Molecular beam epitaxy

In the present work, analytical expressions for the energy eigenvalues and eigen functions are obtained by solving the radial Schrödinger equation for inverse quadratic Hellmann plus Yukawa (IQHY) potential using Nikiforov-Uvarov functional analysis method. As an application part of this work, expressions for the linear and third-order nonlinear absorption coefficients and refractive index changes are computed to study the optical properties of the spherical GaAs quantum dots. We extend the investigation of the IQHY potential by incorporating the effects of magnetic and Aharonov–Bohm (AB) flux fields. Our results reveal that the optical properties of the GaAs quantum dots are strongly influenced by variations in the dot radius, potential height and intensity of incident photons. Specifically, we observe that the introduction of magnetic and AB flux fields significantly alters the energy eigenvalues and eigenfunctions, leading to distinct optical characteristics. The results of present study are found in consistent with other theoretical studies available in the literature.

The crystallographic, optical, and electrical properties of manganese sulfide thin films depend on the control of the temperature precursors in the synthesis process, as shown by the results of this work. MnS thin films were deposited on glass substrates using the SILAR method and over an additional layer of CdS synthesized by chemical bath deposition (CBD) to acquire a p-n heterojunction. SILAR is an inexpensive method performed with a homemade robot in this case. Temperature in the solution precursors varied from 20 to 80 °C in four experiments. The morphology and structure of MnS and FTO/CdS/MnS thin films were studied through scanning electron microscopy (SEM) and grazing-incidence X-ray diffraction (GIXRD); the results indicate that materials showed a polycrystalline behavior, a diffraction peak of α- MnS cubic phase was observed with lattice constants values, ranging from 4.74 to 4.75 Å.

Additionally, Raman spectroscopy showed a signal corresponding to the transversal optical phonons of MnS at a wavenumber near 300 cm⁻¹. UV–vis spectroscopy showed optical bandgap values of 3.94, 4.0, 4.09, and 4.26 eV for thin films obtained at 20°, 40°, 60°, and 80 °C.

respectively. Results indicated 80 °C as an optimal cationic precursor process temperature, achieving optical transmittance T% and good film quality according to SEM and GIXRD for the synthetization of MnS. The current–voltage (I–V) characterization in the heterojunction showed a characteristic diode curve with an open circuit voltage (VOC) of 300 mV under illumination, which indicated that the manganese sulfide behaves as p-type material contributing with positive charge carriers, while CdS behaves as n-type material.

We report on a dramatic effect of the surface reconstruction of the substrate on thin film growth. We prepared two types of surface reconstruction, namely 2 × 1 and (√13 × √13)-R33.7° reconstructions, by annealing the SrTiO₃(001) substrates in ultrahigh vacuum (UHV) and an oxygen environment, respectively. Subsequent co-depositions of Fe and Se atoms onto the 2 × 1 and (√13 × √13)-R33.7° reconstructed SrTiO₃ surfaces lead to the growth of thin films of distinct six-fold and four-fold symmetry, respectively, under nominally the same growth conditions. Based on in-situ angle-resolved photoemission spectroscopy (ARPES) measurements of the electronic structure, we ascribe the aforementioned two types of thin film to the reported hexagonal and tetragonal phases of FeSe, respectively. The observation of the growth of hexagonal FeSe on the tetragonal SrTiO₃ surface with a 2 × 1 reconstruction is unexpected, the underlying mechanism of which remains an outstanding puzzle. Our finding adds a new dimension to the material phase control via the choice of surface reconstruction of the substrate used for thin film growth.

Epitaxial semiconductor quantum dots have been, in the last 40 years or so, at the center of the research effort of a large community. The focus being on “semiconductor physics and devices”, in view of the broad applications and potential, e.g., for efficient temperature insensitive lasers at telecom wavelengths, or as “artificial atoms” for quantum information processing. Our manuscript aims at addressing, with an historical perspective, the specifics of (III-V) epitaxial quantum dot early developments (largely for light emitting) and subsequent years. We will not only highlight the variety of epitaxial structures and methods, but also, intentionally glancing a didactic approach, discuss aspects that are, in general, little acknowledged or debated in the present literature. The analyses will also naturally bring us to examine some of current challenges, in a field which, despite sensational achievements, is, remarkably, still far from being mature in its developments and applications.

The proliferation of industrial units across the world for a diverse range of applications has culminated in the production of a massive number of contaminants that have a negative impact on both the health of humans and the environment. In this regard, the use of semiconductors in photocatalytic procedures is considered an emerging and promising approach for both the removal and mineralization of a wide range of pollutants. This review deliberates on assorted semiconductor catalysts, their preparative methods, and the underlying mechanisms involved; suggestions are advanced for improving the efficiency of semiconductors when used in the photocatalytic processes. In the following section, a variety of pollutants, comprising organic compounds, heavy metals, pharmaceutical contaminants, pesticides, and microorganisms, are discussed, wherein the recent applications of semiconductors in photocatalytic remediation are highlighted in tabular forms.

This study investigated the molecular beam epitaxy (MBE) growth conditions of strain-balanced (SB) In_0.669GaAs/In_0.362AlAs superlattices (SLs) for SB quantum cascade lasers (QCLs). The growth modes and properties of SB SLs are strongly affected by the growth conditions. The properties of the SB SLs were evaluated using atomic force microscopy (AFM) and high-resolution X-ray diffraction (HRXRD) analysis. Following the establishment of optimized conditions for SB SLs growth, SB QCL were grown. The HRXRD analysis and transmission electron microscopy (TEM) measurements showed that the grown samples exhibited abrupt interfaces and good structural quality. An epitaxial wafer was processed into a Fabry-Perot cavity with a ridge structure. The device operated in pulsed mode emitting ∼4.7 µm at room temperature with a peak power of 650 mW and a slope efficiency of 870 mW/A.