Semiconductor nanowires have continued to be an important material format for both fundamental science and device research. Recent years have witnessed a fantastic progress on semiconductor nanowires across different material systems, such as II-VI, III-V, III-nitrides, and so on. In this review paper, I would like to focus on some of the recent developments in III-nitride nanowires and their device applications. A specific III-nitride nanowire synthesis technique, molecular beam epitaxy (MBE), which is a highly controllable, scalable, and industrial production compatible material synthesis technique, is focused. Recent understanding about the MBE growth of IIInitride nanowires, including low temperature selective area epitaxy (SAE) and chamber configuration dependent properties, is discussed. Moreover, recent advances on III-nitride nanowire light-emitting and photodetection devices are discussed. In addition, emerging studies on scandium (Sc) incorporated III-nitride nanowires and devices are discussed. The intention of this review paper is to complement recent reviews in the field of III-nitride nanowire research and provide readers some future perspectives on this intriguing semiconductor material system.

Abstract We demonstrate a high-operating-temperature short-wave infrared detector based on a simple p-Ge 1-x Sn x /n-Ge junction structure. A pseudomorphic Ge 1-x Sn x thin film with 7.0% Sn composition was epitaxially grown on an n-type Ge substrate using molecular beam epitaxy. The fabricated photodetector was evaluated using a high-precision photocurrent measurement system based on FTIR spectroscopy, which enables signal detection over more than four orders of magnitude. The device exhibited a photoresponse extending up to 2.4 μm at room temperature and achieved a spectral detectivity exceeding 10 8 cmHz 1/2 /W at 2 μm under 240 K operation. The detector also demonstrated low dark current and stable responsivity under reverse bias, indicating effective noise suppression without the need for complex cooling systems. These results highlight the potential of Ge 1-x Sn x -based detectors for compact, low-cost, and multi-band infrared imaging applications.

We investigate the amorphous-to-crystalline transformation of antimony selenide (Sb2Se3) on UHV-prepared GaAs (001) substrates. In the bulk orthorhombic form, Sb2Se3 is a layered quasi-1D semiconductor with highly anisotropic properties of interest for optical and electronic devices. We find that an amorphous layer deposited by molecular beam epitaxy annealed at or above 230 °C yields a textured-epitaxial structure among some randomly oriented domains. The textured-epitaxial Sb2Se3 grains are oriented with the covalently bonded “1D axis” constrained in-plane to GaAs [110] and with multiple van der Waals (hk0) orientations out-of-plane. The same texture was achieved exclusively without randomly oriented grains using continuous-wave laser radiation, highlighting the use of thermal and optical methods to yield anisotropic crystalline Sb2Se3 films directly from the amorphous phase. Polarized reflectance and polarized microscopy confirm the unique state of in-plane birefringence in the crystallized thin film. Overall, we show that solid-phase heteroepitaxy provides additional pathways to the integration of low-symmetry chalcogenide semiconductors for demanding applications where the inherent anisotropy needs to be preserved.

The superlattice engineering approach has proven effective in synergistically improving physical properties of multifunctional materials, yet its application in GeTe-based films remains unexplored. In this work, we fabricated (1T'-MoTe2)x/(GeTe)y superlattice films with well-controlled periodic layering and good structural coherence periodicity via molecular beam epitaxy, demonstrating the simultaneous optimization of thermoelectric and ferroelectric properties through superlattice engineering. The improved thermoelectric performance in GeTe-based superlattices arose from the evolution of intrinsic point defects, interfacial charge transfer, and band-bending-induced energy filtering. Specifically, the (1T'-MoTe2)2/(GeTe)80 film achieved a high carrier effective mass of 3.70 m* and a superior room-temperature power factor of 2.53 mW m-1 K-2, arising from an optimal balance between enhanced effective mass and hole density. Meanwhile, the (1T'-MoTe2)2/(GeTe)30 film exhibited markedly enhanced ferroelectric polarization as compared to the pristine GeTe film, with a large piezoelectric coefficient (d33) of 15.3 pm V-1, which is likely attributed to interfacial charge-transfer-induced suppression of the depolarization field. This work highlights the efficacy of superlattice engineering in concurrently optimizing thermoelectric and ferroelectric properties of GeTe-based films, offering insights on performance optimization of multifunctional materials.

Selective facet exposure in two-dimensional (2D) materials is highly sought after but typically achieved using complex techniques such as Molecular Beam Epitaxy (MBE) or Chemical Vapor Deposition (CVD). Existing wet-chemical...

As promising candidates for two-dimensional (2D) magnetic semiconductors, layered transition metal halides (TMHs) have attracted increasing interest due to their diverse insulating bandgaps and magnetic properties. Here, we report the epitaxial growth of atomically thin MnBr2 films on Au(111) by molecular beam epitaxy (MBE). Scanning tunneling microscopy (STM) reveals the initial formation of different buffering layers with distinct atomic structures on the Au(111) surface, followed by the subsequent growth of MnBr2 layers. X-ray photoelectron spectroscopy (XPS) confirms that Mn atoms are in different coordination environments in the buffering layers (MnBrx, x < 2) from MnBr2 crystals. The electronic properties of MnBr2 thin films with different thicknesses are investigated by scanning tunneling spectroscopy (STS) and density functional theory (DFT) calculations, showing that the electronic band structures are nearly independent of the thickness and the Au(111) substrate. This study provides a better insight into the growth behavior and interfacial properties of 2D layered TMHs on metal substrates.

Topotaxy of 2D materials by reacting a van der Waals-material with a transition metal is a potential approach for accessing compositional 2D variants. Here, the synthesis of a 2D-NiPtTe2 alloy is demonstrated by incorporating Ni into PtTe2. The Pt-telluride system exhibits two 2D phases, a di-telluride (PtTe2) and mono-telluride (Pt2Te2). By reacting PtTe2 with Ni the system transforms into a NiPtTe2, i.e. the monotelluride phase with two transition metals per unit cell in an ordered alloy structure. The samples are grown by molecular beam epitaxy and characterized by low energy electron diffraction, X-ray photoemission spectroscopy, and scanning tunneling microscopy. Studies are performed on both multilayer PtTe2 films as well as monolayer samples. On multilayers the transformation is more complex and different phases can coexist. In monolayers a phase separation into pure PtTe2 and the Ni-modified NiPtTe2 phase is observed, indicating that both are low energy configurations. The formation energy of various structures with different Ni-composition is also evaluated by density functional theory calculations confirming that the mixed NiPtTe2 phase is favored over other configurations, particularly the intercalation of Ni in between PtTe2 layers is shown to be less favorable.

Vibrational sum frequency generation spectroscopy reveals the inertness of chromium oxide (001) surfaces.

During the growth of monolayer MoS2-TaS2 heterostructures, we observe the Kirkendall effect, a phenomenon not previously reported in systems with reduced dimensionality. The lateral heterostructures were prepared by reactive molecular beam epitaxy on chemically inert and weakly interacting Au(111). Enclosing MoS2 islands in TaS2 by exposing them to a sulfur-rich environment at elevated temperatures facilitates diffusion at the interface. The resulting heterostructures exhibit characteristic 2D Kirkendall voids surrounded by a MoxTayS2 alloy region. These findings reveal defect-mediated processes in low-dimensional systems and open new avenues for designing 2D lateral heterostructures with intricate morphologies.

We report the successful growth of stoichiometric, epitaxial ytterbium nitride (YbN) thin films via molecular beam epitaxy under ultrahigh vacuum conditions using activated nitrogen supplied by a plasma source. Through systematic optimization of the growth parameters, we achieved high-quality YbN films with excellent crystallinity and a well-defined (100) out-of-plane orientation on MgO(100) and LaAlO 3 (100) substrates, as determined by reflection high-energy electron diffraction and x-ray diffraction. In photoelectron spectroscopy results unambiguously demonstrate the semiconducting character of YbN and the fully trivalent valence state of the Yb ions. Using the photon-energy dependence of the valence band spectra we were able to reveal a significant hybridization between the Yb 4 f and N 2 p states.

Epitaxy of highly strained InGaAs quantum wells with a mole fraction of indium exceeding 35 % is a technologically challenging task. The structural quality of these elastically strained epitaxial layers greatly affects the photoluminescence efficiency of quantum wells. Therefore, in order to achieve high structural quality, optimization of the epitaxial growth parameters is required, one of which is the growth rate of the epitaxial layer. Heterostructures containing the In x Ga 1–x As (0.37 ≤ x &lt; 0.41) quantum well were produced on GaAs substrates by molecular beam epitaxy with different growth rates of InGaAs ranging from 0.24 to 3.3 Å/s. The actual thickness and composition of the quantum well were determined by X-ray diffractometry, as well as the structural quality of the heterostructures was investigated. The photoluminescence spectra of the manufactured heterostructures were measured at temperatures of 20 K and 300 K at different optical pumping powers. Based on the dependence of photoluminescence intensity on pumping power, recombination currents were calculated and the time of non-radiative recombination in the studied structures was estimated. The InAs content in the quantum wells of the manufactured heterostructures ranged from 37.0 % to 40.6 %. Based on analysis of X-ray rocking curves, deterioration of structural quality at low deposition rate of 0.24 Å/s was observed. The photoluminescence spectroscopy measurements showed a significantly higher photoluminescence intensity of quantum wells at moderate growth rates of InGaAs (0.9–2.5 Å/s) compared to other samples. The calculated values for the non-radiative recombination lifetime of quantum wells produced at these moderate growth rates were in the order of 10 –6 s at 20 K and 10 –9 s at 300 K. At higher or lower growth rates, the values of the non-radiative recombination lifetime decreased. The results obtained demonstrate the achievement of the best structural quality for highly strained InGaAs layers produced at 0.9–2.5 Å/s growth rate. These results can be used to optimize the parameters of epitaxial growth processes for highly strained quantum wells based on InGaAs, for fabricating monolithic vertical-cavity surface-emitting lasers, based on GaAs substrate, operating in the 1200–1300 nm spectral range.

Recently, there has been much interest in the ScAlN alloy, thanks to its various potential applications in high-frequency high-power, acoustoelectric, and ferroelectric devices. Nonetheless, these applications could be impaired by the presence of oxygen in the alloy and the formation of a surface oxide layer due to the high affinity of scandium with such impurity. A current trend is to increase the Sc content and most of the time it is accompanied by a lowering of the growth temperature. As it probably strongly influences the incorporation of impurities, we have carefully studied the effects of growth temperature and Sc content in the surface oxide and oxygen content of ScAlN films grown by ammonia source molecular beam epitaxy. The oxygen concentration and bonding configuration have been determined by combining normal-incidence, angle resolved, and ion-etching x-ray photoelectron spectroscopy.

III-nitride semiconductors are emerging as promising thermoelectric (TE) materials when integrated with III-nitride optical and electronic devices for exhaust heat management. Among these, InGaN has been predicted to exhibit high thermoelectric performance. However, comprehensively evaluating the TE properties of InGaN across the full In content range is challenging owing to difficulties in crystal growth, especially at higher In contents. In this study, InGaN was grown over the entire In content range using radio frequency plasma-assisted molecular beam epitaxy. Optimizing the growth temperature and maintaining the flux relationship of In + Ga &amp;gt; N* &amp;gt; Ga enabled the growth of InGaN films with smooth surfaces, single In content, and c-axis orientation. A high-quality InN film was also achieved through droplet elimination by radical beam irradiation method, effectively eliminating In droplets on the growing surface. The surface flatness and crystal coherency of InGaN degraded in the mid-range of In content, reflecting the thermodynamic instability characteristic of immiscible alloy systems. With increasing In content, the absolute value of the Seebeck coefficient decreased, while electrical conductivity, Hall mobility, and carrier concentration increased. These trends were consistent with the previously reported calculated values. The discrepancies between experimental results and calculation are discussed in terms of carrier and phonon scattering, linked to crystal quality such as surface flatness, dislocation density, and impurity concentration. Although the maximum power factor was observed in InN, the highest dimensionless thermoelectric figure of merit (ZT) was obtained for In0.8Ga0.2N, attributable to the reduction in thermal conductivity (κ) through alloy scattering.

By employing graded-interfaces modeling, ~10 μm-emitting quantum cascade lasers (QCLs) are designed with previously found conditions for record-high wall-plug efficiency (WPE) operation of mid-infrared QCLs: direct resonant-tunneling injection from a prior-stage low-energy state into the upper-laser level, photon-induced carrier transport, and carrier-leakage suppression via the step-taper active-region (STA) approach. For devices with interface-roughness (IFR) parameters characteristic of optimized molecular-beam-epitaxy (MBE) growth, a maximum front-facet pulsed WPE value of 19.6% is projected for 60-stages STA-type devices. This results from several factors: 19 mV voltage defect at threshold, 72% voltage efficiency at the maximum WPE point, and ~93% injection efficiency due to strong carrier-leakage suppression. 2.7 W peak front-facet power is projected. For devices with our metal–organic chemical vapor deposition (MOCVD)-growth IFR parameters, the projected maximum pulsed WPE value is 17.1%, i.e., 1.7 times higher than the highest reported front-facet WPE value from ~10 μm-emitting MOCVD-grown QCLs. Studies regarding the WPE value variation with the stage number, while employing waveguide designs having the same empty cavity loss, reveal that the maximum WPE value remains almost the same for 50–60 stages devices. In turn, there is potential for obtaining significantly higher CW powers than from conventional ~10 μm-emitting QCLs.

We have studied the growth of barium tungstate, BaWO4, by high-temperature oxygen-assisted molecular beam epitaxy on W(110). Barium tungstate grows in the form of isosceles triangular-shaped islands, tens of micrometers wide and tens of nanometers in height. The growth was monitored in real time by low-energy electron microscopy and characterized in situ by low-energy electron diffraction, X-ray absorption and X-ray photoelectron spectroscopies. Further ex situ characterization was performed by optical and atomic force microscopies and Raman spectroscopy. Barium tungstate growth on W(110) was performed by dosing only barium in a molecular oxygen atmosphere due to incorporation of W atoms from the W(110) substrate. The islands correspond to the BaWO4 (011) crystallographic orientation and their sides are aligned along the [001] and [11̄1] directions of the BaWO4 crystal.

We demonstrate high-performance MOSFETs on β-Ga2O3 films grown by plasma-assisted molecular beam epitaxy (PA-MBE). The high crystalline quality of the β-Ga2O3 epilayer was confirmed by X-ray diffraction and atomic force microscopy. An optimized CF4-plasma treatment was employed to introduce fluorine (F) into the near-surface region, effectively suppressing donor-like states. The resulting devices exhibit an ultralow off-state current of 1 × 10−9 mA/mm and a stable on/off ratio of 105. A controllable positive threshold voltage shift up to +12.4 V was achieved by adjusting the plasma duration. X-ray photoelectron spectroscopy indicates that incorporated F atoms form F–Ga-related bonds and compensate oxygen-related donor defects. Sentaurus TCAD simulations reveal reduced near-surface charge and a widened depletion region, providing a physical explanation for the experimentally observed increase in breakdown voltage from 453 V to 859 V. These results clarify the role of fluorine in modulating surface defect states in PA-MBE β-Ga2O3 and demonstrate an effective route for threshold-voltage engineering and leakage suppression in Ga2O3 power devices.

The crystal structure and thermoelectric parameters (conductivity, Seebeck coefficient, and power factor) of ultrathin (3–3.5 nm) stoichiometric monoclinic FeSi (m-FeSi) films and cubic FeSi (c-FeSi) films, as well as thin (14–49 nm) cubic FeSi (c-FeSi) films, were determined in the temperature range of 100–450 K. Single-phase FeSi films exhibit a metal-semiconductor transition at temperatures below 200 K due to the Kondo effect, metallic conductivity at temperatures below 30 K, and demonstrate a noticeable Seebeck effect in the range of 100–450 K. The thermoelectric parameters were calculated using a two-layer model for FeSi thin films and taking into account the film-to-substrate resistance ratio to minimize the substrate shunting effect. The 20–49 nm thick c-FeSi films (grown by molecular beam epitaxy) exhibit nearly the lowest resistivity, a positive Seebeck coefficient (30–85 μV/K), and a power factor [0.3–1.0 mW/(m K2)] in the range of 120–470 K. The phonon band structure and lattice thermal conductivity were calculated for both bulk c-FeSi and its nanowires. It was found that the lattice thermal conductivity of nanowires is four to ten times lower than that of bulk c-FeSi. The dimensionless thermoelectric figure of merit (ZT) of the thin FeSi films was estimated: the maximum ZT = 0.03–0.05 at 200–470 K was achieved for a 20 nm thick p-type c-FeSi film. This c-FeSi film was doped with boron atoms from the p+ layer of the Si substrate.

We review progress on the growth and device performance of InP quantum dot lasers emitting in the red spectral region. InAs quantum dot lasers with emission at 1.3 μ m are the most heavily developed quantum dot devices due to their potential for temperature-insensitive operation in optical data communication applications. However, InP quantum dot lasers have become the subject of renewed interest due to the advent of low-loss visible integrated photonic platforms with applications in quantum information, biosensing, and virtual/augmented reality displays. High-performance devices have been grown by both metalorganic chemical vapor deposition and molecular beam epitaxy, and we review the strengths and challenges of each growth technique. Like their InAs counterparts, InP quantum dot lasers have also proven to be tolerant of crystalline defects, making them amenable to monolithic integration on lattice-mismatched substrates such as silicon. Finally, we discuss promising directions for future work in the field, including surface-emitting lasers, mode-locked lasers, and methods of expanding the range of emission wavelengths to both shorter and longer wavelengths.

Optoelectronic devices based on AlGaN alloys find a wide range of applications, such as water and surface purification, solar-blind photodetection, and skincare. The energy bandgap of the alloy is a critical input parameter for the design of such devices. However, widely different values for the bowing parameter exist in the literature. In addition, data for AlGaN alloys with high AlN mole fractions are relatively sparse. In this work, AlGaN alloys covering the entire range of compositions from GaN to AlN were grown by molecular beam epitaxy, and their compositions and optical absorption edges were estimated and compared to the existing literature. While for alloys with lower AlN mole fractions, we report a bowing parameter similar to established values, a large variation was observed for AlN mole fractions higher than 60%, where the bowing parameter increased significantly. Overall, three different bowing parameters were identified across the entire composition range. Alloy disorder of these AlGaN films was estimated by computing their Urbach energies, and their dependence on the alloy composition also exhibits a significant increase for these high Al containing films. While the exact reason for this phenomenon remains unclear, the growth mode employed, and the presence of alloy phenomena such as atomic ordering and compositional inhomogeneities in the material may play a major role. These results are expected to be useful in the design of optoelectronic devices for deep ultraviolet applications, including light emitting didoes for skin-safe germicidal action.

The operational requirements of high-radiation and extraterrestrialenvironments highlight the need to evaluate narrow-bandgap semiconductorsthat remain unexplored under such conditions, among them Indium Antimonide(InSb). As a material system, InSb offers unparalleled electron mobilityand a massive g-factor, making it indispensable fornext-generation infrared detection, Hall sensing, and topologicalquantum computing architectures. However, the practical realizationof these devices is frequently hindered by the necessity of heteroepitaxialgrowth on lattice-mismatched substrates, typically Gallium Arsenide(GaAs), which introduces a complex landscape of threading dislocationsand interfacial defects. This report presents an exhaustive, multimodalinvestigation into the radiation hardness of InSb epilayers, specificallycontrasting the microstructural evolution of films grown via Metal–OrganicChemical Vapor Deposition (MOCVD) against those synthesized by MolecularBeam Epitaxy (MBE). Utilizing an experimental framework that integratesElectron Paramagnetic Resonance (EPR), Raman spectroscopy, High-ResolutionScanning Transmission Electron Microscopy (HR-STEM), and ab initioDensity Functional Theory (DFT), this study elucidates the mechanisticdivergence in radiation response between the two growth methodologies.The data reveal a critical, counterintuitive trade-off: the MOCVD-grownmaterial, despite exhibiting superior initial crystalline qualitydriven by a zinc-doped seed layer that passivates interfacial traps,demonstrates a heightened susceptibility to electronic degradationand stoichiometry violation under high-fluence Gamma (γ) irradiation.In contrast, the MBE-grown material, initially marred by a higherdensity of dislocations, exhibits a complex “survivability”mode at elevated doses, characterized by defect saturation. This reportdetails the atomic-level physics driving these behaviors, includingthe radiation-induced formation of homopolar Sb–Sb bonds, thesymmetry-breaking anisotropy of the g-factor, andthe thermodynamic instability of dopant-passivated interfaces undernonequilibrium conditions. Furthermore, these findings can be usedas actionable engineering guidelines for Radiation Hardness Assurance(RHA), proposing novel nondestructive spectroscopic metrics for thequalification of semiconductors destined for space and nuclear applications.