Ultra-wide Bandgap Research Articles

Blue-Noise-Based Disordered Photonic Structures Show Isotropic and Ultrawide Band Gaps

Spatially disordered but uniformly distributed point patterns characterized by so-called blue-noise long-range spatial correlations are of great benefit in computer graphics, especially in spatial dithering thanks to the spatial isotropy. Herein, the potential photonic properties of blue-noise disordered, homogeneous point processes based on farthest-point optimization are numerically investigated for silicon photonics. The photonic properties of blue-noise two-dimensional patterns are studied as a function of the filling fraction and benchmarked with photonic crystals with a triangular lattice. Ultrawide and omnidirectional photonic band gaps spanning most of the visible spectrum are found with estimates of gap–midgap ratios of up to 55.4% for transverse magnetic polarization, 59.4% for transverse electric polarization, and 32.7% for complete band gaps. The waveguiding effect in azimuthal defect lines is also numerically evaluated. These results corroborate the idea that long-range correlated disordered structures are helpful for engineering novel devices with the additional degree of freedom of spatial isotropy, and capable of bandgap opening even without total suppression of infinite-wavelength density fluctuations.

First-principles investigation of the ultra-wide band gap halides perovskite XBeF3 (X = Na, K) with pressure effects

Based on the first-principles and quasi-harmonic Debye model, the structure, electronic, optical and thermodynamic properties of XBeF3 (X = Na, K) crystals at 0 ∼ 30 GPa are systematically investigated for the first time. The lattice constant, elastic constants, and bulk modulus of NaBeF3 and KBeF3 crystals are calculated under zero temperature and zero pressure, which are consistent with the literature values. The studies of electronic properties show that the ultra-wide band gaps of NaBeF3 and KBeF3 crystals at 0 GPa are 7.096 eV and 7.720 eV, respectively. Their band gaps increase with increasing pressure, while their type is indirect without the influence of pressure. Besides, the band structure of XBeF3 crystals at 0 ∼ 30 GPa is calculated by HSE06 functional. The variation of the XBeF3 band gap calculated by the HSE06 function with pressure is consistent with the trend of GGA functional. Additionally, the optical properties including reflectivity, absorption coefficient, complex refractive index, dielectric function and conductivity of NaBeF3 and KBeF3 crystals from 0 to 30 GPa have been comprehensively investigated. Using the quasi-harmonic Debye model, the relative volume, expansion coefficient, Debye temperature and heat capacity effect with pressures and temperatures of NaBeF3 and KBeF3 at 0 ∼ 30 GPa are also researched. The Debye temperatures of NaBeF3 and KBeF3 at 300 K are calculated to be 656.38 K and 602.6 K respectively. At relatively high temperature, the heat capacity at constant volume gradually approaches the Dulong-Petit limit. The results in this paper show that NaBeF3 and KBeF3 crystals may be used in the fields of lens materials and window materials in the deep ultraviolet range. Additionally, the ultra-wide band gap characteristics of NaBeF3 and KBeF3 enable them to be useful as highly insulating layers and high-voltage capacitors.

Design and investigated a novel BN polymorph in orthorhombic phase

In this work, a new BN polymorph with Pnma symmetry is proposed by RG2 and investigated by density functional theory. Pnma-II BN polymorph is shown to be dynamically and mechanically stable, and the relative enthalpy of Pnma-II BN is 0.187 eV per atom higher than that of c-BN, respectively. Mechanical properties calculations indicate that Pnma-II BN is also a potential superhard material with hardness of 49.7 GPa. The electronic band structures of Pnma-II BN show that the Pnma-II BN is a direct and ultrawide band gap semiconductor (band gap is 5.82 eV). The mechanical anisotropy of Young's modulus of Pnma-II BN and Pnma BN is greater than that of c-BN, while the mechanical anisotropy of shear modulus of Pnma-II BN in the (100), (001) plane is lower than that of c-BN. In addition, simulated X-ray diffraction patterns are provided for experimental confirmation of the predicted structures.

Photocarrier transport reconstruction and dramatical performance enhancement in ultrawide-bandgap ε-Ga2O3 photodetectors via surface defect passivation

The semiconductor surface is a major platform dictating carrier transport and recombination, in particular for planar photoconductive devices such as metal-semiconductor-metal (MSM) photodetectors. Here we demonstrate the integration of an ultrathin Al2O3 capping layer to effectively passivate the surface defects of epitaxial ε-Ga2O3 films and substantially enhance the photodetector performance. Incorporating an Al2O3 layer is found to significantly reduce the dark current of ε-Ga2O3 MSM photodetectors by more than three orders of magnitude, and simultaneously enhance the photocurrent and the response speed. With an ultrathin Al2O3 surface layer, the Al2O3/ε-Ga2O3 MSM photodetector achieves a superhigh responsivity of >104 A/W, a detectivity of >1016 Jones with a photo-to-dark ratio of >107, an UV–vis rejection ratio of >104 and millisecond response time for continuous-wave illumination. The surface passivation mechanism is analyzed by combined X-ray photoemission spectroscopy, secondary ion mass-spectroscopy and numerical calculations. It is revealed that the Al2O3 capping layer passivates the surface defects that are in the form of reduced tin species and oxygen vacancies, and reconstructs a faster surface transport channel for more efficient photocarrier collection. This study expands the design concept of surface passivation with ultrawide bandgap semiconductors for developing efficient deep ultraviolet photodetectors.

Power Electronics Revolutionized: A Comprehensive Analysis of Emerging Wide and Ultrawide Bandgap Devices.

This article provides a comprehensive review of wide and ultrawide bandgap power electronic semiconductor devices, comparing silicon (Si), silicon carbide (SiC), gallium nitride (GaN), and the emerging device diamond technology. Key parameters examined include bandgap, critical electric field, electron mobility, voltage/current ratings, switching frequency, and device packaging. The historical evolution of each material is traced from early research devices to current commercial offerings. Significant focus is given to SiC and GaN as they are now actively competing with Si devices in the market, enabled by their higher bandgaps. The paper details advancements in material growth, device architectures, reliability, and manufacturing that have allowed SiC and GaN adoption in electric vehicles, renewable energy, aerospace, and other applications requiring high power density, efficiency, and frequency operation. Performance enhancements over Si are quantified. However, the challenges associated with the advancements of these devices are also elaborately described: material availability, thermal management, gate drive design, electrical insulation, and electromagnetic interference. Alongside the cost reduction through improved manufacturing, material availability, thermal management, gate drive design, electrical insulation, and electromagnetic interference are critical hurdles of this technology. The review analyzes these issues and emerging solutions using advanced packaging, circuit integration, novel cooling techniques, and modeling. Overall, the manuscript provides a timely, rigorous examination of the state of the art in wide bandgap power semiconductors. It balances theoretical potential and practical limitations while assessing commercial readiness and mapping trajectories for further innovation. This article will benefit researchers and professionals advancing power electronic systems.

Abrasive machining induced surface layer damage behavior and formation mechanism of monocrystalline β-Ga2O3: A comparative study of nanoindentation and nanogrinding

Beta-phase gallium oxide (β-Ga2O3) has garnered significant attention in recent years as an ultra-wide bandgap semiconductor material. However, its surface layer damage behavior and machining deformation mechanism remain poorly understood. In this work, a systematic comparative study was conducted through nanoindentation and nanogrinding for monocrystalline β-Ga2O3 (−201) crystal plane. Transmission electron microscopy is employed as the primary characterization method. The results show that the microstructural evolution patterns of monocrystalline β-Ga2O3 can be categorized into four stages, i.e. stacking faults, twins, slip bands, and cleavage cracks are observed sequentially. According to the tests results, subsurface damage diagram models based on nanoindentation and nanogrinding are established, both of which exhibit the above evolution patterns as the indentation depth and grit depth of cut increases. However, there are some differences. In the nanogrinding process, nanocrystals and amorphous layers were found near the ground surface, which are related to the high strain rate grinding conditions and the unique material properties of monocrystalline β-Ga2O3 with low stacking fault energy. The results in this work contribute to an enhanced understanding of the deformation characteristics of monocrystalline β-Ga2O3 at macro and micro scales, while offering valuable insights for achieving damage control in ultra-precision machining processes.

Tremendous enhancement of green emission from Er3+/In3+ co-doped β-Ga2O3 ultrawide bandgap semiconductors

Er3+ singly doped and Er3+/In3+ co-doped gallium oxide ceramics with intense green emission were prepared using the conventional solid-state reaction method. The Ga2-x-yErxInyO3 ceramics exhibit green and red emission at 555 and 673 nm, and follow the two-photon absorption process under the excitation of 980 nm. Systematic measurements of the upconversion luminescence spectra of Ga2-x-yErxInyO3 show that the optimal doping concentrations, sintering temperature and time are x = 0.015, y = 0.035, 1250 °C, and 8 h, respectively. For a fixed Er3+ doping concentration of x = 0.015, the green emission intensity at 555 nm can be enhanced by 60 folds through 3.5 mol% In3+ doping, which is attributed to reduced non-radiative decay, enhanced energy transfer from In3+ ions to Er3+ ions via defect states, and increased photon absorption. The introduction of 3.5 mol% In3+ also increases the fluorescence lifetime by 235–272%. These observations provide compelling evidence for the presence of effective energy transfer between In3+ and Er3+ ions.

First-Principles Study Combined with Interpretable Machine-Learning Models of Bayesian Optimization for the Design of Ultrawide Bandgap Double Perovskites

First-Principles Study Combined with Interpretable Machine-Learning Models of Bayesian Optimization for the Design of Ultrawide Bandgap Double Perovskites

Toward Sustainable Ultrawide Bandgap van der Waals Materials: An ab initio Screening Effort

AbstractThe sustainable development of next‐generation device technology is paramount in the face of climate change and the looming energy crisis. Tremendous effort is made in the discovery and design of nanomaterials that achieve device‐level sustainability, where high performance and low operational energy cost are prioritized. However, many of such materials are composed of elements that are under threat of depletion and pose elevated risks to the environment and human health. The role of materials‐level sustainability in computational screening efforts is overlooked thus far. This work presents a general van der Waals materials screening framework imbued with sustainability‐motivated search criteria. Using ultrawide bandgap (UWBG) materials as a backdrop, 25 sustainable UWBG layered materials comprising only of low‐risks elements result from this screening effort, with several meeting the requirements for dielectric, power electronics, and ultraviolet device applications. These findings constitute a critical first‐step toward reinventing a more sustainable electronics landscape beyond silicon, with the framework established in this work serving as a harbinger of sustainable 2D materials discovery.

Investigation and Evaluation of High-Temperature Encapsulation Materials for Power Module Applications

With the advent of ultra-wide bandgap (UWBG) semiconductor materials, such as Gallium Oxide (Ga2O3) and Aluminum Nitride (AlN), higher temperature and higher voltage operation of power devices is becoming realizable. However, conventional polymeric and organic encapsulant materials are typically limited to operating temperatures of 200 °C and below. In this work, six materials were identified and evaluated as candidates for use as encapsulants for operation and high-voltage insulation at and above 250 °C. High-temperature silicone gel was used as a reference material and was compared to five novel encapsulants including an epoxy resin, a hydro-set cement, two low melting point glass compounds, and a ceramic potting compound. Gas pycnometry was utilized to evaluate the voiding concentration to avoid partial discharge. Each material was then processed onto a direct-bonded-aluminum (DBA) substrate test coupon to evaluate compatibility with a commonly used metal-ceramic substrate and processability for use in a power module. The insulation capability of each material was evaluated by testing the partial discharge inception voltage (PDIV) across a 1mm gap etched in the substrate. The dielectric stability was then tested by soaking the materials in air at 250 °C for various intervals and observing the degradation of their PDIVs and appearances. The results of each test were compared, and conclusions were drawn about each material’s feasibility for use as a dielectric encapsulation material for a power module operating at temperatures exceeding 200 °C.

Native defects association enabled room-temperature p-type conductivity in β-Ga2O3

The room temperature hole conductivity of the ultra-wide bandgap semiconductor β-Ga2O3 is a pre-requisite for developing the next-generation electronic and optoelectronic devices based on this oxide. In this work, high-quality p-type β-Ga2O3 thin films grown on r-plane sapphire substrate by metalorganic chemical vapor deposition (MOCVD) exhibit ρ = 5 × 104 Ω·cm resistivity at room temperature. A low activation energy of conductivity as Ea2 = 170 ± 2 meV was determined, associated to the VO++−VGa−native acceptor defect complex. Further, taking advantage of cation (Zn) doping, the conductivity of Ga2O3:Zn film was remarkably increased by three orders of magnitude, showing a long-time stable room-temperature hole conductivity with the conductivity activation energy of around 86 meV. VO++−ZnGa− defect complex has been proposed as a corresponding shallow acceptor.

The role of oxygen vacancies in Ga2O3-based solar-blind photodetectors

Gallium oxide (Ga2O3) with an ultrawide bandgap, is a promising and inherent material for solar-blind photodetectors (SBPDs). However, it remains a challenge to achieve a photodetector with large responsivity and fast response speed owing to the presence of intrinsic oxygen vacancies (VO) in the Ga2O3 films. Here, the annealing and doping engineering is proposed to break the compromise between the responsivity and response speed, based on the low-cost method for annealing nitrogen-doped Ga2O3 films with various concentrations of VO in Ar, O2, and N2 atmospheres. The mechanism of regulating VO in the nitrogen-doped Ga2O3 films under various annealing atmospheres has been clarified first. The influence of concentrations of VO in pristine films and annealing atmospheres on the photoelectric properties of annealed films was analyzed systematically. The nitrogen-doping, recrystallization, and the appropriate concentration of VO in pristine Ga2O3 films are favorable factors for optimizing the properties of the post-annealing Ga2O3 films. The photodetectors based on annealing and doping engineering exhibit impressive characteristics with high photo-to-dark current ratios (PDCRs) of 2.6 × 107, large rejection ratio of R254 /R365 = 1.0 × 106, especially the faster response speed of 0.359/0.110 s, 9.8 times higher R254, and 6.34 × 102 times lower Idark than pristine films. The regulation of VO via doping and annealing methods can provide an effective strategy for low-cost high-performance Ga2O3-based SBPDs.

Novel vibration self-suppression of periodic pipes conveying fluid based on acoustic black hole effect

The pipes conveying fluid are concerned as extremely significant fluid-solid coupling structures due to the extensive application in the many engineering fields, but poor operating performances induced by unexpected vibration may destroy the related devices in the piping structures. To effectively attenuate the fluid-solid coupling vibration, a novel control technique is proposed to realize the vibration self-suppression of pipes conveying fluid with integration of the periodic acoustic black hole (ABH) wedges inspired by the extraordinary band gaps (BGs) behaviors of the metamaterials. On the basis of the Euler-Bernoulli (E-B) beam model, the mechanical model and dynamic equations are established by using Hamilton's principle. By applying the spectral element method (SEM) in conjunction with the transfer matrix method (TMM), as well as considering the Bloch theorem, the mechanism of elastic-wave distributions of such periodic ABH pipes conveying fluid are disclosed through investigating the BGs characteristic, frequency response and wave shapes. The results show the proposed technique can effectively form BGs in low frequency bands, and most of the energies are absorbed and scattered by the wedge edge of the pipes in the wave propagation. More importantly, by adjusting the system parameters, the proposed structure can enlarge the BGs regions and transfer it to the low frequency bands. It provides a simple design scheme for the manufacture of pipe conveying fluid with ultra-wide BGs.

Novel two-dimensional square-structured diatomic group-IV materials: the first-principles prediction

This work presents a study of novel two-dimensional (2D) square-structured diatomic group-IV materials through density functional theory calculations. Our optimized structures have a planar structure. Moreover, we evaluate the structural stabilities and electronic properties of six square-structured 2D-diatomic XY (X, Y = C, Si, Ge, Sn) materials. In comparison, we also evaluate the honeycomb structure of those materials. The Birch-Murnaghan equation of states (BM-EOS) curves and cohesive energy evaluations indicate that the square-structured SnGe and SnSi materials are highly stable. Interestingly, most of the square-structured materials are dynamically stable based on phonon dispersion evaluation, except SnC material. More importantly, most of the square-structured materials have a narrower bandgap energy which implies better electronic properties. In particular, square-structured SnGe shows an ultra-wide bandgap of 4.02 eV which is prospective for future electronics. Furthermore, we believe that the stable square structures will be observed in the experiment and will be beneficial for future device applications.

A wide ultraviolet spectra response photodetector based on epitaxial growth of highly-oriented ε-Ga2O3 crystal on diamond substrate

In recent years, diamond has shown great potential in solar-blind ultraviolet (UV) photodetection due to its ultrawide bandgap (∼ 5.5 eV) and other superior semiconductor properties. However, the response region of diamond photodetector is usually smaller than 230 nm, which cannot cover the whole solar-blind region from 200 to 280 nm. In this work, an ε-Ga2O3/diamond photodetector with wide spectra responsivity from 210 (or even lower) to 260 nm was fabricated. High-quality ε-Ga2O3 film with columnar crystal was epitaxially grown on single crystalline CVD diamond substrate by pulse laser deposition (PLD). TEM characterization revealed that the ε-Ga2O3 film grew along the <001> orientation on diamond (100) substrate. The deep ultraviolet (DUV) photodetector based on the ε-Ga2O3/diamond structure showed a high light-to-dark ratio over 5.7 × 104 and good linear response to the incident light power density from 10 to 400 mW/cm2. Moreover, compared to other photodetectors, the fabricated ε-Ga2O3/diamond photodetector achieved high responsivity and wide spectra response region from 210 to 260 nm, with high solar-blind rejection ratio of 104 (R 240/R 280) and 165 (R 210/R 280), respectively. The extension of spectra region with high responsivity of the ε-Ga2O3/diamond photodetector can be attributed to the thin thickness of ε-Ga2O3 film (around 200 nm) and parts of the DUV light were absorbed by diamond. The high responsivity and wide spectra response region indicate the fabricated ε-Ga2O3/diamond photodetector can be used for the detection of ultraviolet in the most of the DUV region.

Radiation hardness evaluation of ε-Ga2O3 thin-film devices under swift heavy ion irradiation

The ultra-wide band gap (∼4.9 eV) and extremely large breakdown field strength (∼8 MV/cm) enable ε-Ga2O3 as an ideal materials candidate for high-performance power devices and solar-blind photodetectors. For the purpose of deep space applications explorations, comprehensive study of the effects of particle irradiation on the lattice stability and electronic properties of ε-Ga2O3 are of pivotal importance. In this work, leveraging a unique Ta radiation source, we interrogate the radiation hardness of ε-Ga2O3 thin films after 1907 MeV Ta swift heavy ion (SHI) irradiation. Detailed characterizations of the structural and optical properties show that the morphology and lattice structure are disrupted, with an increase of the band gap. Additionally, X-ray photoelectron spectroscopy experiments combining density functional theory calculations corroborate extrinsic flux-induced high concentration defects in the film, which lead to truncated photo-response performance of the device. However, even upon irradiation with a fluence of 5 × 1010 cm−2, the overall performance of the device remains robust and substantial. This outstanding radiation hardness of ε-Ga2O3 thin films rationalizes their potential usage for space applications.

Thermal conductivity at finite temperature and electronic structure of the ultra-wide band gap fluorinated 2D GaN

Passivation makes 2D hexagonal structure more stable than the planar variant. Surface fluorinated monolayer of GaN have been found to have ultra-wide band gap and have promising applications in optoelectronic conversion devices. In this work, using theoretical method, we have explored the thermal conductivity as well as the electronic structure of F–GaN. It has a low thermal conductivity of 7.67 W (mK)−1 due to the low group velocity and short phonon lifetime. The calculated direct band gap value is 4.63 eV, which could be modulated by strain and biaxial strain is found to more effective. Attractively, direct band gap can be maintained under tensile strain. Breakdown of symmetry by uniaxial strain lifts the band degeneracy of the VBM, which will lead to polarized light emission. The in-depth analysis shows that Ga–F as well as N–F bonds are strongly ionic, which is responsible for its low thermal conductivity and ultra-wide band gap.

A Highly Transparent β-Ga2O3 Thin Film-Based Photodetector for Solar-Blind Imaging

Ultra-wide bandgap Ga2O3-based optoelectronic devices have attracted considerable attention owing to their special significance in military and commercial applications. Using RF magnetron sputtering and post-annealing, monoclinic Ga2O3 films of various thicknesses were created on a c-plane sapphire substrate (0001). The structural and optical properties of β-Ga2O3 films were then investigated. The results show that all β-Ga2O3 films have a single preferred orientation (2(_)01) and an average transmittance of more than 96% in the visible wavelength range (380–780 nm). Among them, the sample with a 90-minute sputtering time has the best crystal quality. This sample was subsequently used to construct a metal-semiconductor-metal (MSM), solar-blind, ultraviolet photodetector. The resulting photodetector not only exhibits excellent stability and sunblind characteristics but also has an ultra-high responsivity (46.3 A/W) and superb detectivity (1.83 × 1013 Jones). Finally, the application potential of the device in solar-blind ultraviolet imaging was verified.

Gallium Oxide Heterojunction Diodes for 400 °C High‐Temperature Applications

β‐Ga2O3‐based semiconductor devices are expected to have significantly improved high‐power and high‐temperature performance due to its ultrawide bandgap of close to 5 eV. However, the high‐temperature operation of these ultrawide‐bandgap devices is usually limited by the relatively low 1–2 eV built‐in potential at the Schottky barrier with most high‐work‐function metals. Herein, heterojunction p‐NiO/n‐β‐Ga2O3 diodes fabrication and optimization for high‐temperature device applications are reported, demonstrating a current rectification ratio (ION/IOFF) of more than 106 at 410 °C. The NiO heterojunction diode can achieve higher turn‐on (VON) voltage and lower reverse leakage current compared to the Ni‐based Schottky diode fabricated on the same single‐crystal β‐Ga2O3 substrate, despite charge transport dominated by interfacial recombination. Electrical characterization and device modeling show that these advantages are due to a higher built‐in potential and additional band offset. These results suggest that heterojunction p–n diodes based on β‐Ga2O3 can significantly improve high‐temperature electronic device and sensor performance.

Investigation of Phase Transition and Ultrawide Band Gap Engineering in MgGaO Semiconductor Thin Films

Investigation of Phase Transition and Ultrawide Band Gap Engineering in MgGaO Semiconductor Thin Films