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α-Al2O3 is renowned for its extensive bandgap and diverse applications in electronic and optoelectronic devices. Employing density-functional theory-based methods, this study investigates the feasibility of chalcogen doping (S, Se, Te) in α-Al2O3. Standard modeling tools are utilized to construct α-Al2O3 supercells, focusing on the calculations of individual chalcogen-related and native point defects resulting from single-atom doping. Our analysis systematically explores the formation energies and transition levels associated with chalcogen (S, Se, Te) doping in oxygen (or aluminum) sites in Al-rich (or O-rich) limits. We observe a trend where increasing atomic number (from S to Te) correlates with a higher difficulty in forming anion-doped α-Al2O3, but a lower barrier to cationic doping. The results indicate a preferential substitution of chalcogen atoms for aluminum in O-rich environments. Specifically, in varying oxygen conditions, the dominant defect types, their prevalence, and defect formation energies in α-Al2O3 are significantly altered following chalcogen doping, offering new insights into defect processes in α-Al2O3. [ABSTRACT FROM AUTHOR]

In recent years, memristors have garnered significant attention, particularly those based on the oxygen vacancy-driven filamentary conduction mechanism. However, studies utilizing single-crystal materials for memristors remain scarce. This study investigates memristive effect of Se-implanted β-Ga2O3 single-crystal material, fabricated through ion implantation. X-ray photoelectron spectroscopy and depth profiling revealed that Se doping significantly increased the concentration of oxygen vacancies, crucial for resistive switching (RS). Electrical testing demonstrated stable and repeatable resistive switching behavior, attributed to the filamentary conduction mechanism driven by oxygen vacancies. These findings highlight the potential of ion implantation for tuning the surface properties of Ga2O3-based memristors, advancing their application in next-generation electronic devices. [ABSTRACT FROM AUTHOR]

This study is the first to explore the effect of selenium doping on the electronic properties of β-Ga2O3 through first-principles calculations. Selenium doping in β-Ga2O3 is a significant choice, as it has the potential to improve the material's electronic properties. Previous work on β-Ga2O3 has focused primarily on other dopants, and the effect of selenium doping is not well understood. Therefore, this study fills an important gap in the current understanding of β-Ga2O3 doping. Selenium doping in β-Ga2O3 was studied by first-principles calculations with a hybrid functional, as this functional can offer a more accurate description of electronic properties, resulting in accurate electronic bandgap and defect level calculations. Our first-principles calculations reveal that selenium can be incorporated on both Ga and O sites under specific conditions. Specifically, under O-rich conditions, selenium atoms are more likely to substitute the Ga sites, whereas under Ga-rich conditions, they are more likely to substitute the O sites. With the formation energy analysis, our findings indicate that selenium doping on Ga sites can lead to n-type conductivity, with it acting as shallow donor. On the other hand, Se dopants at the O sites exhibit deep donor characteristics, rendering it ineffective in regulating the conductivity of β-Ga2O3 materials. Our findings suggest that Se can be used as a dopant to tune the β-Ga2O3 conductivity for electronic and photonic applications, provided that the atomic substitution on Ga sites can be effectively controlled. Our results will provide valuable theoretical insights for the refined use of selenium dopants in β-Ga2O3, as well as guidance and theoretical support for subsequent researchers in the selection of Ga2O3 dopants. [ABSTRACT FROM AUTHOR]

The emergent van der Waals semiconductor GaPS4 is heralding frontiers for gallium-based semiconductors. Despite its potential, the intricacies of its Raman spectrum and phonon heat transport remain elusive. In this research, experimental and theoretical methods are employed to give a comprehensive portrayal. The Raman spectra and phonon calculations obtained were cross-validated, affirming the study's credibility. A total of 28 Raman peaks were identified, with all phonon irreducible representations delineated. Advanced calculations unveiled notable shifts in the transition of GaPS4 from bulk to monolayer. During this process, phonons undergo a red shift, and the vibration contributions of different atoms change. The lifetime and group velocity of low wavenumber phonons are markedly reduced, suppressing the thermal conductivity in the monolayer. The thermal conductivity of GaPS4 bulk at 300 K is 0.5 W/m K, and 0.13 W/m K for monolayer, while the thermal conductivity in the cleavage direction is lower. These findings offer a detailed account of the complex Raman spectra and phonon thermal transport properties of GaPS4, setting the stage for its subsequent exploration and prospective applications in electronic and thermal devices, and contributing to enriching condensed matter theory of phonon thermal transport in van der Waals materials. [ABSTRACT FROM AUTHOR]

Density functional theory computations were utilized to quantify the polarization discontinuity of 1.8 μC/cm2 in ε-(B0.0625Ga0.9375)2O3/ε-Ga2O3 heterostructure. The polarization effect was sufficient to generate a two-dimensional electron gas (2DEG) at the heterostructure interface without doping. The creation of 2DEG occurred when the BGaO layer thickness exceeded 17 nm, with its density exhibiting a logarithmic increase as the thickness was augmented. However, the trend plateaued when the thickness surpassed 80 nm with a carrier density of 8.17 × 1012 cm–2. Moreover, guided by Griffith's theory and enthalpy calculations, the epitaxial layer could potentially be pseudomorphically grown up to 968 nm under growth conditions of 1000 K with dilute boron alloying. This design heralds the potential for creating a high electron mobility transistor based on ε-BGaO with an epitaxial layer just nanometers thick, well-suited for high-power and radio frequency applications. [ABSTRACT FROM AUTHOR]

Spintronics devices have been a research hotspot due to their rich theoretical and application value. The widebandgap semiconductor β-Ga2O3 has excellent application potential in spintronics due to the controllability of its electron behavior via ultraviolet light. This paper employs first-principles calculations and the Wenzel–Kramers–Brillouin (WKB) approximation to comprehensively investigate spin transport based on magnetic tunnel junctions (MTJs) comprising β-Ga2O3 nanosheets. The magnetic moment of the ferromagnetic layer in β-Ga2O3 MTJs is found to be positively correlated with tunnel magnetoresistance (TMR). Interestingly, layer-number parity-dependent oscillation of TMR in β-Ga2O3 MTJs is observed, which is explained by the non-equilibrium Green function and the WKB approximation. TMR reaches a maximum of 1077% at five layers, and bias-dependent stability is observed in the monolayer model under biases of 0–20 mV. This study not only expands the application potential of β-Ga2O3 and predicts its superiority in spintronics but also enriches the related condensed matter theory. [ABSTRACT FROM AUTHOR]

First-principles calculations were employed to determine the surface energy and fracture toughness of monoclinic Ga2O3 and (InxGa1−x)2O3 alloy with In content up to 37.5%. The lattice parameters and elastic constants of (InxGa1−x)2O3 alloys are calculated and followed Vegard's law with an increasing In concentration. The most probable crack planes for each growth orientation, [100], [010] and [001], are determined through comparison with the surface energy and fracture toughness of monoclinic Ga2O3. In addition, the critical thicknesses of the (InxGa1−x)2O3 epitaxial film grown on the Ga2O3 substrate in [100], [010] and [001] orientations were found to be 40 nm, 35 nm and 36 nm, respectively at an In content up to 37.5%, suggesting reasonable pseudomorphic growth conditions for (InxGa1−x)2O3/Ga2O3 heterostructure formation. Based on the analysis of bond lengths, dangling bonds and surface coordination, the stability of the surface in the (100) direction with surface terminations including Ga and O atoms was found to have lower fracture toughness than the other surfaces, implying that epitaxial growth with the (100) crack surface might result in lower defects with a higher film thickness. Overall, the cracking mechanisms in the (InxGa1−x)2O3 film grown on the Ga2O3 substrate with different orientations are elucidated. [ABSTRACT FROM AUTHOR]

In this work, an 8×8 Ga2O3 solar-blind ultraviolet photodetector array is introduced for image sensing application. The 2-in wafer-scaled Ga2O3 thin film was grown by metalorganic chemical vapor deposition technique; and the photodetector array was fabricated through ultraviolet photolithography, lift-off, and electron-beam evaporation. In addition to the high solar-blind/visible rejection ratio of 104, every photodetector cell in the array has high performance and fast response speed, such as responsivity of 49.4 A W−1, specific detectivity of 6.8 × 1014 Jones, external quantum efficiency of 1.9 × 104%, linear dynamic range of 117.8 dB, and response time of 41 ms, respectively, indicating the high photo-response performance of the photodetector. Moreover, the photodetector array displayed uniform responsivity with a standard deviation of ∼6%, and presented a sensing image of low chromatic aberration, owing to the high resolution of the photodetector array. In a word, this work may contribute to developing Ga2O3-based optoelectronic device applications. [ABSTRACT FROM AUTHOR]

The low thermal conductivity of β-Ga2O3 single crystal imposes limitations on its device performance under high-temperature and high-power conditions. Phonons are widely recognized to play the main role in heat transport, while the anharmonic scattering among these quasi-particles significantly diminishes thermal conductivity. Therefore, investigating the anharmonic phonon scattering within β-Ga2O3 single crystal holds paramount significance. In this study, we mainly employed temperature-dependent Raman spectroscopy and first-principles calculation to give a quantitative analysis on the anharmonic phonon scattering. The mode Grüneisen parameters and temperature-dependent thermal expansion coefficient were studied. Strong anharmonic phonon scattering was also confirmed, which was mainly caused by cubic scattering, but quartic scattering is also nonnegligible and causes nonlinear linewidth broadening. Moreover, high wavenumber peaks are more likely to undergo asymmetric phonon scattering by comparing the symmetric and asymmetric scattering models. In all, this study provides a profound understanding of the anharmonic phonon scattering properties within the β-Ga2O3 single crystal. It enriches our understanding of quasi-particle interaction dynamics and offers theoretical pathways for expanding the applications of β-Ga2O3 single crystal and optimizing its device performance. [ABSTRACT FROM AUTHOR]

In this study, we present an investigation of the spontaneous and piezoelectric polarization in the ε-(AlxGa1–x)2O3/ε-Ga2O3 heterostructures using density functional theory calculations. The spontaneous polarization (Psp) was found to increase from 23.93 to 26.34 μC/cm2 when Al-content increase from 0% to 50%. With Al-content increasing, the strain-induced piezoelectric polarization (Ppe) increases, which negates the Psp, causing the total polarization (Ptot) of the epitaxy layer in the AlGaO/GaO heterostructure to remain almost constant across all Al compositions. Additionally, due to the ferroelectric nature of ε-Ga2O3, a high-density polarization-induced two-dimensional electron gas (2DEG) can be formed at the interface of polarization reversed ε-(AlxGa1–x)2O3/ε-Ga2O3 when an electric field is applied. Using the 1D Schrödinger–Poisson model, the 2DEG of polarization reversed ε-(Al0.125Ga0.875)2O3/ε-Ga2O3 was found to be 2.05 × 1014 cm−2, which is nearly ten times larger than that of GaN-based structures. Our work indicates that ε-(AlxGa1–x)2O3/ε-Ga2O3 heterostructure could play a key role attributed to the large polarization and capability in modulating the polarization for high-power electronic and radio frequency device applications. [ABSTRACT FROM AUTHOR]