The metalorganic chemical vapor deposition (MOCVD) dynamics of beta-gallium oxide (beta-Ga2O3) growth using trimethylgallium (TMGa) and oxygen as precursors were investigated through both theoretical thermodynamic analysis and experimental validation in a horizontal low-pressure hot-wall reactor. Thermodynamic analysis revealed that high-purity beta-Ga2O3 can be grown through the complete combustion of TMG-derived gallium and hydrocarbons. Furthermore, the complete combustion of intentionally supplied hydrogen into the growth system also prevents the degradation of beta-Ga2O3 growth. Therefore, a high input VI/III ratio that ensures full combustion of gaseous species in the growth system is preferred for beta-Ga2O3 MOCVD. The growth experiments were performed on 2-in. sapphire substrates under an input VI/III ratio of 250. beta-Ga2O3 growth was confirmed at growth temperatures between 740 and 950 degrees C, with the growth rate decreasing from 0.7 to 0.5 mu m/h as temperature increased. Thermodynamic analysis successfully reproduced this growth behavior under the effective VI/III ratio of 6.5. The results demonstrate that beta-Ga2O3 MOCVD occurred under thermal equilibrium conditions and was thermodynamically controllable. (c) 2025 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license.

In this study, we employ first-principles calculations to explore the structural and electronic properties of monoclinic Al2O3/Ga2O3 superlattices with varied layer thickness and to perform a comparative analysis with (AlxGa1−x)2O3 alloys. Our investigation examines the lattice constants and electronic energy bandgaps of both the superlattice structures and alloys across different Al concentrations, shedding light on the intricate relationship between composition and electronic properties. The analysis on electronic properties reveals that as the number of Al2O3 monolayers in the Al2O3/Ga2O3 superlattice rises from 2 to 6 monolayers, the bandgap correspondingly expands from 5.29 to 6.43 eV. The band alignment between monoclinic Al2O3 and Ga2O3 exhibits a type-II band alignment. The conduction and valence band offsets between the bulk material and Al2O3/Ga2O3 superlattice varies with change in the number of Al2O3 monolayers. Our study gives a deeper insight into the properties of the Al2O3/Ga2O3 superlattice and suggests a solution to the Al-phase separation issue in (AlxGa1−x)2O3 alloys for advanced semiconductor device applications.

Applying thermal annealing to hydrothermal ZnO crystals an enhancement of exciton lifetime from 80 ps to 40 ns was achieved boosting PL quantum efficiency of the UV luminescence up to 70 %. The lifetime improvement is related to the reduced density of carrier traps by a few orders of magnitude as revealed by the reduction of the slow decay tail in pump probe decays coupled with weaker defects-related PL. The diffusion coefficient was determined to be 0.5 cm2/s, providing a large exciton diffusion length of 1.4 μm. The UV PL lifetime drop at the lowest exciton densities was explained by capture to traps. Release of holes from acceptor traps provided delayed exciton luminescence with ∼200 μs day time and 390 meV thermal activation energy. Pump-probe decays provided exciton absorption cross-section of 9 × 10−18 cm2 at 1550 nm wavelength and verified the PL decay times of excitons. Amplitudes and decay times of the microsecond slow decay tails have been correlated with the trap densities and their photoluminescence. A surface recombination velocity of 500 cm/s and the bimolecular free carrier recombination coefficient 0.7 × 10−11 cm3/s were calculated. Therefore, the properly annealed hydrothermally grown ZnO can be a viable and integral part of many functional devices as light-emitting diodes and lasers.

Monoclinic ,B-Ga2O3 films grown on c-plane sapphire have been shown to exhibit six (201)-oriented domains, which are equally spaced by rotation around the surface normal and equally sized by volume that render the film optical response effectively uniaxial. We derive and discuss an optical model suitable for ellipsometry data analysis of such films. We model mid- and far-infrared ellipsometry data from undoped and electrically insulating films with an effective uniaxial dielectric tensor based on projections of all phonon modes within the rotation domains parallel and perpendicular to the sample normal, i.e., to the reciprocal lattice vector g201. Two effective response functions are described by the model, and found sufficient to calculate ellipsometry data that best match measured ellipsometry data from a representative film. We propose to render either effective dielectric functions, or inverse effective dielectric functions, each separately for electric field directions parallel and perpendicular to g201, by sums of Lorentz oscillators, which permit determination of either sets of transverse optical phonon-mode parameters, or sets of longitudinal optical phonon-mode parameters, respectively. Transverse optical modes common to both dielectric functions can be traced back to single-crystal modes with Bu character, while modes with Au character appear only within the dielectric function for polarization perpendicular to the sample surface. The thereby obtained parameter sets reveal all phonon modes anticipated from averaging over the sixfoldrotation domains of single crystal ,B-Ga2O3, but with slightly shifted transverse optical, and completely different longitudinal optical phonon modes. Structural analysis of the film revealed virtually strain-free material. We suggest small crystal grains and high density of grain boundaries as a possible origin for the observed transverse optical phonon-frequency shifts with respect to bulk material. The differences in longitudinal optical modes here compared to the bulk are hypothesized to be caused by averaging of the electric-field-induced polarization over many long-range ordered rotation domains. Our model can be useful for future analysis of free charge-carrier properties using infrared ellipsometry on multiple domain

A new growth approach, based on the hot-wall metalorganic chemical vapor deposition concept, is developed for high-quality homoepitaxial growth of Si-doped single-crystalline β-Ga2O3 layers on (010)-oriented native substrates. Substrate annealing in argon atmosphere for 1 min at temperatures below 600 °C is proposed for the formation of epi-ready surfaces as a cost-effective alternative to the traditionally employed annealing process in oxygen-containing atmosphere with a time duration of 1 h at about 1000 °C. It is shown that the on-axis rocking curve widths exhibit anisotropic dependence on the azimuth angle with minima for in-plane direction parallel to the [001] and maximum for the [100] for both substrate and layer. The homoepitaxial layers are demonstrated to have excellent structural properties with a β-Ga2O3(020) rocking curve full-widths at half-maximum as low as 11 arc sec, which is lower than the corresponding one for the substrates (19 arc sec), even for highly Si-doped (low 1019 cm−3 range) layers. Furthermore, the structural anisotropy in the layer is substantially reduced with respect to the substrate. Very smooth surface morphology of the epilayers with a root mean square roughness value of 0.6 nm over a 5 × 5 μm2 area is achieved along with a high electron mobility of 69 cm2 V−1 s−1 at a free carrier concentration n=1.9×1019 cm−3. These values compare well with state-of-the-art parameters reported in the literature for β-Ga2O3(010) homoepitaxial layers with respective Si doping levels. Thermal conductivity of 17.4 Wm−1K−1 is determined along the [010] direction for the homoepitaxial layers at 300 K, which approaches the respective value of bulk crystal (20.6 Wm−1K−1). This result is explained by a weak boundary effect and a low dislocation density in the homoepitaxial layers.

In this work, we demonstrate the capability of the hot-wall metalorganic chemical vapor deposition to deliver high-quality n-Al ������Ga1-������N (x = 0 - 0.12, [Si] = 1 x 1017 cm-3) epitaxial layers on 4H-SiC(0001). All layers are crack-free, with a very small root mean square roughness (0.13 - 0.25 nm), homogeneous distribution of Al over film thickness and a very low unintentional incorporation of oxygen at the detection limit of 5 x 1015 cm-3 and carbon of 2 x 1016 cm-3. Edge type dislocations in the layers gradually increase with increasing Al content while screw dislocations only raise for x above 0.077. The room temperature electron mobility of the n-Al ������Ga1-������N remain in the range of 400 - 470 cm2/(V.s) for Al contents between 0.05 and 0.077 resulting in comparable or higher Baliga figure of merit with respect to GaN, and hence demonstrating their suitability for implementation as drift layers in power device applications. Further increase in Al content is found to result in significant deterioration of the electrical properties.

In this work, we demonstrate the capability of the hot-wall metalorganic chemical vapor deposition to deliver high-quality n-AlxGa1−xN (x = 0-0.12, [Si] = 1×1017 cm−3) epitaxial layers on 4H-SiC(0001). All layers are crack-free, with a very small root mean square roughness (0.13–0.25 nm), homogeneous distribution of Al over film thickness and a very low unintentional incorporation of Oxygen at the detection limit of 5×1015 cm−3 and Carbon of 2×1016 cm−3. Edge type dislocations in the layers gradually increase with increasing Al content while screw dislocations only raise for x above 0.077. The room temperature electron mobility of the n-AlxGa1−xN remain in the range of 400–470 cm2/V.s for Al contents between 0.05 and 0.077 resulting in comparable or higher Baliga figure of merit with respect to GaN, and hence demonstrating their sutability for implementation as drift layers in power device applications. Further increase in Al content is found to result in significant deterioration of the electrical properties.

Motivated by the successful synthesis of the porous graphitic carbon nitride (C6N7) monolayer very recently, we investigate the structural and electronic properties of C6N7 with doped and embedded with various atoms by means of spin-polarized density functional theory calculations. C6N7 monolayers doped with B, N, C, and O atoms have been revealed as stable and predicted to be feasible for experimental fabrication as free-standing monolayers based on the energy and thermal stability. Our computations demonstrate that while the C6N7 is a semiconductor, the doped C6N7 monolayers can be metal, dilute-magnetic semiconductor or half-metal. Further, a non magnetic moment is discovered in three of the doped C6N7 models and their electronic properties are disclosed to depend strongly on the spin configurations. The electronic properties of C6N7 depend on the doping atoms and doping sites. Furthermore, the effect of embedding of common nonmetal atoms such as B, C, N, S, O, Al, Si and P as well as transition metal including Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn atoms on the electronic and magnetic behavior of the C6N7 are studied. The charge transfer analysis shows that all embedded atoms act as electron donors, expect N, O and S atoms which act as electron acceptors when interacting with C6N7. The modification of the electronic band structure of C6N7 as the underlying mechanism for the changes in its electronic properties has been investigated. The intention is to demonstrate how entering the above mentioned impurities changes the nature of C6N7 into a metal, ferromagnetic-metal or dilute-magnetic semiconductor. These findings give not only an insight into the physical properties of doped and embedded C6N7 monolayer by different atoms, but also can serve as a guide to discover future possible applications of this novel material.

In this work, novel two-dimensional BC2X (X = N, P, As) monolayers with X atoms out of the B-C plane, are predicted by means of the density functional theory. The structural, electronic, optical, photocatalytic and thermoelectric properties of the BC2X monolayers have been investigated. Stability evaluation of the BC2X single-layers is carried out by phonon dispersion, ab-initio molecular dynamics (AIMD) simulation, elastic stability, and cohesive energies study. The mechanical properties reveal all monolayers considered are stable and have brittle nature. The band structure calculations using the HSE06 functional reveal that the BC2N, BC2P and BC2As are semiconducting monolayers with indirect bandgaps of 2.68 eV, 1.77 eV and 1.21 eV, respectively. The absorption spectra demonstrate large absorption coefficients of the BC2X monolayers in the ultraviolet range of electromagnetic spectrum. Furthermore, we disclose the BC2N and BC2P monolayers are potentially good candidates for photocatalytic water splitting. The electrical conductivity of BC2X is very small and slightly increases by raising the temperature. Electron doping may yield greater electric productivity of the studied monolayers than hole doping, as indicated by the larger power factor in the n-doped region compared to the p-type region. These results suggest that BC2X (X = N, P, As) monolayers represent a new promising class of 2DMs for electronic, optical and energy conversion systems.

Accumulation of ion-beam-induced structural disorder in wide bandgap semiconductors β-Ga2O3 and GaN irradiated at room temperature by 40 keV P ions has been studied by Rutherford backscattering/channeling spectrometry. Results show that despite the damage versus depth profiles are bimodal in both β-Ga2O3 and GaN, the kinetics of radiation damage accumulation is drastically different for these two materials. It is also demonstrated that β-Ga2O3 is more than one order less radiation resistant as compared to GaN for the irradiation conditions under consideration.

Density of collision cascades is one of the most important parameters determining defect formation in materials under ion bombardment. Here we study the role of the cascade density on the damage buildup in β-Ga2O3 using “molecular effect”, i.e. compare the damage formation under irradiations with monatomic (F, P) and small molecular (PF2) ions. Results show that a strong collision cascade density effect takes place in β-Ga2O3, so that molecular ions produce more damage both near the surface and in the region between surface and bulk defect peaks.

Recently, reported a comments on the our paper [JAP21-AR-03574R].. For clarification, we applied the fingerprint theory to examine the similarity between the distinct structures. The fingerprint function is a crystal structure descriptor, an 1D-function related to the pair correlation function and diffraction patterns. It does not depend on absolute atomic coordinates, but only on interatomic distances. Small deviations in atomic positions will influence the fingerprints only slightly [1-3]. Fingerprint theory allows quantification of the degree of order and complexity of a crystal structure.

A systematic investigation of the structural, mechanical, electronic, and optical properties of puckered penta-like PdPSeX (XO, S and Te) Janus monolayers has been performed by means of the plane wave density functional theory. It is confirmed that the pentagonal PdPSeX monolayers are dynamically and mechanical stable by means of analysis of their phonon dispersion curves and the Born condition under harmonic approximation, respectively. The PdPSeX Janus monolayers are disclosed as brittle two-dimensional materials (2DMs). The PBE (HSE06)-based calculations exhibit they are indirect semiconductors with bandgap values of 0.65 (1.44) eV, 1.20 (2.02) eV, and 0.98 (1.70) eV for PbPSeO, PbPSeS, and PbPSeTe monolayer, sequentially. The computational results demonstrate the PdPSeTe monolayer as the best suited candidate for visible light absorption and photocatalytic water splitting within the considered pentagonal PdPSeX monolayers. Our ab-initio-based outcomes provide an insight into the fundamental properties of the penta-like PdPSeX Janus structures and surely would motivate further experimental and theoretical studies to reveal the full application potential of this new type of 2DMs.

Motivated by the large scienti c interest in development of double cation dopingof SrTiO3 (STO) within the last years aiming to improve the water-splitting activity,electronic and ionic conductivity of STO, we study the e ect of (La, X) and (Y, M)codoping (X=Al/Sc/Cr/Mn/Fe/Co/Ni/Mo, and M=Al/Cr/Mo) on the structure, elec-tronic, magnetic, optical and photocatalytic properties (for water-splitting and CO2reduction) of STO using spin-polarized hybrid density functional theory. In most considered cases, the X and M monodoping reduces the bandgap of STO more than the (La, X) and (Y, M) codoping except for the case of (La, Ni) codoping. Our results are in good agreement with the available experimental results. We found out La-/Y-doping, and (La/Y, Al)-/(La, Sc)-codoping can not improve the conductivity of STO, while other monodopants and codopants can increase it. The best suited candidates for mono-/co-doped STO-based photocatalysts are Fe-/(La, Ni)-STO. Furthermore, Fe-/Mn-/(La, Mn/Fe/Ni)-STO could be appropriate for spintronic applications.

The hot-wall metalorganic chemical vapor deposition (MOCVD) concept, previously shown to enable superior material quality and high performance devices based on wide bandgap semiconductors, such as Ga(Al)N and SiC, has been applied to the epitaxial growth of β-Ga2O3. Epitaxial β-Ga2O3 layers at high growth rates (above 1 μm/h), at low reagent flows, and at reduced growth temperatures (740 °C) are demonstrated. A high crystalline quality epitaxial material on a c-plane sapphire substrate is attained as corroborated by a combination of x-ray diffraction, high-resolution scanning transmission electron microscopy, and spectroscopic ellipsometry measurements. The hot-wall MOCVD process is transferred to homoepitaxy, and single-crystalline homoepitaxial β-Ga2O3 layers are demonstrated with a 2̄01 rocking curve width of 118 arc sec, which is comparable to those of the edge-defined film-fed grown (2̄01) β-Ga2O3 substrates, indicative of similar dislocation densities for epilayers and substrates. Hence, hot-wall MOCVD is proposed as a prospective growth method to be further explored for the fabrication of β-Ga2O3.

In this paper, the existence of monolayers with the chemical formula XO2, where X = Zn, Cd, and Hg with hexagonal and tetragonal lattice structures is theoretically predicted by means of first principles calculations.

Structural, electronic, optic and vibrational properties of Zinc antimonide (ZnSb) monolayers and their functionalized (semi-fluorinated and fully chlorinated) structures are investigated by means of the first-principles calculations. The phonon dispersion curves reveal the presence of imaginary frequencies and thus confirm the dynamical instability of ZnSb monolayer. The calculated electronic band structure corroborates the metallic character with fully-relativistic calculations. Moreover, we analyze the surface functionalization effect on the structural, vibrational, and electronic properties of the pristine ZnSb monolayer. The semi-fluorinated and fully-chlorinated ZnSb monolayers are shown to be dynamically stable in contrast to the ZnSb monolayer. At the same time, semi-fluorination and fully-chlorination of ZnSb monolayer could effectively modulate the metallic electronic properties of pristine ZnSb. In addition, a magnetic metal to a nonmagnetic semiconductor transition with a band gap of 1 eV is achieved via fluorination, whereas a transition to a semiconducting state with 1.4 eV band gap is found via chlorination of the ZnSb monolayer. According to the optical properties analysis, the first absorption peaks of the fluorinated- and chlorinated-ZnSb monolayers along the in-plane polarization are placed in the infrared range of spectrum, while they are in the middle ultraviolet for the out-of-plane polarization. Interestingly, the optically anisotropic behavior of these novel monolayers along the in-plane polarizations is highly desirable for design of polarization-sensitive photodetectors. The results of the calculations clearly proved that the tunable electronic properties of the ZnSb monolayer can be realized by chemical functionalization for application in the next generation nanoelectronic devices.

The optical, electronic, and structural properties of a theoretically predicted new boron–carbon–nitride (BCN) two-dimensional monolayer have been explored using density functional theory calculations. The phonon dispersion, molecular dynamics simulation, the cohesive energy, and the Born criteria of elastic constant calculations of the BCN monolayer confirm its stability. The phonon spectrum illustrates an out-of-plane flexure mode with quadratic dispersion in the long-wavelength limit. The BCN monolayer is a semiconductor with a direct bandgap of 0.9 (1.63) eV determined via the Perdew–Burke–Ernzerhof (Heyd–Scuseria–Ernzerhof) functional. The same electron and hole effective masses and mobility values indicate the high recombination rate of electrons and holes. Meanwhile, the BCN monolayer can absorb ultraviolet radiation more effectively than visible light. Due to its interesting physical properties, the novel BCN monolayer could be a rather good candidate material for electro-optical applications.

Recently, a two-dimensional (2D) MoSi2N4 (MSN) structure has been successfully synthesized [Hong et al., Science 369(6504), 670–674 (2020)]. Motivated by this result, we investigate the structural, electronic, and optical properties of MSN monolayer (MSN-1L) and bilayer (MSN-2L) under the applied electric field (E-field) and strain using density functional theory calculations. We find that the MSN-2L is a semiconductor with an indirect bandgap of 1.60 (1.80) eV using Perdew–Burke–Ernzerhof (HSE06). The bandgap of MSN-2L decreases as the E-field increases from 0.1 to 0.6 V/Å and for larger E-field up to 1.0 V/Å the bilayer becomes metallic. As the vertical strain increases, the bandgap decreases; more interestingly, a semiconductor to a metal phase transition is observed at a strain of 12%. Furthermore, the optical response of the MSN-2L is in the ultraviolet (UV) region of the electromagnetic spectrum. The absorption edge exhibits a blue shift by applying an E-field or a vertical compressive strain. The obtained interesting properties suggest MSN-2L as a promising material in electro-mechanical and UV opto-mechanical devices.