Search

The large coercive electric field is the main obstacle for the application of wurtzite ferroelectrics in the memory devices. To explore the effective methods to reduce the coercive electric field of wurtzite ferroelectrics, in this work, after screening a series of possible candidates, (MC)1/(AlN)n (M = Ti, Zr) superlattices and anion P-doping are both chosen to regulate the switching energy barrier of wurtzite AlN based on the density functional theory calculations. It is found that the polarization switching energy barriers of wurtzite AlN gradually decrease by increasing the ratio of the MC (M = Ti, Zr) layer. When the ratio of the MC layer is up to 33%, the polarization switching energy barriers of (TiC)1/(AlN)n and (ZrC)1/(AlN)n are decreased by 68% and 55%, respectively, compared with that of pure wurtzite AlN. The anionic P-doping in AlN results in a 48% lower energy barrier. Also, the ferroelectric polarization in the designed superlattices and P-doped AlN is well maintained compared to pure AlN. Thus, the results show that the (MC)1/(AlN)n (M = Ti, Zr) superlattices and anion P-doping approaches are effective in improving the polarization switching properties of wurtzite AlN. [ABSTRACT FROM AUTHOR]

Injection of interstitial atoms by specially prepared surfaces submerged in liquid water near room temperature offers an attractive approach for post-synthesis defect manipulation and isotopic purification in device structures. However, this approach can be limited by trapping reactions that form small defect clusters. The compositions and dissociation barriers of such clusters remain mostly unknown. This communication seeks to address this gap by measuring the dissociation energies of oxygen interstitial traps in rutile TiO2 and wurtzite ZnO exposed to liquid water. Isotopic self-diffusion measurements using 18O, combined with progressive annealing protocols, suggest the traps are small interstitial clusters with dissociation energies ranging from 1.3 to 1.9 eV. These clusters may comprise a family incorporating various numbers, compositions, and configurations of O and H atoms; however, in TiO2, native interstitial clusters left over from initial synthesis may also play a role. Families of small clusters are probably common in semiconducting oxides and have several consequences for post-synthesis defect manipulation and purification of semiconductors using submerged surfaces. [ABSTRACT FROM AUTHOR]

Wurtzite ScxAl1−xN/GaN (x = 0.13–0.18) multi-quantum wells grown by molecular beam epitaxy on c-plane GaN are found to exhibit remarkably strong and narrow near-infrared intersubband absorption in the technologically important 1.8–2.4 μm range. Band structure simulations reveal that, for GaN wells wider than 3 nm, the quantized energies are set by the steep triangular profile of the conduction band caused by intrinsic polarization fields. As a result, the intersubband transition energies provide unique and direct access to essential ScAlN polarization parameters. Measured infrared absorption indicates that the spontaneous polarization difference of the presumed lattice-matched Sc0.18Al0.82N/GaN heterostructure is smaller than the theoretically calculated value. The intersubband transition energies are relatively insensitive to the barrier alloy composition indicating negligible variation of the net polarization field in the probed 0.13–0.18 Sc composition range. [ABSTRACT FROM AUTHOR]

In this work, the value and the polarity of the spontaneous and piezoelectric polarization have been investigated, as the use of two different reference structures for wurtzite-type group-III nitrides, namely, the zinc-blende and the layered-hexagonal crystal lattice, have resulted in different predictions. It was found that although the differences in value and polarity of the polarization for heterostructures such as wurtzite Al1−xScxN/GaN lead to similar interface sheet charges, a significant mismatch is observed when polarization reversal is considered. The interface sheet charge predicted before and after the polarization reversal in the wurtzite Al1−xScxN layer on GaN using the zinc-blende lattice as a reference predominantly shows a change in sign. When using the layered-hexagonal lattice as a reference, not only is the same polarity of the interface sheet charge maintained after polarization reversal, but it is even 30 times larger. In this case, the giant and positive spontaneous polarization values for metal-polar Al1−xScxN extracted from the ferroelectric switching, as well as the alignment of the piezoelectric polarization to it, were observed to be consistent with the predictions referenced to the layered-hexagonal lattice. Thus, it is concluded that the layered-hexagonal reference is not only more suitable for predicting the ferroelectric properties of wurtzite Al1−xScxN but should also be the correct reference when considering polarization reversal in heterostructures. If the significant increase in the interface sheet charge after polarization reversal is experimentally detected, it will allow the design and fabrication of novel devices for future high-frequency and power electronics applications. [ABSTRACT FROM AUTHOR]

A first-principles-based lattice model is applied to investigate the ordered phases of mixed group-III nitride ternary alloys. The model surveys the atomistic configurations with the lowest formation enthalpy for a wide range of compositions. We found novel ordered phases in wurtzite structures having specific compositions of three- and four-sevenths molar fractions of group-III cations. The configurations of group–III atoms on cation sites in those phases consist of a characteristic fragment of the ordered phases of one-third and one-half ordered phases that were previously reported. The simulation results indicate that group-III cations in ternary nitrides follow spatial positioning "atomistic distancing rules" that can be described by the pairwise interaction energy of group-III cations to realize the stabilities of the ordered structures. To minimize the formation enthalpy of a mixed crystal, the minor B, Al, Ga, and In atoms on cation sites remain neither too close to nor too distant from each other, allowing those ordered phases to be realized. [ABSTRACT FROM AUTHOR]

A Landau–Devonshire thermodynamic energy density function for ferroelectric wurtzite aluminum scandium nitride (Al1−xScxN) solid solution is developed. It is parametrized using available experimental and theoretical data, enabling the accurate reproduction of composition-dependent ferroelectric properties, such as spontaneous polarization, dielectric permittivity, and piezoelectric constants, for both bulk and thin films. The maximum concentration of Sc for the wurtzite structure to remain ferroelectric is found to be 61 at. %. A detailed analysis of Al1−xScxN thin films reveals that the ferroelectric phase transition and properties are insensitive to substrate strain. This study lays the foundation for quantitative modeling of novel ferroelectric wurtzite solid solutions. [ABSTRACT FROM AUTHOR]

Thermal transport in wurtzite aluminum nitride (w-AlN) significantly affects the performance and reliability of corresponding electronic devices, particularly when lattice strains inevitably impact the thermal properties of w-AlN in practical applications. To accurately model the thermal properties of w-AlN with high efficiency, we develop a machine learning interatomic potential based on the atomic cluster expansion (ACE) framework. The predictive power of the ACE potential against density functional theory (DFT) is demonstrated across a broad range of properties of w-AlN, including ground-state lattice parameters, specific heat capacity, coefficients of thermal expansion, bulk modulus, and harmonic phonon dispersions. Validation of lattice thermal conductivity is further carried out by comparing the ACE-predicted values to the DFT calculations and experiments, exhibiting the overall capability of our ACE potential in sufficiently describing anharmonic phonon interactions. As a practical application, we perform a lattice dynamics analysis using the potential to unravel the effects of biaxial strains on thermal conductivity and phonon properties of w-AlN, which is identified as a significant tuning factor for near-junction thermal design of w-AlN-based electronics. [ABSTRACT FROM AUTHOR]

The material dependence of phonon-polariton-based in-plane thermal conductance is investigated by examining systems composed of air and several wurtzite and zinc-blende crystals. Phonon-polariton-based thermal conductance varies by over an order of magnitude (∼ 0.5 – 60 nW/K), which is similar to the variation observed in the materials corresponding to bulk thermal conductivity. Regardless of the material, phonon-polaritons exhibit similar thermal conductance to that of phonons when layers become ultrathin (∼ 10 nm), suggesting the generality of the effect at these length-scales. A figure of merit is proposed to explain the large variation of in-plane polariton thermal conductance that is composed entirely of easily predicted and measured optical phonon energies and lifetimes. Using this figure of merit, in-plane phonon-polariton thermal conductance enlarges with increases in (1) optical phonon energies, (2) splitting between transverse and longitudinal mode pairs, and (3) phonon lifetimes. [ABSTRACT FROM AUTHOR]

Metal oxide-based nanocomposites has been regarded as a useful tool for sensors technology to detect various hazardous gases at low concentrations. In this work, the CeO2–ZnO composite was successfully synthesized using a simple chemical combustion method. The synthesized samples were characterized by employing different characterization techniques. The results demonstrated that the cubic fluorite phase of CeO2 and the hexagonal wurtzite phase of ZnO have been obtained while the CeO2–ZnO composite showed a mixed phase of CeO2 and ZnO. The morphology of the CeO2–ZnO products has a nanoporous structure. The well-defined structure of the CeO2–ZnO nanocomposite was confirmed by the HR-TEM. Furthermore, gas sensing study showed that CeO2–ZnO nanocomposite exhibited enhanced sensing properties toward ethanol at an operating temperature of 275 ℃. The gas sensitivity value was 61.75% toward 24 ppm ethanol. This could be attributed to the formation of the n–n heterojunction between CeO2 and ZnO which enhances conductivity value to give more sensitivity. [ABSTRACT FROM AUTHOR]

Electronic properties of intrinsic ZnO, N‐doped ZnO, and Al–N‐codoped ZnO of both hexagonal wurtzite (HW) and zincblende (ZB) structures are investigated by first‐principles calculations. Both N‐doped ZB‐ZnO and N‐doped HW‐ZnO achieve p‐type transition by the introduction of N‐2p states, forming shallow acceptor levels above the valence band. However, the positive impurity formation energy implies the difficulty and instability of N‐doped ZnO. In Al–N‐codoped ZnO, the Al elements compensate the p‐type doping effect, but partially enhance the solubility of N. Furthermore, the comparison of the electronic properties between HW‐ZnO and ZB‐ZnO indicates that the ZB structure favors the achieving of p‐type doping. [ABSTRACT FROM AUTHOR]

The electronic intrinsic surface states in wurtzite Zn-IV-N2 (with group- IV = Sn , Ge and Si) semiconductors were investigated using an intermediate-coupling variational approach considering the electron–surface optical phonon interaction influence. The intrinsic surface state energy distribution and the average penetrating depth of surface state eigen-wave function of the electron have been evaluated numerically by changing the surface potential barrier V 0 for wurtzite ZnSnN2, ZnGeN2 and ZnSiN2, respectively. The results show that the electronic intrinsic surface state energy increased linearly with increasing surface potential barrier V 0 for all the calculated materials. The result also indicated that the electronic intrinsic surface state energies variations due to the influence of electron–surface optical phonon interaction are dozens of meV. The average penetrating depth of electronic surface state eigen-wave function is independent of V 0 . Its value is no more than the corresponding material's lattice constant. The electronic scattering by surface optical phonon should be taken into account in the study of the intrinsic surface state of electrons in the group of Zn-IV-nitrides (with IV = Sn , Ge and Si) semiconductors, especially for materials having strong electron–phonon interaction and wide band gap. [ABSTRACT FROM AUTHOR]

Reducing the reversal barrier of Al1−xScxN ferroelectric alloy is critical for improving the coercive voltage and power consumption of ferroelectric devices. Here, the synergistic effect of alloy composition and strain is introduced to optimize the ferroelectric properties of Al1−xScxN alloys. Because of the increased Al–N ionic bond character and the contribution of Sc-d orbitals, the spontaneous polarization, reversal barrier, and bandgap all reduce as the Sc concentration increases. Strain engineering improves the electron's electric dipole moment, resulting in a significant increase in spontaneous polarization (145.93 μC/cm2 for Al0.625Sc0.375N alloy). Meanwhile, the horizontal tension and vertical compression lower the reversal barrier of Al0.625Sc0.375N alloy to 95.45 meV/f.u., significantly lower than that of orthorhombic HfO2. Interestingly, the bandgap of Al1−xScxN alloy with low Sc concentration rises initially and then decreases as horizontal strain varies from compression to tension, whereas that of Al1−xScxN alloy with high Sc concentration monotonically decreases. The Al1−xScxN alloy exhibits the opposite tendency under vertical strain. These findings provide a thorough understanding of Al1−xScxN ferroelectric alloys and a guideline for designing high-performance Al1−xScxN ferroelectric alloys. [ABSTRACT FROM AUTHOR]

We investigate the Sc dependence and thermal sensitivity of Al1−xScxN with the aid of Landau–Devonshire free energy recently proposed for its wurtzite ferroelectric phase. In particular, we calculate compositional and temperature dependences of the remanent polarization and the coercive field. Because the polarization is strong, surface fluctuations of the polarization are expected; we examine the nature of these fluctuations. Strong correlation is expected as the ferroelectric phase gives way to the paraelectric phase. [ABSTRACT FROM AUTHOR]

The research for wurtzite‐type ternary nitride semiconductors containing earth abundant elements with a stoichiometry of 1 : 1 : 2 was focused on metals like Mg or Zn, so far. The vast majority of these Grimm–Sommerfeld analogue compounds crystallize in the β‐NaFeO2 structure, although a second arrangement in space group Pmc21 is predicted to be a viable alternative. Despite extensive theoretical and experimental studies, this structure has so far remained undiscovered. Herein, we report on BeGeN2 in a Pmc21 structure, synthesized from Be3N2 and Ge3N4 using a high‐pressure high‐temperature approach at 6 GPa and 800 °C. The compound was characterized by powder X‐ray diffraction (PXRD), solid state nuclear magnetic resonance (NMR), Raman and energy dispersive X‐ray (EDX) spectroscopy, temperature‐dependent PXRD, second harmonic generation (SHG) and UV/Vis measurements and in addition also compared to its lighter homologue BeSiN2 in all mentioned analytic techniques. The synthesis and investigation of both the first beryllium germanium nitride and the first ternary wurtzite‐type nitride crystallizing in space group Pmc21 open the door to a new field of research on wurtzite‐type related structures. [ABSTRACT FROM AUTHOR]

Thin films of silver-doped zinc oxide (SZO) were deposited at room temperature using a DC reactive magnetron co-sputtering technique using two independent Zn and Ag targets. The crystallographic structure, chemical composition and surface morphology of SZO films with different silver concentrations were correlated with the photocatalytic (PC) properties. The crystallization of the SZO films was made using millisecond range flash-lamp-annealing (FLA) treatments. FLA induces significant structural ordering of the wurtzite structure and an in-depth redistribution of silver, resulting in the formation of silver agglomerates. The wurtzite ZnO structure is observed for silver contents below 10 at.% where Ag is partially incorporated into the oxide matrix, inducing a decrease in the optical band-gap. Regardless of the silver content, all the as-grown SZO films do not exhibit any significant PC activity. The best PC response is achieved for samples with a relatively low Ag content (2–5 at.%) after FLA treatment. The enhanced PC activity of SZO upon FLA can be attributed to structural ordering and the effective band-gap narrowing through the combination of silver doping and the plasmonic effect caused by the formation of Ag clusters. [ABSTRACT FROM AUTHOR]

Undoped ZnO and Mg-doped ZnO (ZnO:Mg) nanoparticles (NPs), with Mg concentration ranging from x = 1 to 5 at%, were synthesized by the sol–gel method. The magnesium content effects on the different ZnO:Mg NPs properties have been investigated by a variety of techniques. X-ray results showed that the prepared samples were crystalline with a hexagonal wurtzite phase. The structural study revealed that samples are assembled in nanostructures with average crystallite sizes ranging from 37 to 41 nm. The elemental analysis confirms the incorporation of the Mg ions into the ZnO matrix. The TEM images show the hexagonal shape and the nanometric size of undoped ZnO and ZnO:Mg NPs. The estimated bandgap energies of the ZnO:Mg samples were 3.20 eV, 2.86 eV, 2.77 eV, and 2.99 eV for x = 0, 1, 3, and 5 at%, respectively. The ethanol-sensing properties of ZnO:Mg(3%) NPs, prepared in the form of film, were investigated in the temperature range of 300–400 °C at different ethanol concentrations. The linear responses from ZnO and ZnO:Mg NPs-based sensors were detected at the working temperature of 400°C in the 30–50 ppm level range. The obtained results outline an enhancement in sensing performances for a ZnO:Mg(3%)-based sensor towards ethanol gas compared to those of a pure ZnO-based sensor. The sensors exhibited short response and rapid recovery times, 4 and 23 s, respectively, to ethanol gas. The high, reversible, and fast response of the ZnO:Mg(3%)-based sensor indicates its potential application as a gas sensor to detect ethanol. [ABSTRACT FROM AUTHOR]

Zn0.64Mg0.36O (ZMO) is a newly discovered ferroelectric oxide with the wurtzite structure. Epitaxial Zn0.64Mg0.36O films from 0.036 to 0.5 μm in thickness are grown on Pt/sapphire with the crystallographic c-axis out of plane. At room temperature, the remanent polarization is ∼80 μC/cm2 and the coercive field is ∼3 MV/cm. The coercive field is strongly temperature dependent up to 240 °C with a pseudo-activation energy of 23 ± 0.3 meV, suggesting that polarization reversal occurs through an extrinsic process such as domain wall motion. ZMO films can be woken up in 20 electric field cycles on driving near the coercive field; they wake up in a single loop at fields in excess of 4 MV/cm. A thermally activated fluid imprint process, with a pseudo-activation energy of 67 ± 8 meV, enlarges the coercive field by several hundred kV cm−1 after switching the polarization. Additionally, ZMO films exhibit excellent retention characteristics; no reduction in the polarization is observed up to 1000 h from room temperature to 200 °C bakes. This current early generation of ZMO films can survive several thousand switching cycles before dielectric breakdown occurs. [ABSTRACT FROM AUTHOR]

Local mapping of piezoelectric response across grains with different crystal planes is crucial to enhance the level of understanding of the piezoelectric behavior of wurtzite hexagonal (WH) AlN thin films. To investigate this phenomenon, polycrystalline WH-AlN thin films were deposited by pulsed-DC magnetron sputtering using a mixture of argon (Ar) and nitrogen (N2) with varying N2 content as 5%, 10%, and 20% in the form of the AlN/Ti/Si (100) heterostructure. Piezo force microscopy (PFM) was used to establish a correlation among piezo-response (PR) phase contrast, polarity, and crystal planes constituting the film surface. A phenomenological model is also presented to correlate the distribution of interface sheet charges with polar (0002)-, semi-polar (10 1 ¯ 1)-, and non-polar (10 1 ¯ 0)-planes present on the film surface. This interdependence eventually regulates the phase between piezoelectric oscillations and modulation voltage, which is ultimately translated into a grain-wise contrast obtained from PR-phase images. [ABSTRACT FROM AUTHOR]

Semiconductor nanoholes have garnered significant interest due to their unique nanotopological structures, which can result in distinct physicochemical characteristics. This study delves into the properties of crystal vibrations in nanohole structures. The analytic Fröhlich phonon state and dispersion relationship in wurtzite nanoholes, with circular and square cross sections (CS), are derived using the macroscopic dielectric continuum model. It is found that two types of phonon modes, surface optical (SO) and half‐space (HS) modes, coexist in wurtzite nitride nanohole structures. These phonon modes and their dispersive behaviors in nanoholes significantly differ from those in nanowires due to the different nanotopological structures. Furthermore, the Fröhlich electron–phonon interaction Hamiltonians for SO and HS phonon modes in nanoholes are obtained based on a field quantization scheme. Numerical calculations on wurtzite AlN nanoholes reveal that the shape of the CS has a remarkable influence on the dispersive spectra of SO and HS phonon modes. Additionally, it is found that the dielectric medium significantly affects the dispersive features of SO modes, while its influence on the dispersive behavior of HS modes is negligible. The profound physical mechanisms behind these observations are deeply analyzed. [ABSTRACT FROM AUTHOR]

A study on the formation of InGaN ternary compounds in the three-dimensional growth mode is presented. For the first time, we demonstrate that the self-organization during InGaN growth is responsible for the formation of core–shell nanowires (NWs), nanotubes, zinc blende (ZB) phases, and nanoflowers. It is found that the core–shell InGaN NWs are formed at the very initial stage of growth. An increase in growth time results in the ascending indium diffusion from the cores of NWs and their accumulation at the NW tips, enabling three-dimensional lateral growth and formation of nanotubes. Further nanostructure growth leads to the formation of nanoflowers with empty stems and ZB/wurtzite (WZ) phase interface at the periphery. The observed structural transformations of NWs are supported by transmission electron microscopy and photoluminescence measurements, as well as theoretical estimates. Understanding the formation mechanisms of these complex three-dimensional nanostructures can facilitate the development of InGaN compounds for gas-sensing applications. [ABSTRACT FROM AUTHOR]

Hematite α-Fe 2 O 3 exhibits a slow catalytic reaction rate and low performance in aqueous pollutant decomposition. In this work, α-Fe 2 O 3 /CdS binary heterostructure composites were created by introducing different ratios of wurtzite CdS into α-Fe 2 O 3 within 0–100 wt% via precipitation and impregnation methods. The photocatalytic performance of α-Fe 2 O 3 /CdS was enhanced for the decomposition of aqueous rhodamine 6G (R6G) dye under ultraviolet (UV) irradiation. SEM images reveal that higher CdS loading results in increased interfacial contact between rod-like CdS and spherical-shaped α-Fe 2 O 3. XRD and FTIR results confirm the coexistence of rhombohedral α-Fe 2 O 3 and hexagonal CdS phases, with peak strength proportional to the ratio of component loading, as the respective elements were verified through EDX analysis. The UV-Vis spectroscopic analysis exhibits an enhancement in optical absorption and band gap broadening as the CdS loading rises. α-Fe 2 O 3 /CdS with increased CdS loading exhibits faster and more efficient R6G degradation under UV exposure, as evidenced by greater rate constants and degradation efficiency, with optimal CdS loading of 90 wt% achieving a maximum efficiency of 79.14%. The present heterostructure could be employed in future wastewater remediation for effective removal of organic dye pollutants, further promoting clean water preservation for global environmental sustainability. [ABSTRACT FROM AUTHOR]

This research article presents a comprehensive first-principles study on the piezoelectric properties of Wurtzite Aluminum Nitride (AlN) films under in-plane strain conditions. By calculating the piezoelectric tensor coefficients (e33, e31, and e15), we investigate the variation patterns of these constants with respect to in-plane strain. Our results indicate significant changes in the piezoelectric constants within the range of in-plane strain considered, exhibiting a linear trend despite opposite trends for e33 compared to e31 and e15. This study highlights the extreme sensitivity of AlN films' piezoelectric performance to in-plane strain, suggesting its potential as an effective means for tuning and optimizing the piezoelectric properties of AlN-based devices. [ABSTRACT FROM AUTHOR]

Spin-polarized photoemission from wurtzite and zinc blende gallium nitride (GaN) photocathodes has been observed and measured. The p-doped GaN photocathodes were epitaxially grown and activated to negative electron affinity with a cesium monolayer deposited on their surfaces. A field-retarding Mott polarimeter was used to measure the spin polarization of electrons photoemitted from the top of the valence band. A spectral scan with a tunable optical parametric amplifier constructed to provide low-bandwidth light revealed peak spin polarizations of 17% and 29% in the wurtzite and zinc blende photocathodes, respectively. Zinc blende GaN results are analyzed with a spin polarization model accounting for experimental parameters used in the measurements, while possible mechanisms influencing the obtained spin polarization values of wurtzite GaN are discussed. [ABSTRACT FROM AUTHOR]

The present research describes the optical, structural, dielectric, photocatalytic, and antibacterial characteristics of potassium‐doped ZnO thin films synthesized via sol–gel dip coating technique with a K doping concentration of (1, 2, 3, 4, 5) wt%. Thin films are annealed at optimized temperatures. K‐doped ZnO has a hexagonal wurtzite phase having a preferential orientation along the (101) plane. The size of the crystallite decreases as the potassium doping percentage rises. Optical analysis reveals that the bandgap decreases when the quantity of K doping in ZnO increases. Dielectric constant experiments show that when the K doping % is raised, AC conductivity of thin films rises as well. Thin film resistivity and Hall coefficient decrease with increasing K concentration, but conductivity, mobility, and carrier concentration rise. Gram‐positive and gram‐negative bacteria are both responsive to K‐doped ZnO. With such antibacterial properties, K‐doped ZnO can be used in biomedicine and to protect the environment. The methylene blue dye is effectively degraded by the photocatalyst K‐doped ZnO, making it useful for removing pollution from wastewater. [ABSTRACT FROM AUTHOR]

III-nitrides and related alloys are widely used for optoelectronics and as acoustic resonators. Ferroelectric wurtzite nitrides are of particular interest because of their potential for direct integration with Si and wide bandgap semiconductors and unique polarization switching characteristics; such interest has taken off since the first report of ferroelectric Al1−xScxN alloys. However, the coercive fields needed to switch polarization are on the order of MV/cm, which are 1–2 orders of magnitude larger than oxide perovskite ferroelectrics. Atomic-scale point defects are known to impact the dielectric properties, including breakdown fields and leakage currents, as well as ferroelectric switching. However, very little is known about the native defects and impurities in Al1−xScxN and their effect on the dielectric and ferroelectric properties. In this study, we use first-principles calculations to determine the formation energetics of native defects and unintentional oxygen incorporation and their effects on the polarization switching barriers in Al1−xScxN alloys. We find that nitrogen vacancies are the dominant native defects, and unintentional oxygen incorporation on the nitrogen site is present in high concentrations. They introduce multiple mid-gap states that can lead to premature dielectric breakdown and increased temperature-activated leakage currents in ferroelectrics. We also find that nitrogen vacancy and substitutional oxygen reduce the switching barrier in Al1−xScxN at low Sc compositions. The effect is minimal or even negative (increases barrier) at higher Sc compositions. Unintentional defects are generally considered to adversely affect ferroelectric properties, but our findings reveal that controlled introduction of point defects by tuning synthesis conditions can instead benefit polarization switching in ferroelectric Al1−xScxN at certain compositions. [ABSTRACT FROM AUTHOR]

Photoanodes possessing multifunctionality for efficient clean fuel generation have garnered significant attention. In this study, we present successful fabrication of tungsten‐doped ZnO photoelectrodes, resulting in enhanced photoelectrochemical water‐splitting performance. A single‐step deposition process was employed to achieve thin films with excellent adhesion on FTO substrates, eliminating the need for post‐annealing treatments. The addition of tungsten into the ZnO matrix extended the optical absorbance range of the thin films to the visible spectrum, leading to improved photoelectrochemical performance under visible light irradiation. At an applied potential of 0.85 V vs. RHE, the as‐fabricated tungsten‐doped ZnO thin films exhibited a remarkable photocurrent density of 5218 μA/cm2, which was eight times higher than that of the undoped ZnO electrode. The incorporation of tungsten in the ZnO photoanode resulted in increased charge carrier density and enhanced visible light absorption, consequently elevating the photocurrent density. [ABSTRACT FROM AUTHOR]

Lattice‐asymmetry‐driven selective area sublimation (SAS) process of GaN is systemically investigated by exploring the in situ dynamic evolution of the decomposition pathway under ultra‐high vacuum. The rationale of the SAS is confirmed as a strong anisotropic decomposition driven by lattice‐asymmetry of wurtzite crystal: the sublimation preferably starts along the ‐c axis due to the relatively lower decomposition energy barrier. Finally, the fabrication of site‐ and size‐controlled GaN nanowires has been achieved by utilizing the SAS process, exhibiting good controllability on the sidewall of nanowires. These findings shed light on the thermodynamic mechanism of the lattice‐asymmetry‐driven sublimation process in III‐nitrides, providing an efficient alternative approach for the tailoring of semiconductor micro/nanostructures. [ABSTRACT FROM AUTHOR]

In this work, the Co doped ZnO (CZO) hierarchical structures were synthesized via hydrothermal approach at 100 °C. The results of characterization illustrated that the products were assembled by large quantities of ultra-thin nanosheets with porous feature, the average crystallite size decreased from 20.27 nm to 16.98 nm with doping, and Co element existed uniformly in the hexagonal wurtzite ZnO lattice in the form of coexisting Co2+/Co3+ ions and did not appear as secondary phases. Triethylamine (TEA) sensing performance of the CZO sensor were investigated in the concentration range of 2–100 ppm, it possessed ameliorative and potential sensing characteristics, such as enhanced response value (24) doubled as compared to ZnO (12), higher selectivity coefficient (> 2.18), and shorter response and recovery time (7 s/44 s) in the case of 50 ppm TEA, and relatively well repeatability and stability no less than 40 days at 270 °C. The enhanced TEA sensing performance principally put down to the synergistic influence of the catalytic effect of Co element and the increased number of oxygen vacancy and adsorbed oxygen by introducing Co ions. [ABSTRACT FROM AUTHOR]

Context: The present study reports the properties of pressure-induced phase transition, electronic and optical of phosphides XSiP2 under pressure in chalcopyrite, sodium chloride (rock salt), and Wurtzite phases. The study shows the chalcopyrite phase as the most stable phase among the other studied phases. The obtained structural parameters in the chalcopyrite and rock-salt phases reasonably agree with the literature. The computed band structures revealed a semiconductor behavior in chalcopyrite structure and metallic behavior for rock- salt and wurtzite structures. In the energy range of 0 to 30 eV, optical parameters such as the real and imaginary parts of the dielectric constant, refractive index, and reflectivity are calculated and compared with existing data. Our optical properties findings are predictive for the rock-salt and wurtzite phases. Since no results are available in the literature, these results may serve as references for other theoretical and experimental studies. Method: The calculations are performed by employing the "full-potential linearized augmented plane wave (FP-LAPW) method within density functional theory (DFT)." [ABSTRACT FROM AUTHOR]

Polarization arising from non-centrosymmetric wurtzite lattice underpins the physics and functionality of gallium nitride (GaN)—the most produced semiconductor materials second only to silicon. However, recent direct experimental measurements unveiled remanent polarization of unexpectedly large magnitudes and opposite orientations to traditionally anticipated. This significant discrepancy not only poses a formidable challenge to our existing theoretical paradigms but also accentuates the need for a critical rethinking and methodological refinement to integrate these emerging observations with established knowledge, mitigating potential misunderstandings and misconceptions in this rapidly evolving field. [ABSTRACT FROM AUTHOR]

It is well known that hexagonal Ge has a direct bandgap and exhibits excellent light emission. The structure and electrical characteristics of hex-GeSn alloys are investigated using an ab initio computation and the PBEsol-meta-GGA-mBJ function. In all alloys, the direct bandgap is observed. Due to the high radius of the Sn atom, when Sn content increases, the bandgap decreases and lattice parameters expand. Their spin–orbit, crystal field splitting and effective mass of electron and hole were also determined, indicating that the direct bandgap of hex-GeSn alloys has significant application in optoelectronic. [ABSTRACT FROM AUTHOR]

The surface frustrated Lewis pairs (SFLPs) open up new opportunities for substituting noble metals in the activation and conversion of stable molecules. However, the applications of SFLPs on a larger scale are impeded by the complex construction process, low surface density, and sensitivity to the reaction environment. Herein, wurtzite‐structured crystals such as GaN, ZnO, and AlP are found for developing natural, dense, and stable SFLPs. It is revealed that the SFLPs can naturally exist on the (100) and (110) surfaces of wurtzite‐structured crystals. All the surface cations and anions serve as the Lewis acid and Lewis base in SFLPs, respectively, contributing to the surface density of SFLPs as high as 7.26×1014 cm−2. Ab initio molecular dynamics simulations indicate that the SFLPs can keep stable under high temperatures and the reaction atmospheres of CO and H2O. Moreover, outstanding performance for activating the given small molecules is achieved on these natural SFLPs, which originates from the optimal orbital overlap between SFLPs and small molecules. Overall, these findings not only provide a simple method to obtain dense and stable SFLPs but also unfold the nature of SFLPs toward the facile activation of small molecules. [ABSTRACT FROM AUTHOR]

Ferroelectric, phase-change, and magnetic materials are considered promising candidates for advanced memory devices. Under the development dilemma of traditional silicon-based memory devices, ferroelectric materials stand out due to their unique polarization properties and diverse manufacturing techniques. On the occasion of the 100th anniversary of the birth of ferroelectricity, scandium-doped aluminum nitride, which is a different wurtzite structure, was reported to be ferroelectric with a larger coercive, remanent polarization, curie temperature, and a more stable ferroelectric phase. The inherent advantages have attracted widespread attention, promising better performance when used as data storage materials and better meeting the needs of the development of the information age. In this paper, we start from the characteristics and development history of ferroelectric materials, mainly focusing on the characteristics, preparation, and applications in memory devices of ferroelectric wurtzite AlScN. It compares and analyzes the unique advantages of AlScN-based memory devices, aiming to lay a theoretical foundation for the development of advanced memory devices in the future. [ABSTRACT FROM AUTHOR]

This study explores the synthesis of nanoparticles through the thermal decomposition of single‐source precursors, a method gaining popularity due to its low cost, minimal environmental toxicity, rapidity, scalability, and the ability to form nanoparticles with few defects. Zinc ethyl carbamate was synthesized and characterized using 1H NMR and infrared spectroscopy. Its purity was confirmed through microelemental analysis and melting point determination. The melting point of the complex was determined to be 165 °C. The thermogravimetric analyses indicated a one‐step decomposition of zinc ethyl carbamate with a decomposition onset of of 200 °C, yielding a stable ZnS residue. Further thermal decomposition led to the formation of wurtzite phase ZnS nanoparticles, as evidenced by XRD. SEM micrographs displayed mixed spherical, and cubic unevenly sized, polydispersed nanoparticles, while EDX revealed approximately a 1 : 1 Zn to S ratio. Estimated band gap from the Tauc's plot gave 3.93 eV and 3.42 eV for the nanoparticles synthesized at 300 and 400 °C respectively. The wide difference in the band gaps may be as a result of the larger particles observed at 400 °C and the deformations in the sample as observed in the SEM. [ABSTRACT FROM AUTHOR]

Debye–Callaway model in combination with the Murnaghan and Clapeyron equations was used to calculate the hydrostatic pressure effects on lattice thermal conductivity (LTC) of wurtzite gallium nitride. The calculations are for the longitudinal and transverse phonon modes. The results are efficiently fitted with the whole temperature (1–400) of the experimental data. The peak value of LTC declines with the applied pressure from 0 to 14 GPa. This result is due to the decreasing Debye temperature, group velocity and lattice volume. Furthermore, pressure affected the number of dislocations, sample size and Gruneisen parameter (longitudinal and transverse) modes. Consequently, the values of above parameters at zero GPa are 2.5 × 10 13 m - 2 , 1.8 mm , 0.93 and 0.52 , whilst the values at 14 GPa are 15 × 10 15 m - 2 , 1.68 mm , 0.818 and 0.469 , respectively. The results show that hydrostatic pressure does not affect the number of impurities and electron concentrations. [ABSTRACT FROM AUTHOR]

p-type Ag-N dual acceptor doped ZnO thin films with long electrical stability were deposited by DC magnetron reactive co-sputtering technique. After deposition, the films were annealed at 400 °C for one hour in a nitrogen-controlled atmosphere. The deposited films were amorphous. However, after annealing, they crystallize in the typical hexagonal wurtzite structure of ZnO. The Ag-N dual acceptors were incorporated substitutionally in the structure of zinc oxide, and achieving that; the three samples presented the p-type conductivity in the ZnO. Initial electrical properties showed a low resistivity of from 1 to 10−3 Ω·cm, Hall mobility of tens cm2/V·s, and a hole concentration from 1017 to 1019 cm−3. The electrical stability analysis reveals that the p-type conductivity of the ZnO:Ag,N films is very stable and does not revert to n-type, even after 36 months of aging. These results reveal the feasibility of using these films for applications in short-wavelength or transparent optoelectronic devices. [ABSTRACT FROM AUTHOR]

MgZnO barriers are commonly applied to passivate wurtzite ZnO films to enhance electron mobility, while the Mg mole fraction x is usually controlled below 0.4 to avoid phase separation. Few theoretical analyses have focused on electron mobility at large x since the phase separation leads to a complex scattering mechanism. This work investigates the effects of asymmetric MgZnO barriers on electron mobility, which is one source of complexity. Four asymmetric quantum wells simultaneously contribute to the electron mobility in proportions when the wurtzite and rock salt coexist in the mixed-phase MgZnO barriers with large Mg mole fractions. Besides, built-in electric fields also contribute to the asymmetry by tilting the bands. The polar optical phonon-limited electron mobility in asymmetric MgxZn1−xO/ZnO/Mg0.45Zn0.55O quantum wells is simulated between 176 and 333 cm2/V s as x ranges from 0.1 to 1. Our calculations show that confined optical phonons play a leading role in the quantum well with wurtzite barriers. Interface optical phonons are primary in the wells with rock salt barriers since most electrons are pushed close to the interface by the strong built-in electric field. The results indicate that wurtzite barriers are more favorable to achieving stable high mobility above 238 cm2/V s as the Mg mole fraction ranges from 0.14 to 0.33, which is commonly applied in practice. [ABSTRACT FROM AUTHOR]

The properties of most III–V semiconductor materials in the wurtzite structure are not known because of their metastable character. However, recent advances in the growth of III–V wurtzite nanorods open new perspectives for applications. In this work, we present a systematic computational study of bulk wurtzite III–V semiconductors, using predictive ab initio methods, to provide a necessary base knowledge for studying the nanostructures. The most important physical properties of bulk systems, i.e., lattice constants, elasticity, spontaneous polarization, piezoelectricity, band structures, deformation potentials, and band offsets, have been studied. Comparison with the available experimental and theoretical data shows the high credibility of our results. Moreover, we provide a complete set of parameters for a six-band k ⋅ p model, which is widely used for simulating devices based on semiconductor heterostructures. [ABSTRACT FROM AUTHOR]

The structural, elastic, and basic thermodynamic properties of hexagonal ScxAl1−xN crystals are calculated and discussed over the whole range of possible random alloys, including the transition from wurtzite to the layered hexagonal structure. Based on a review of lattice and internal parameters in combination with complete datasets of stiffness coefficients published in the literature, differing in the considered alloying intervals and the predicted structural transitions, changes in the crystal lattices caused by the substitution of aluminum by scandium atoms are discussed and illustrated. Crystal properties like the mass densities, average bond angles, and bond lengths are calculated, and the compliance coefficients, Young's modulus, shear modulus, Poisson's ratio, compressibility, and sound velocities are determined depending on the alloy composition and in relation to the orientation of crystal planes and axes. Particular attention is paid to the occurring directional anisotropies and the changes in structural and elastic properties in the alloy region of the structural transition between wurtzite and layered hexagonal ScxAl1−xN crystals. The acoustic velocities determined are used to calculate basic thermodynamic properties such as the Debye temperature, heat capacity, and minimum heat conduction, as well as to evaluate both the influence of the alloying and the structural transition on these properties. [ABSTRACT FROM AUTHOR]

Growth of wurtzite ScxAl1−xN (x < 0.23) by plasma-assisted molecular-beam epitaxy on c-plane GaN at high temperatures significantly alters the extracted lattice constants of the material due to defects likely associated with remnant phases. In contrast, ScAlN grown below a composition-dependent threshold temperature exhibits uniform alloy distribution, reduced defect density, and atomic-step surface morphology. The c-plane lattice constant of this low-temperature ScAlN varies with composition as expected from previous theoretical calculations and can be used to reliably estimate alloy composition. Moreover, lattice-matched Sc0.18Al0.82N/GaN multi-quantum wells grown under these conditions display strong and narrow near-infrared intersubband absorption lines that confirm advantageous optical and electronic properties. [ABSTRACT FROM AUTHOR]

ZnO and Zn(0.97-x)Al0.03MnxO (x = 0.00 (AlMnZ0), 0.04 (AlMnZ4), 0.05 (AlMnZ5) and 0.06 (AlMnZ6)) nanopowders that have been synthesized in powder form by using coprecipitation method at powder-based low temperature are zinc chloride (Sigma Aldrich), manganese (II) chloride tetrahydrate (Sigma Aldrich), and aluminum chloride hexahydrate (Sigma Aldrich). The powder of zinc chloride, aluminum chloride hexahydrate and manganese (II) chloride are dissolved in 0.5 M HCl, then a precipitating agent is added in the form of NaOH 5 M base into the solution by slowly dropping NaOH 5 M solution into the precursor until a pH of 10 is reached which causes the clear and transparent solution turns into milky white. In order for the reaction to run perfectly, the stirring process is carried out in a hot plate stirrer for 90 minutes at a temperature of 85 °C. After the solution is formed, it is washed with distilled water repeatedly until there is no impurities and it is filtered with filter paper to separate the precipitate from the solution. X-ray Diffraction (XRD) and Ultra Violet Visible (UV-VIS) Spectroscopy have been used to characterize ZnO nanopowder products through (Al+Mn) doping. The results show that AlMnZ0, AlMnZ4, AlMnz5 and AlMnZ6 nanopowder has the form of a hexagonal wurtzite crystal phase with a crystal size of ~38.03881-47.57561 nm. The optical band gap of ZnO nanopowder can be increased by atomic doping (Al+Mn). The increase in the optical band gap of AlMnZ0, AlMnZ4, AlMnZ5 and AlMnZ6 nanopowder is related to the Burstein-Moss effect, that is when (Al+Mn) atoms are successfully incorporated into ZnO nanopowders, there is a vacancy of the oxygen atom in the host crystal. [ABSTRACT FROM AUTHOR]

Due to the wide band gap of pure wurtzite ZnO, most of the visible light was not be absorbed, four kinds of K-doped ZnO supercell models were constructed by using the first principles based on density functional theory, and four models are geometrically optimized, and then the energy band structure, density of states and light absorption performance of KXZn1-XO are calculated. The results show that the band gap of pure zinc oxide calculated by general gradient approximation (GGA)+U method is 3. 373 eV, which is consistent with the experimental value. With the increase of K doping concentration X, the band gap of ZnO firstly increases, then decreases and finally increases. The absorption edge band of KXZn1-XO shifts blue firstly and then red. [ABSTRACT FROM AUTHOR]

The two-dimensional electron gas (2DEG) that forms on a semiconductor surface can be used to explore a variety of phenomena in quantum physics and plays an important role in nanoscale electronics, such as transistors. Controlling its formation is, thus, relevant. Using angle-resolved photoemission spectroscopy (ARPES) and accumulating the signal over many nanocrystals, we find that on clean InAs nanosheets with non-polar surfaces and wurtzite (WZ) crystal structures, a 2DEG can be observed at the Γ-point. We suggest that the step morphology on the WZ InAs specimens facilitates the appearance of the electron gas, since previous studies on InAs nanowire surfaces with the same crystal facet and a similar defect density did not exhibit a 2DEG. Subsequently, bismuth deposition leads to the disappearance of the 2DEG as well as a shift of the valence band. This is in contrast to previous observations on InAs surfaces, in which metal deposition would lead to the formation of a 2DEG. The control of the 2DEG with the addition of Bi atoms is relevant for applications of InAs nanosheets in quantum technologies. This study also illustrates that ARPES accumulated over several 2D materials oriented randomly around their normal axis can provide valuable information on their band structure with a fast turnover and low irradiation. [ABSTRACT FROM AUTHOR]

This theoretical study focuses on the performance of the surface plasmon resonance (SPR) sensor by strategically including various heterostructures in between the plasmonic metal and sensing medium. The heterostructure consists of a wurtzite nitride semiconductor and a two-dimensional (2D) material, specifically transition-metal dichalcogenides (TMDC). The angular interrogation approach is used to assess the sensor's efficacy which includes all commonly used critical parameters. The study also outlines the range of refractive indices (RI) in the sensing medium that elicit exceptional and notable responses from the proposed SPR structure. Based on the sensitivity, detection accuracy (DA), and figure of merit (FOM) values, it is determined that a TMDC material, specifically tungsten disulfide (WS2), combined with a wurtzite nitride semiconductor (such as gallium nitride, indium nitride, or aluminum nitride), offers the best performance. Among all heterostructures, GaN-WS2 exhibits the highest sensitivity. In contrast, AlN-WS2 exhibits remarkable performance in terms of DA, FOM, and the evanescent field intensity factor. Furthermore, the proposed SPR structure with InN-WS2 demonstrates maximum shifts in resonance angle, occurring within sensing RI range of 1.372 to 1.389. Similarly, AlN-WS2 exhibits the maximum shifts in resonance angle within the range from 1.387 to 1.4. GaN-WS2, however, shows the strongest response to resonance angle shifts within the range from 1.38 to 1.396. [ABSTRACT FROM AUTHOR]

The results of studies of the influence of Y as a reactive element on the properties of TiAlN coatings obtained by the method of vacuum-arc deposition are given. Changes in the structure and properties were analyzed using SEM in combination with EDX, XRD, indentation analysis and wear analysis. It is shown that the presence of Y changes the crystalline phase of the Ti0.6Al0.34Y0.06N coating. It consists of a combination of a cubic NaCl structure (basic phase) and a wurtzite structure (additional phase). In addition, it leads to a small grain size (12 nm) and a nano-columnar structure. The high hardness is partly the result of solution hardening due to the inclusion of larger Y atoms in the TiAlN lattice at the locations of the metal atoms. The reduced grain size of 12 nm also helps to increase the hardness of the coating. The hardness is 31 ± 2.5 GPa, the modulus of elasticity is 394.8 ± 35.8 GPa. The residual stress is approximately three times (-3352 ± 64 MPa) higher than the TiAlN coating (-720 MPa). In addition, a high level of compressive stress contributes to an increase in hardness, since defects responsible for their own compressive stress are an obstacle to dislocation movement. The improved hardness of the experimental coating can be explained by a triple effect: solution strengthening, grain grinding and high residual compressive stress. The addition of Y indicates a slower growth of the oxide layer on the surface of the coating during the wear test. After the addition of Y, Y ions preferentially separate at the grain boundaries and therefore effectively delay the inward diffusion of oxygen. The addition of Y promotes the formation of dense Al2O3, which is effective in restraining diffusion and therefore protects the coating from oxidative wear. [ABSTRACT FROM AUTHOR]

Spectroelectrochemical methods are employed to systematically investigate the impacts of external charge filling in three pure wurtzite CdSe/CdS core/shell nanocrystals (NCs) with different shell thicknesses. We observed that electrons can penetrate the thick CdS shell and inject into the conduction band with an abnormal brightening, while holes are blocked. The formed negative trions result in a different spectral shift according to the size of the NCs, with a redshift of 3.7 nm for 12.5 nm NCs and almost no movement for 23.4 nm NCs. Meanwhile, due to the formation of biexcitons, a variational spectral blueshift with the NCs' size can be determined in time-resolved photoluminescence spectroscopy. This indicates that the binding energy of both biexcitons and negatively charged excitons can be regulated by controlling the shell thickness. Extra charges can also be used to activate/passivate trap states, thereby confirming that the 12.5 nm sample has better surface/interface quality. [ABSTRACT FROM AUTHOR]

Consequences of incorporation of magnesium atom(s) on structural and optoelectronic properties of wurtzite cadmium sulphide have been investigated from first-principle calculations. Like direct (Γ–Γ) band-gap end binary wurtzite cadmium and magnesium sulphide semiconductors, such incorporation also results in stable direct (Γ–Γ) band-gap wurtzite MgxCd1−xS semiconductor ternary alloys with band-gaps residing in the UV spectral region. Lattice constants (a0, c0) of specimens within the w-MgxCd1−xS system nonlinearly reduce, while fundamental band-gap (Eg) enhances with increasing Mg content. Optical characteristics of optically anisotropic wurtzite crystals are studied mainly with ordinary and extraordinary components of real and imaginary parts of the complex dielectric function and some other dependent optical parameters. Electronic transitions from valence S-3p to Mg-4s, Mg-4p, Cd-5s and Cd-4p states of conduction band jointly result in optical features of the ternary alloys. Each uniaxial wurtzite crystal shows birefringence. Optical energy gap (Eopt) of each ternary alloy, higher than the corresponding Eg, lies in the UV region. Calculated components of static optical constants for ternary alloys become lower, but critical point energies become higher for larger band-gap specimen and vice versa. High optical absorption of direct band-gap ternary alloys in the UV region leads them as a compatible semiconductor for fabricating faster UV optoelectronic devices with high efficiency. [ABSTRACT FROM AUTHOR]

Abstract This study explores the synthesis of nanoparticles through the thermal decomposition of single‐source precursors, a method gaining popularity due to its low cost, minimal environmental toxicity, rapidity, scalability, and the ability to form nanoparticles with few defects. Zinc ethyl carbamate was synthesized and characterized using 1H NMR and infrared spectroscopy. Its purity was confirmed through microelemental analysis and melting point determination. The melting point of the complex was determined to be 165 °C. The thermogravimetric analyses indicated a one‐step decomposition of zinc ethyl carbamate with a decomposition onset of of 200 °C, yielding a stable ZnS residue. Further thermal decomposition led to the formation of wurtzite phase ZnS nanoparticles, as evidenced by XRD. SEM micrographs displayed mixed spherical, and cubic unevenly sized, polydispersed nanoparticles, while EDX revealed approximately a 1 : 1 Zn to S ratio. Estimated band gap from the Tauc's plot gave 3.93 eV and 3.42 eV for the nanoparticles synthesized at 300 and 400 °C respectively. The wide difference in the band gaps may be as a result of the larger particles observed at 400 °C and the deformations in the sample as observed in the SEM.