTRACT FROM AUTHOR]

The effect of deuterium irradiation on the optical and strain properties of GaAsN/GaAs heterostructures was investigated by photoreflectance and reflectance techniques. The strain occurring in as-grown and deuterated GaAsN layers is monitored and measured by means of photoreflectance spectroscopy, highlighting the strain inversion after irradiation. By combining static and modulated reflectance results, evidence is given that the deuterium-induced recovery of the GaAs band gap as well as the strain inversion in GaAsN layers are accompanied by a 0.4%–0.8% reduction of the refractive index in the 1.31 and 1.55 μm spectral windows of interest for fiber optic communications. These results anticipate a single step process to an in-plane confinement of carriers and photons. [ABSTRACT FROM AUTHOR]

Hydrogenation of GaAs1-xNx and GaP1-xNx epilayers grown on GaAs(001) and GaP(001) surfaces, respectively, is known to passivate the electronic activity of nitrogen through the formation of specific nitrogen-hydrogen complexes. The same epilayers also undergo a strain reversal from tensile (as grown) to compressive (fully hydrogenated). The authors show that the extent of strain reversal is determined exclusively by the nitrogen concentration. By performing in situ high resolution x-ray diffraction measurements during annealing and photoluminescence studies, the authors demonstrate that the lattice properties of fully hydrogenated GaAs1-xNx are ruled by a H complex, which is different and less stable than that responsible for electronic passivation of nitrogen in GaAs1-xNx. [ABSTRACT FROM AUTHOR]

We compare the luminescence from InAsN/GaAs and InAsN/GaAsN quantum dots with that obtained from InGaNAsN/GaAs quantum wells grown in the same experimental system. All structures were engineered to emit near 1.3 μm at room temperature. Quantum-dot emitters were found to exhibit higher thermal stability and did not require postgrowth annealing. The use of GaAsN barriers as opposed to GaAs barriers provided for narrower and more intense quantum-dot luminescence. [ABSTRACT FROM AUTHOR]

Single-crystal ZnSe nanowires are grown on a prepatterned gold catalyst by molecular-beam epitaxy. Optimum selectivity and maximum nanowire densities are obtained for growth temperatures in the range 400–450 °C, but gold-assisted growth is demonstrated for temperatures as low as 300 °C. This suggests a diffusion process on/through the catalyst particle in the solid state, in contrast to the commonly assumed liquid phase growth models. Straight wires, as thin as 10 nm, nucleate together with thicker and saw-like structures. A gold particle is always found at the tip in both cases. [ABSTRACT FROM AUTHOR]

The silicon concentration profile in Si–GaAs (001) superlattices grown by molecular beam epitaxy was investigated using scanning transmission electron microscopy high-angle annular dark-field (HAADF) imaging. Comparison with atomic resolution results obtained through cross-sectional scanning tunneling microscopy indicates that, by choosing appropriate experimental conditions, HAADF imaging can be used to gauge the Si distribution in GaAs on the atomic scale even without any image simulation. [ABSTRACT FROM AUTHOR]

Using a combination of scanning tunneling microscopy and spectroscopy techniques, and a series of periodic δ-doped structures in GaAs, we show that the electrostatic potential can be mapped along {110} cross sections in semiconductor nanostructures with nanometer resolution and 30 meV sensitivity. Our results also indicate that microscopic capacitors with plates spaced by as little as 2 nm can be implemented by δ doping for band gap engineering purposes. [ABSTRACT FROM AUTHOR]

To probe the development of Si-GaAs superlattices, we performed Si K-edge x-ray absorption measurements on periodic Si δ-doped structures in GaAs, for equivalent Si thicknesses of 0.02, 0.2, 0.5, 1, 2, and 4 monolayers (ML). We detected the presence of both Si-Si and Si-As (or Si-Ga) bonds and followed the variation of the coordination numbers as a function of the equivalent thickness of the Si layers. The Si-Si coordination number was found to gradually increase with increasing thickness, but Si-Si bonds were always detected, even at equivalent Si coverages of 0.02 ML. This indicates that the preferred growth conditions for Si-GaAs superlattices lead to widespread Si clustering and self-compensation, and suggests that lateral growth of such clusters to achieve coalescence may be the main mechanism for Si quantum well development. [ABSTRACT FROM AUTHOR]

An important application of photoemission spectromicroscopy would be to measure heterostructures and semiconductor devices in cross section to directly determine band offsets and band bending. We present here studies of p-n GaAs homojunctions and Al/GaAs Schottky junctions fabricated by molecular-beam epitaxy. Our results suggest that a minimum experimental uncertainty of about 0.15 eV will effect band offset determination. In general, useful quantitative information on the junction electrostatics can be obtained provided that the experimental data are analyzed to substract the diffuse photon background and take into account the intensity profile of the photon spot. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]