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The internal loss at the lasing threshold were studied experimentally and numerically in laser cavities comprising dense arrays of InGaAs/GaAs quantum dots (quantum well-dots) as a function of the number of their planes and the output loss. Numerical values of the parameters were found that determine the free-carrier absorption in the active region and in the waveguiding layer. The optimal design of the laser diode was determined to achieve the highest external differential efficiency. [ABSTRACT FROM AUTHOR]

In this paper, the optical properties of two-dimensional coupled concentric double quantum rings with a parabolic confinement potential are studied theoretically. The optical absorption coefficient for the transition from the ground state to the first excited state is calculated. The effects of inter-ring coupling, internal or external ring width variation, and on-center donor and acceptor impurities are investigated. The peak value of the absorption coefficient decreases when the width of the internal ring is decreased, but reducing the width of the external ring causes the absorption coefficient to first increase and then decrease. In addition, concentric double quantum rings with a wider internal (external) ring absorb the photons with higher (lower) energies. An increment of the inter-ring coupling causes the concentric double quantum rings to absorb photons with higher energies. Although the on-center impurity reduces the magnitude of the absorption coefficient, the decrement is considerable for the donor impurity rather than the acceptor impurity. It is shown that the peak value position of the absorption coefficient has an obvious blue-shift (red-shift) in the presence of donor (acceptor) impurity. [ABSTRACT FROM AUTHOR]

Controlling the morphology and composition of semiconductor nano- and micro-structures is crucial for fundamental studies and applications. Here, Si-Ge semiconductor nanostructures were fabricated using photolithographically defined micro-crucibles on Si substrates. Interestingly, the nanostructure morphology and composition of these structures are strongly dependent on the size of the liquid–vapour interface (i.e., the opening of the micro-crucible) in the CVD deposition step of Ge. In particular, Ge crystallites nucleate in micro-crucibles with larger opening sizes (3.74–4.73 μm2), while no such crystallites are found in micro-crucibles with smaller openings of 1.15 μm2. This interface area tuning also results in the formation of unique semiconductor nanostructures: lateral nano-trees (for smaller openings) and nano-rods (for larger openings). Further TEM imaging reveals that these nanostructures have an epitaxial relationship with the underlying Si substrate. This geometrical dependence on the micro-scale vapour–liquid–solid (VLS) nucleation and growth is explained within a dedicated model, where the incubation time for the VLS Ge nucleation is inversely proportional to the opening size. The geometric effect on the VLS nucleation can be used for the fine tuning of the morphology and composition of different lateral nano- and micro-structures by simply changing the area of the liquid–vapour interface. [ABSTRACT FROM AUTHOR]

We studied the influence of the arsenic pressure during low-temperature GaAs overgrowth of InAs quantum dots on their optical properties. In the photoluminescence spectrum of quantum dots overgrown at a high arsenic pressure, we observed a single broad line corresponding to unimodal size distribution of quantum dots. Meanwhile, two distinct peaks (~1080 and ~1150 nm) at larger wavelengths are found in the spectra of samples with quantum dots overgrown at a low arsenic pressure. We attributed this phenomenon to the high-pressure suppression of atom diffusion between InAs islands at the overgrowth stage, which makes it possible to preserve the initial unimodal size distribution of quantum dots. The same overgrowth of quantum dots at the low arsenic pressure induces intensive mass transfer, which leads to the formation of arrays of quantum dots with larger sizes. Integrated photoluminescence intensity at 300 K is found to be lower for quantum dots overgrown at the higher arsenic pressure. However, a difference in the photoluminescence intensity for the high- and low-pressure overgrowths is not so significant for a temperature of 77 K. This indicates that excess arsenic incorporates into the capping layer at high arsenic pressures and creates numerous nonradiative recombination centers, diminishing the photoluminescence intensity. [ABSTRACT FROM AUTHOR]

Since the emergence of one-dimensional nanostructures, in particular the bandgap-graded semiconductor nanowires/ribbons or heterostructures, lots of attentions have been devoted to unraveling their intriguing properties and finding applications for future developments in optical communications and integrated optoelectronic devices. In particular, the ability to modulate the bandgap along a single nanostructure greatly enhances their functionalities in optoelectronics, and hence these studies are essential to pave the way for future high-integrated devices and circuits. Herein, we focus on a brief review on recent advances about the synthesis through a magnetic-pulled chemical vapor deposition approach, crystal structure and the unique optical and electronic properties of on-nanostructures semiconductors, including axial nanowire heterostructures, asymmetrical/symmetric bandgap gradient nanowires, lateral heterostructure nanoribbons, lateral bandgap graded ribbons. Moreover, recent developments in applications using low-dimensional bandgap modulated structures, especially in bandgap-graded nanowires and heterostructures, are summarized, including multicolor lasers, waveguides, white-light sources, photodetectors, and spectrometers, where the main strategies and unique features are addressed. Finally, future outlook and perspectives for the current challenges and the future opportunities of one-dimensional nanostructures with bandgap engineering are discussed to provide a roadmap future development in the field. [ABSTRACT FROM AUTHOR]

Controlling the morphology and composition of semiconductor nano- and micro-structures is crucial for fundamental studies and applications. Here, Si-Ge semiconductor nanostructures were fabricated using photolithographically defined micro-crucibles on Si substrates. Interestingly, the nanostructure morphology and composition of these structures are strongly dependent on the size of the liquid–vapour interface (i.e., the opening of the micro-crucible) in the CVD deposition step of Ge. In particular, Ge crystallites nucleate in micro-crucibles with larger opening sizes (3.74–4.73 μm2), while no such crystallites are found in micro-crucibles with smaller openings of 1.15 μm2. This interface area tuning also results in the formation of unique semiconductor nanostructures: lateral nano-trees (for smaller openings) and nano-rods (for larger openings). Further TEM imaging reveals that these nanostructures have an epitaxial relationship with the underlying Si substrate. This geometrical dependence on the micro-scale vapour–liquid–solid (VLS) nucleation and growth is explained within a dedicated model, where the incubation time for the VLS Ge nucleation is inversely proportional to the opening size. The geometric effect on the VLS nucleation can be used for the fine tuning of the morphology and composition of different lateral nano- and micro-structures by simply changing the area of the liquid–vapour interface.

Modal absorptions in laser-like heterostructures containing InAs self-assembled quantum dots (QDs) and InGaAs quantum well-dots (QWDs) have been studied. The evaluation of photoresponse as a function of waveguide length has allowed us to determine per-layer modal absorptions of 69 and 13 cm-1 for the ground state optical transitions of QWDs and QDs, respectively. The values of the modal absorption can be used as a measure of the maximal (saturated) modal gain. To compare quantum heterostructures with different dimensionality we have introduced the layer gain constant, a parameter characterizing the light transmittance through the absorbing or gaining layer. We have shown that the QWD layer gain constant significantly exceeds quantum well and quantum dot ones. [ABSTRACT FROM AUTHOR]

Freestanding semiconductor nanowires have opened up possibilities for semiconductor devices, enabling geometries, material combinations, and strain states, which were not previously possible. Along these lines, spontaneous bending in asymmetric core–shell nanowire heterostructures has recently been proposed as a means to realize previously unimagined device geometries, strain-gradient engineering, and bottom-up device fabrication. The synthesis of these nanostructures makes use of the nanowire geometry and the directionality of the shell deposition process. Here, we explore the underlying mechanisms of this bending process by following the evolution of nanowires during asymmetric shell deposition. We show how bending can lead to dramatic local shell thickness, curvature, and strain variations along the length of the nanowire, and we elucidate the dependence of shell growth and bending on parameters such as the core and shell dimensions and materials and angle of incidence of the deposition source. In addition, deposition shadowing by neighboring nanowires is explored and employed to connect nanowire pairs, which could be used to fabricate nanowire sensors. GaAs–InP and GaAs–(Al,In)As core–shell nanowire growth experiments are compared to model results. These findings will guide future experiments and help pave the way to bent nanowire devices. [ABSTRACT FROM AUTHOR]

We theoretically investigate the dwell time for electrons in an antiparallel double δ-magnetic-barrier nanostructure, which is constructed on the surface of the InAs/AlxIn1-xAs heterostructure by patterning two ferromagnetic (FM) stripes. It is shown that the dwell time is dependent on electron spins due to the spin–field interaction between spins and magnetic fields. It is also shown that both magnitude and sign of the spin polarization in the dwell time can be modulated by the structural width or magnetic-strength difference between two magnetic barriers, which may give rise to a controllable temporal spin splitter for spintronics device applications. [ABSTRACT FROM AUTHOR]

The visible photoluminescence (PL) of ZnO is controversial for a long time. At present, the contribution of oxygen interstitial defects to yellow/orange emission from ZnO nanostructures is on debate. In this report, the origin of orange emission from solution-grown ZnO nanorods is investigated using excitation wavelength dependent photoluminescence PL, PL excitation and UV-Vis spectra. These results showed that orange emission may be due to the transition of an electron from shallow defect levels positioned slightly below the conduction band to the singly ionized oxygen vacancies. Hence, it is believed that oxygen interstitials may not be responsible for orange emission from solution grown ZnO nanostructures. [ABSTRACT FROM AUTHOR]

Magneto-optical spectroscopy based on the transverse magneto-optical Kerr effect (TMOKE) is a sensitive method for investigating magnetically-ordered media. Previous studies were limited to the weak coupling regime where the spectral width of optical transitions considerably exceeded the Zeeman splitting in magnetic field. Here, we investigate experimentally and theoretically the transverse Kerr effect in the vicinity of comparatively narrow optical resonances in confined quantum systems. For experimental demonstration we studied the ground-state exciton resonance in a (Cd,Mn)Te diluted magnetic semiconductor quantum well, for which the strong exchange interaction with magnetic ions leads to giant Zeeman splitting of exciton spin states. For low magnetic fields in the weak coupling regime, the Kerr effect magnitude grows linearly with increasing Zeeman splitting showing a dispersive S-shaped spectrum, which remains almost unchanged in this range. For large magnetic fields in the strong coupling regime, the magnitude saturates, whereas the spectrum becomes strongly modified by the appearance of two separate peaks. TMOKE is sensitive not only to the sample surface but can also be used to probe in detail the confined electronic states in buried nanostructures if their capping layer is sufficiently transparent.

Data on the synthesis of structures for a quantum cascade terahertz laser in the AlGaAs/GaAs material system on GaAs substrates using the molecular-beam-epitaxy method and their characterization are presented. The specific features necessary for the implementation of such structures are considered. It is shown that, for this configuration, almost single-mode lasing is observed at a frequency of ~3 THz up to a temperature of ~60 K. [ABSTRACT FROM AUTHOR]

Tin-oxide-based metal oxide nanoparticles synthesis method and characterization results are reported. These tin-oxide nanoparticles have been synthesized using the ultrasonic probe method. The morphology and surface characteristics of synthesized nanoparticles have been analyzed through electron microscopy and X-ray diffraction technique. The sensitivity of carbon dioxide gas detection has been tested using a sensing layer prototype. [ABSTRACT FROM AUTHOR]

Of all two-dimensional semiconductor crystals, WSe2 is particularly interesting due to its sizable bandgap, high carrier mobility, and compatibility with large-scale synthesis. By passivating WSe2 MOSFETs with atomic-layer-deposited Al2O3, they are stable in room environment for more than five months. The passivation also increases their current capacity by two orders of magnitude. Their cutoff frequencies peak around room temperature, with the forward current cutoff frequency ${f} _{T} \sim 0.6$ GHz and the maximum frequency of oscillation ${f} _{{\textit {MAX}}} \sim 2$ GHz. These results show WSe2 is a promising material for gigahertz thin-film transistors. However, if the surface passivation is not optimized, fixed charge in the passivation layer may lead to temporal and temperature instabilities. [ABSTRACT FROM AUTHOR]

The cost-effective production of chemicals in electrolytic cells and the conversion of the radiation energy into electrical energy in photoelectrochemical cells (PECs) require the use of electrodes with large surface area, which possess either electrocatalytic or photoelectrocatalytic properties. In this context nanostructured semiconductors are electrodic materials of great relevance because of the possibility of varying their photoelectrocatalytic properties in a controlled fashion via doping, dye-sensitization or modification of the conditions of deposition. Among semiconductors for electrolysers and PECs the class of the transition metal oxides (TMOs) with a particular focus on NiO interests for the chemical-physical inertness in ambient conditions and the intrinsic electroactivity in the solid state. The latter aspect implies the existence of capacitive properties in TMO and NiO electrodes which thus act as charge storage systems. After a comparative analysis of the (photo)electrochemical properties of nanostructured TMO electrodes in the configuration of thin film the use of NiO and analogs for the specific applications of water photoelectrolysis and, secondly, photoelectrochemical conversion of carbon dioxide will be discussed.

The available data on the photocatalytic activation of carbon monoxide are summarized. The most important directions of research and development in this area are examined. The related electronic processes are analyzed and reaction mechanisms in these systems are proposed. The most promising directions for further research in this area are indicated. [ABSTRACT FROM AUTHOR]

The purpose of this study is to formulate an Analytical model of equispaced energy levels quantum wells (QWs) in semiconductor ternary alloys (AxB1-xC). The procedure is by mapping the envelop function Schrodinger equation for realistic QW, with the local conduction band edge as the potential experienced by an electron in the QW into an effective mass Schrodinger equation with a linear harmonic oscillator potential by the method of coordinate transformation. The electron effective mass and potential are then obtained as the signature for the equispaced energy level for QWs in semiconductor ternary alloys. [ABSTRACT FROM AUTHOR]

We report on photoluminescence (PL) spectroscopy and transmission electron microscope imaging of suspended and substrate-supported flakes of the 2-D semiconductor MoS2 before and after exposure to 100-keV proton radiation with fluences of $6 \times 10^{13}$ , $6\times 10^{14}$ , and $6 \times 10^{15}$ p/cm2, respectively, and subsequent annealing. An indirect-to-direct bandgap transition is observed, which is preserved after annealing. This transition is accompanied by an unexpected increase in PL intensity after radiation exposure of multilayer samples, which is attributed to higher radiative efficiency of the direct-gap transition. [ABSTRACT FROM AUTHOR]

The term terahertz (THz) became one of the most popular words in science nowadays. Why? And what is it? Why more and more scientific books, articles, and conferences are being devoted to this topic all over the world? Why THz centers are being established at many universities and laboratories? Why do THz programs appear in different countries? The article brings you short answers to these questions. It explains what THz radiation is and what a so-called THz gap is. We touch the peculiarities of the THz radiation and mention its important applications. Then we consider the state of the art in THz science. As it is impossible to cover all the scientific and technical aspects of the THz science in the short review, therefore we only touch the semiconductor nanostructure-based devices and technologies in two most important fields; namely, we will look at THz sources and detectors, paying particular attention to their differences from conventional optical devices. And we hope that readers of this article will become more familiar with THz science and they will also try to find their own ways of implementing THz radiation into their scientific activities. Keywords: Terahertz radiation, semiconductor nanostructures, terahertz devices. Resumen El término terahertz (THz) se convirtió en una de las palabras más populares de la ciencia hoy en día. ¿Por qué? ¿Y qué es esto? ¿Por qué cada vez más libros, artículos y conferencias científicas se están dedicando a este tema en todo el mundo? ¿Por qué centros THz se están estableciendo en muchas universidades y laboratorios? ¿Por qué han aparecido programas académicos sobre THz en diferentes países? El artículo presenta respuestas breves a estas preguntas. En él se explica lo que es la radiación THz y que es la llamada brecha THz. Presentamos las peculiaridades de la radiación THz y mencionamos sus aplicaciones más importantes. Más adelante, describimos el estado del arte en la ciencia THz. En un artículo corto es imposible cubrir todos los aspectos científicos y técnicos de la ciencia THz, por lo tanto, restringiremos la discusión a los dispositivos y las tecnologías basadas en nanoestructuras semiconductoras en dos campos muy importantes a saber, las fuentes y detectores de THz; prestando especial atención a sus diferencias con respecto a los dispositivos ópticos convencionales. Esperamos que los lectores adquieran una familiaridad suficiente con la ciencia de THz y que traten de encontrar sus caminos propios para implementar la radiación THz en sus actividades científicas.

Silicon nanowire field-effect transistors (Si-NW FETs) have been demonstrated as a versatile class of potentiometric nanobiosensors for real time, label-free, and highly sensitive detection of a wide range of biomolecules. In this review, we summarize the principles of such devices and recent developments in device fabrication, fluid integration, surface functionalization, and biosensing applications. The main focus of this review is on CMOS compatible Si-NW FET nanobiosensors.

Solution-processed 2-D materials, being low temperature, low cost, and scalable, are attractive for future-generation thin-film and flexible transistors. However, it is challenging to dispense solution-processed 2-D material into a thin and continuous channel for effective and uniform gate control. In addition, a thick channel under the source and drain contacts is required to increase the transfer length and decrease the edge contact resistance. To overcome such a dilemma and to obtain the optimum combination of effective gate control and low contact resistance, channel recess was demonstrated for the first time on MoS2, so that the channel is thin in the gate region but thick in the source and drain regions. Specifically, channel recess by CHF3/O2 dry etching up to 60 s was performed on submicron buried-gate MOSFETs fabricated on 20-nm-thick spin-coated MoS2. It was found that the channel recess improved the current on/off ratio by 3 orders of magnitude while maintaining approximately the same contact resistance and peak transconductance as that of a uniformly 20-nm-thick channel. The resulted performance was among the best of all solution-processed MoS2 MOSFETs. The same channel recess technique can be used to improve the performance of MOSFETs made of other solution-processed 2-D materials. [ABSTRACT FROM AUTHOR]

Abstract: Publications of a number of countries on semiconductor nanostructures for 2000-2016 are analyzed on a bibliometric basis. The contribution of Russian participants in the studies and the structure of international scientific ties of domestic scientists are considered in detail. The initial array of the publications was extracted from the Science Citation Index Expanded database using relevant keywords. Information to analyze patent activity was taken from the data of the Russian Federal Service for Intellectual Property (Rospatent), US PTO, and WIPO PATENTSCOPE. [ABSTRACT FROM AUTHOR]