Improved High Z, Wide Band Gap Semiconductors through Modeling and Experiment
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73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
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Results for “Band gap”
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Efficient wide-band-gap copolymer donors for organic solar cells with perpendicularly placed benzodithiophene units
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99 GENERAL AND MISCELLANEOUS↗
First-principles calculations of structural, electrical, and optical properties of ultra-wide bandgap (Al$_x$Ga$_{1-x}$)$_2$O$_3$ alloys
Alloys between Ga 2 O 3 and Al 2 O 3 (AGO) present a rich material space exhibiting numerous structural phases with unique optoelectronic properties that make them attractive candidates as ultra-wide bandgap (UWBG) semiconductors for next-generation power devices. Here we review the properties of AGO, focusing on theoretical results on the thermodynamics of Al incorporation and its consequences on the electronic structure. We review predictions and progress in experimentally realizing these alloys, as well as how composition influences important optoelectronic variables such as the band gap, band offsets, transport properties, and n-type dopability. A number of these parameters, such as the breakdown field (related to the band gap) and electron mobility, are discussed in assessing AGO in terms of relevant power device figures of merit. Altogether, the rapid progress and predicted properties highlight the promise of AGO as a model UWBG semiconductor platform with the potential to revolutionize power devices.
36 MATERIALS SCIENCE↗
Automated workflow for non-empirical Wannier-localized optimal tuning of range-separated hybrid functionals
Here, we introduce an automated workflow for generating non-empirical Wannier-localized optimally-tuned screened range-separated hybrid (WOT-SRSH) functionals. WOT-SRSH functionals have been shown to yield highly accurate fundamental band gaps, band structures, and optical spectra for bulk and 2D semiconductors and insulators. Our workflow automatically and efficiently determines the WOT-SRSH functional parameters for a given crystal structure and composition, approximately enforcing the correct screened long-range Coulomb interaction and an ionization potential ansatz. In contrast to previous manual tuning approaches, our tuning procedure relies on a new search algorithm that only requires a few hybrid functional calculations with minimal user input. We demonstrate our workflow on 23 previously studied semiconductors and insulators, reporting the same high level of accuracy. By automating the tuning process and improving its computational efficiency, the approach outlined here enables applications of the WOT-SRSH functional to compute spectroscopic and optoelectronic properties for a wide range of materials.
Gant, Stephen E. [University of California, Berkel↗
Band alignments and polarization properties of the Zn-IV-nitrides
Zn-IV-nitrides have a range of potential applications in electronic and optoelectronic devices and can be integrated with currently used III-nitride semiconductors and their alloys. Using hybrid density functional theory, we examine band gaps, band offsets, and polarization properties of the Zn-IV-nitrides and the ramifications of these properties on heterointerfaces formed between the Zn-IV-nitrides and III-nitrides. Here, we find a type-II band alignment between ZnGeN 2 and GaN, where the valence band of GaN is 0.28 eV above the valence band of ZnGeN 2 . Heterostructures between Zn-IV-nitrides and III-nitrides result in interface charges that allow for novel heterostructures and increased control over polarization fields. We find that an interface between In x Ga 1-x N and ZnGeN 2 can lead to zero interfacial polarization charge; however, the band alignments are unfavorable for carrier confinement in light-emitting devices. At the interface between AlN and ZnSiN 2 , we predict a large two-dimensional electron gas to form, confined to the ZnSiN 2 layer.
36 MATERIALS SCIENCE↗
Electron-Phonon Renormalization in the Proton-Conducting Electrolyte Ba Zr O 3 and Its Implications for High-Temperature Electrolysis
Electrical leakage is an inherent problem in solid-oxide fuel and electrolyzer cells, limiting their energy-conversion efficiency. High concentrations of electrons or holes can exacerbate this issue. However, it is largely unclear how the typical high operating temperatures of the systems influence their charge-carrier concentrations. In this work, we use first-principles calculations to examine how lattice vibrations impact electrical conductivity in conventional electrolytes, using Ba Zr O 3 as a representative material. Our analysis shows that phonon-induced shifts in the band gap and band edges lead to a dramatic increase in p -type carrier concentrations at temperatures above 600 K, compared to models that neglect temperature effects. Additionally, we reveal the importance of oxygen-ion motion on band-edge positions, which makes valence-band-edge shift dominate the band-gap change. Our study provides a protocol for calculating phonon-induced changes in similar oxides, paving the way for interrogating electrical leakage in electrolytes for high-temperature operation. Published by the American Physical Society 2025
25 ENERGY STORAGE↗
Diamond /111/ studied by electron energy loss spectroscopy in the characteristic loss region
Unoccupied surface states on diamond (111) annealed at greater than 900 C are studied by electron energy loss spectroscopy with valence band excitation. A feature found at 2.1 eV loss energy is attributed to an excitation from occupied surface states into unoccupied surface states of energy within the bulk band gap. A surface band gap of approximately 1 eV is estimated. This result supports a previous suggestion for unoccupied band gap states based on core level energy loss spectroscopy. Using the valence band excitation energy loss spectrosocpy, it is also suggested that hydrogen is removed from the as-polished diamond surface by a Menzel-Gomer-Redhead mechanism.
Pepper, S. V.↗
Superfluid weight cross-over and critical temperature enhancement in singular flat bands
Nonanalytic Bloch eigenstates at isolated band degeneracy points exhibit singular behavior in the quantum metric. Here, a description of superfluid weight for zero-energy flat bands in proximity to other high-energy bands is presented, where they together form a singular band gap system. When the singular band gap closes, the geometric and conventional contributions to the superfluid weight as a function of the superconducting gap exhibit different cross-over behaviors. The scaling behavior of superfluid weight with the band gap is studied in detail, and the effect on the Berezinskii–Kosterlitz–Thouless transition temperature is explored. It is found that tuning the singular band gap provides a unique mechanism for enhancing the supercurrent and critical temperature of two-dimensional superconductors.
Science & Technology - Other Topics↗
Three-Dimensional Lead Iodide Perovskitoid Hybrids with High X-ray Photoresponse
Large organic A cations cannot stabilize the 3D perovskite AMX 3 structure because they cannot be accommodated in the cubo-octhedral cage (do not follow the Goldschmidt tolerance factor rule), and they generally template low-dimensional structures. In this paper, we report that the large dication aminomethylpyridinium (AMPY) can template novel 3D structures which resemble conventional perovskites. They have the formula (xAMPY)M 2 I 6 (x = 3 or 4, M = Sn 2+ or Pb 2+ ) which is double of the AMX3 formula. However, because of the steric requirement of the Goldschmidt tolerance factor rule, it is impossible for (xAMPY)M 2 I 6 to form proper perovskite structures. Instead, a combination of corner-sharing and edge-sharing connectivity is adopted in these compounds leading to the new 3D structures. DFT calculations reveal that the compounds are indirect band gap semiconductors with direct band gaps presenting at slightly higher energies and dispersive electronic bands. The indirect band gaps of the Sn and Pb compounds are ~1.7 and 2.0 eV, respectively, which is slightly higher than the corresponding AMI 3 3D perovskites. The Raman spectra for the compounds are diffuse, with a broad rising central peak at very low frequencies around 0 cm –1 , a feature that is characteristic of dynamical lattices, high anharmonicity, and dissipative vibrations very similar to the 3D AMX 3 perovskites. Devices of (3AMPY)Pb 2 I 6 crystals exhibit clear photoresponse under ambient light without applied bias, reflecting a high carrier mobility (μ) and long carrier lifetime (τ). The devices also exhibit sizable X-ray generated photocurrent with a high μτ product of ~1.2×10 -4 cm 2 /V and a X-ray sensitivity of 207 μC∙Gy -1 ∙cm -2 .
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Pressure effect on band inversion in AE Cd 2 As 2 ( AE =Ca, Sr, Ba)
Recent studies have predicted that magnetic EuCd 2 As 2 can host several different topological states depending on its magnetic order, including a single pair of Weyl points. Here we report on the bulk properties and band inversion induced by pressure in the nonmagnetic analogs AECd 2 As 2 (AE = Ca, Sr, Ba) as studied with density functional theory calculations. Under ambient pressure we find that these compounds are narrow band gap semiconductors, in agreement with experiment. In this work, the size of the band gap is dictated by both the increasing ionicity across the AE series which tends to increase the band gap, as well as the larger nearest neighbor Cd-As distance from increasing atomic size which can decrease the band gap because the conduction band edge is an antibonding state derived mostly from Cd 5s orbitals. The combination of these two competing effects results in a nonmonotonic change of the band gap size across the AE series with SrCd 2 As 2 having the smallest band gap among the three compounds. The application of negative pressure reduces this band gap and causes the band inversion between the Cd 5s and As 4p orbitals along the Γ-A direction to induce a pair of Dirac points. The topological nature of the Dirac points is then confirmed by finding the closed Fermi arcs on the ($10\bar{1}0$) surface.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Field induced gap infrared detector
A tunable infrared detector which employs a vanishing band gap semimetal material provided with an induced band gap by a magnetic field to allow intrinsic semiconductor type infrared detection capabilities is disclosed. The semimetal material may thus operate as a semiconductor type detector with a wavelength sensitivity corresponding to the induced band gap in a preferred embodiment of a diode structure. Preferred semimetal materials include Hg(1-x)Cd(x)Te, x is less than 0.15, HgCdSe, BiSb, alpha-Sn, HgMgTe, HgMnTe, HgZnTe, HgMnSe, HgMgSe, and HgZnSe. The magnetic field induces a band gap in the semimetal material proportional to the strength of the magnetic field allowing tunable detection cutoff wavelengths. For an applied magnetic field from 5 to 10 tesla, the wavelength detection cutoff will be in the range of 20 to 50 micrometers for Hg(1-x)Cd(x)Te alloys with x about 0.15. A similar approach may also be employed to generate infrared energy in a desired band gap and then operating the structure in a light emitting diode or semiconductor laser type of configuration.
Elliott, C. Thomas↗
Anomalous elastic softening in ferroelectric hafnia under pressure
his study employs first-principles density-functional theory (DFT) calculations to explore the elastic and mechanical properties of ferroelectric hafnia (HfO 2 ) in its polar orthorhombic 𝑃𝑐𝑎2 1 phase under varying hydrostatic pressure conditions up to 30 GPa. Utilizing a plane-wave basis set and Perdew-Burke-Ernzerhof generalized-gradient approximation for solids in our DFT calculations, we investigate both pure and yttrium-substituted HfO 2 . Our findings reveal an anomalous reduction in the 𝐶 33 component of the elastic tensor with increasing pressure, which becomes significant above 15 GPa and signals a potential pressure-driven structural phase transition at higher pressure. The analysis of atomic displacements under pressure sheds light on the unusual mechanical behavior and phase stability of this material. Additionally, we observe a transition from an indirect band gap to a direct band gap with increasing pressure, which could have significant implications for optical applications. Here, the effects of yttrium substitution on the mechanical and electronic properties are further examined, revealing that yttrium substitution softens the elastic response of this material and reduces the electronic band gap. These results enhance our understanding of elastic and mechanical responses of ferroelectric hafnia and its potential for applications in microelectronics, piezoelectric devices, and nonvolatile ferroelectric random-access memories. Further experimental validation is recommended to confirm our predictions and explore the practical implications of the observed phase transitions and electronic behavior of the ferroelectric hafnia under high-pressure conditions.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Multilayered luminescent solar concentrators based on engineered quantum dots
Luminescent solar concentrators (LSCs) based on engineered quantum dots (QDs) are disclosed that include at least one lower band-gap energy LSC layer and at least one higher band-gap energy LSC layer. The higher band-gap energy LSC layer has a higher internal quantum efficiency (IQE) than the lower band-gap energy LSC layer. The lower band-gap energy LSC layer may broadly absorb the remainder of the solar spectrum that is not absorbed by previous layers. An external optical efficiency (EQE) of at least 6%, and in some cases, more than 10%, may be achieved by such LSCs.
Source record↗
Theoretical study of intrinsic defects in cubic silicon carbide 3C-SiC
Using the local moment counter charge (LMCC) method to accurately represent the asymptotic electrostatic boundary conditions within density functional theory supercell calculations, we present a comprehensive analysis of the atomic structure and energy levels of point defects in cubic silicon carbide (3C-SiC). Finding that the classical long-range dielectric screening outside the supercell induced by a charged defect is a significant contributor to the total energy. we describe and validate a modified Jost screening model to evaluate this polarization energy. This leads to bulk-converged defect levels in finite size supercells. With the LMCC boundary conditions and a standard Perdew-Burke-Ernzerhof (PBE) exchange correlation functional, the computed defect level spectrum exhibits no band gap problem: the range of defect levels spans ~2.4 eV, an effective defect band gap that agrees with the experimental band gap. Comparing with previous literature, our LMCC-PBE defect results are in consistent agreement with the hybrid-exchange functional results of Oda et al. [J. Chem. Phys. 139, 124707 (2013)] rather than their PBE results. The difference with their PBE results is attributed to their use of a conventional jellium approximation rather than the more rigorous LMCC approach for handling charged supercell boundary conditions. The difference between standard dft and hybrid functional results for defect levels lies not in a band gap problem but rather in solving a boundary condition problem. The LMCC-PBE entirely mitigates the effect of the band gap problem on defect levels. The more computationally economical PBE enables a systematic exploration of 3C-SiC defects, where, most notably, we find that the silicon vacancy undergoes Jahn-Teller-induced distortions from the previously assumed T d symmetry, and that the divacancy, like the silicon vacancy, exhibits a site-shift bistability in p -type conditions.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Intermediate Bandgap (IB) Cu 3 VS x Se 4−x Nanocrystals as a New Class of Light Absorbing Semiconductors
A new family of highly uniform, cubic-shaped Cu 3 VS x Se 4−x (CVSSe; 0 ≤ x ≤ 4) nanocrystals based on earth-abundant materials with intermediate bandgaps (IB) in the visible range is reported, synthesized via a hot-injection method. The IB transitions and optical band gap of the novel CVSSe nanocrystals are investigated using ultraviolet-visible spectroscopy, revealing tunable band gaps that span the visible and near-infrared regimes. The composition-dependent relationships among the crystal phase, optical band gap, and photoluminescence properties of the novel IB semiconductors with progressive substitution of Se by S are examined in detail. High-resolution transmission electron microscopy and scanning electron microscopy characterization confirm the high crystallinity and uniform size (~19.7 nm × 17.2 nm for Cu 3 VS 4 ) of the cubic-shaped nanocrystals. Density functional theory (DFT) calculations based on virtual crystal approximation support the experimental findings, showing good agreement in lattice parameters and band gaps across the CVSSe series and lending confidence that the targeted phases and compositions have been successfully realized. A current conversion efficiency, i.e., incident photon-to-current efficiency, of 14.7% was achieved with the p-type IB semiconductor Cu 3 VS 4 . These novel p-type IB semiconductor nanocrystals hold promise for enabling thin film solar cells with efficiencies beyond the Shockley–Queisser limit by allowing sub-band-gap photon absorption through intermediate-band transitions, in addition to the conventional direct-band-gap transition.
Cu3VSxSe4−x↗
Nonunique fraction of Fock exchange for defects in two-dimensional materials
By investigating the vacancy and substitutional defects in monolayer WS 2 with hybrid functionals, we find that there is no unique amount of Fock exchange that concurrently satisfies the generalized Koopmans' condition and reproduces the band-gap and band-edge positions. Fixing the mixing parameter of Fock exchange based on the band gap can lead to qualitatively incorrect defect physics in two-dimensional materials. Instead, excellent agreement is achieved with both experiment and many-body perturbation theory within the GW approximation once the mixing parameters are tuned individually for the defect species and the band edges. Here, we show the departure from a unique optimized mixing parameter is inherent to two-dimensional systems as the band edges experience a reduced screening while the localized defects are subject to bulklike screening.
2-dimensional systems↗
Polymorphism and Phase Control in Dion–Jacobson 2D 3-(Aminomethyl)piperidinium-Based Metal Iodide Perovskites
Two-dimensional halide perovskites exhibit rich structural diversity and tunable optoelectronic properties, making them promising materials for energy, sensing, and photonic applications. In this work, we report the structural mapping of four distinct polymorphs, γ (P2 1 /c), β (P4/mbm), α (P4/mmm), and δ (Cmcm) in the two-dimensional iodoplumbate, iodostannate, and iodogermanate perovskite so-called Dion-Jacobson series (3AMP)MI4 (M = Sn, Pb, Ge), where 3AMP is 3-(aminomethyl)piperidinium. The phases exhibit systematic evolution in octahedral distortion, lattice symmetry, and metal–halide geometry, enabling structural control over optoelectronic properties. Notably, the α-phase of (3AMP)SnI 4 represents a rare, ambient-stable, high-symmetry structure for Sn-based perovskites, without a phase transition down to 100 K. Variable-temperature single-crystal diffraction, powder x-ray diffraction (PXRD), and calorimetry reveal metal- and temperature-dependent polymorph interconversions, including the emergence of long range supercell reflections in Pb-rich compositions at low temperature. Optical spectroscopy and photoelectron yield spectroscopy confirm band gap tunability and band alignment trends, highlighting symmetry-dependent shifts and anomalous band gap bowing in mixed-metal systems, verified by electronic structure calculations. Calculations additionally indicate that the higher symmetry phases have reduced electron and hole effective masses compared to the lower symmetry phases.
36 MATERIALS SCIENCE↗
Second-order nonlinear optical and linear ultraviolet-visible absorption properties of the type-II multiferroic candidates RbFe( A O 4 ) 2 ( A = Mo, Se, S)
Motivated by the search for type-II multiferroics, in this work, we present a comprehensive optical study of a complex oxide family of type-II multiferroic candidates: RbFe(MoO 4 ) 2 , RbFe(SeO 4 ) 2 , and RbFe(SO 4 ) 2 .We employ rotationalanisotropy second harmonic generation spectroscopy (RA SHG), a technique sensitive to point symmetries, to address discrepancies in literature-assigned point/space groups and to identify the correct crystal structures. At room temperature we find that our RA SHG patterns rotate away from the crystal axes in RbFe(AO 4 ) 2 ( A = Se, S), which identifies the lack of mirror symmetry and in-plane two-fold rotational symmetry. Also, the SHG efficiency of RbFe(SeO 4 ) 2 is two orders of magnitude stronger than RbFe(AO 4 )2 ( A = Mo, S), which suggests broken inversion symmetry. Additionally, we present temperature-dependent linear optical characterizations near the band edge of this family of materials using ultraviolet-visible absorption spectroscopy. Included is experimental evidence of the band gap energy and band gap transition type for this family. Subband gap absorption is also presented, which reveals prominent optical transitions, some with an unusual central energy temperature dependence. Furthermore, we find that by substituting the A site in RbFe(AO 4 ) 2 ( A = Mo, Se, S), the aforementioned transitions are spectrally tunable. Finally, we discuss the potential origin and impact of these tunable transitions.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗