GaN Monolayer Research Articles

Influence of the electric field on the electronic structure of flat hexagonal two-dimensional GaN bilayers

Two-dimensional gallium nitride materials have recently garnered significant attention due to their promising optoelectronic properties, chemical stability, and mechanical strength. These attributes make them attractive for various technological applications, particularly optoelectronics, photonics, sensors, and more recently for high-power electronic applications. Our research, using first-principles calculations based on density functional theory (DFT) considering different exchange–correlation functionals, including van der Waals interaction, investigated the electronic properties of a single GaN monolayer and five different stacking configurations of GaN bilayers. The aim is to characterize the electronic properties of 2D-GaN-based materials and explore the impact of external electric fields on the bilayer stacking bandgap. We report the energetically most favorable among the bilayer configurations analyzed. Additionally, we confirmed that it is possible to modulate the energy bandgap both by the type of bilayer stacking and by the effect of the electric field. The ability to tune the energy bandgap (Eg) in 2D-GaN-based materials by adjusting their geometric configuration or applying an external electric field could inspire new applications in various technological fields.

Advantages of Ultrathin AlN/GaN/AlN Quantum Wells for Excitonic Population Distribution and Transition Features Studied by Phononic–Excitonic–Radiative Model

Excitons are expected to be a high‐efficiency emission source in UV light‐emitting devices. However, the damping of the excitonic laser oscillation has been reported under conditions where the excitonic states are expected to be populated in the conventional theory. In order to understand the exciton dynamics under the thermal nonequilibrium state, a theoretical model including various energy species in semiconductors such as electrons, phonons, and photons is required. Herein, a 2D phononic–excitonic–radiative model is constructed to analyze the exciton dynamics in a 2D system. 2D excitons with four principal quantum number states and the continuum in the lowest energy level of the AlN/GaN/AlN quantum wells are considered. It is found that the 2D phonon significantly augments the excitation transition rate. When the high recombination rate corresponding to stimulated emission is considered, the exciton binding energy of 108 meV is not enough to reduce the population in the high‐order discreet states and the continuum states, while the binding energy of 215 meV corresponding to the one monolayer GaN has an advantage of reducing these populations. The analysis of population flux has an advantage in discussing the increase in the kinetic energy transfer to the 1S exciton.

Study of vacancy defect in 2D/3D semiconductor heterostructure based on monolayer WSe2 and GaN

2D/3D heterostructure have attracted considerable attention within the scientific community due to their superior electronic properties and extensive spectral absorption capabilities. However, structural defect is inevitably introduced during the synthesis of 2D materials, which can significantly alter their intrinsic physical properties. Hence, 2D/3D semiconductor heterostructure composed of monolayers of WSe2 and GaN are constructed using first-principles calculations in this study. The impact of vacancy defect on the geometrical, electronic, and optical properties of the WSe2/GaN heterostructure is then systematically explored. The electronic property reveals that the introduction of impurity levels by vacancy defect, as well as interlayer surface-suspended bonds, results in a reduced band gap. This modification enhances the transfer ability of electrons from the valence band to the conduction band. Optical characterization demonstrates that the heterostructure formed by WSe2 and GaN exhibits a broad absorption spectrum, spanning from the visible to ultraviolet region, indicating a dual-wavelength photoresponse. Furthermore, regarding absorption coefficient and reflectivity, the heterostructure containing vacancy defect displays superior optical performance compared to the pristine heterostructure across both the visible and ultraviolet regions. The electronic and optical properties of the heterostructure can be tuned through the introduction of vacancy defects. These theoretical findings are anticipated to offer a foundational framework for the design of ultraviolet photodetectors utilizing WSe2/GaN heterostructure.

CVD-Grown Monolayer MoS2 and GaN Thin Film Heterostructure for a Self-Powered and Bidirectional Photodetector with an Extended Active Spectrum.

Photodetector technology has evolved significantly over the years with the emergence of new active materials. However, there remain trade-offs between spectral sensitivity, operating energy, and, more recently, an ability to harbor additional features such as persistent photoconductivity and bidirectional photocurrents for new emerging application areas such as switchable light imaging and filter-less color discrimination. Here, we demonstrate a self-powered bidirectional photodetector based on molybdenum disulfide/gallium nitride (MoS2/GaN) epitaxial heterostructure. This fabricated detector exhibits self-powered functionality and achieves detection in two discrete wavelength bands: ultraviolet and visible. Notably, it attains a peak responsivity of 631 mAW-1 at a bias of 0V. The device's response to illumination at these two wavelengths is governed by distinct mechanisms, activated under applied bias conditions, thereby inducing a reversal in the polarity of the photocurrent. This work underscores the feasibility of self-powered and bidirectional photocurrent detection but also opens new vistas for technological advancements for future optoelectronic, neuromorphic, and sensing applications.

Strain engineering of electronic, mechanical, and optical properties of orthorhombic III–V group monolayers by first principles calculations

Using first principles calculations, we systematically investigated the effects of strain engineering on the electronic, mechanical, and optical properties of two-dimensional (2D) orthorhombic III–V group materials, including BN, BP, BAs, AlN, AlP, and GaN. It is shown that all the III–V orthorhombic monolayers exhibit excellent mechanical anisotropy for Young’s modulus, Shear modulus, and Poisson’s ratio, especially for the AlN and GaN monolayers. AlN, AlP, and GaN are predicted to be indirect bandgap semiconductors, with their bandgap of 0.70, 0.15, and 0.53 eV, respectively. And BN is demonstrated to be a direct bandgap semiconductor (0.63 eV). Under uniaxial tensile strains, their electronic structures have non-monotonic anisotropic variations and these monolayers can be effectively modulated from metal to semiconductor, experiencing indirect–direct bandgap transitions. In addition, all the orthorhombic III–V materials exhibit highly anisotropic light-harvesting performances and the optical absorbance can be efficiently tailored with tensile strains applied along a- and b-directions. The strong optical absorptions in the visible light regions suggested that AlN, BN, and GaN may be optically tunable 2D materials for component absorbance layers for solar cell applications. The excellent anisotropic and tunable electronic, mechanical, and optical performances indicate that the orthorhombic III–V monolayers are promising candidates for potential applications of optoelectronics and photovoltaics.

High-performance Schottky-barrier field-effect transistors based on two-dimensional GaN with Ag or Au contacts

The performance of two-dimensional (2D) monolayer GaN Schottky barrier field effect transistors (SBFETs) with four different metals (Ag, Au, Al, and Pt) as electrodes were studied by using ab initio simulations. The N-type Schottky contact is formed on Ag-GaN, Au-GaN, and Pt-GaN, characterized by electron Schottky barrier heights (SBH) of 0.6, 0.5, and 0.38 eV, respectively. Whereas, Al-GaN contact formed P-type Schottky contact with hole SBH of 1.42 eV. The 5.1 nm GaN SBFETs with four metal electrodes all could overcome the short-channel effect. Additionally, GaN SBFETs with Ag and Au electrodes have excellent performance, whose ON-currents are 1151.1 μA/μm and 1258.9 μA/μm, respectively. They could satisfy the demands of International Technology Roadmap for Semiconductors for high-performance transistor. Furthermore, research indicates that the device's current increases with increasing temperature. Notably, under the constant bias and gate voltage, the current is unaffected by temperature variations between the left and right electrodes.

Ab-initio study of strain-tunable g-GaN/BN nanoheterostructure for optoelectronic and photocatalytic applications.

Two-dimensional (2D) nanoheterostructures of materials, integrating various phase or materials into a single nanosheet have stimulated large-scale research interest for designing novel two dimensional devices. In contemporary analysis present work, we examined the structural and electronic properties of the isolated 2D BN and GaN monolayers. We have investigated the structural stability and optoelectronic and photocatalytic response of the g-GaN/BN nanoheterostructure along with its response to strain. Nanoheterostructure g-GaN/BN is predicted to be a direct bandgap semiconductor with wide gap of 4.45eV, whose value can be effectively modulated by applied strain ( , ranging from 4.55 ( = - 4%) to 3.58eV ( = 8%). We also discovered that the tensile strain of 8% can substantially tune the direct bandgap of nanoheterostructure to indirect band gap nature. Even more important, the biaxial tensile strain engineering accentuates an enhancement of optical absorption in the UV region, broadening the light harvesting of the g-GaN/BN nanoheterostructure with the shifting of first absorption peak from 4.64 ( = - 4%) to 3.71eV ( = 8%). Furthermore, strain-tuned band edge potentials arrangement perfectly fits the water reduction and oxidation redox potentials. Our findings portend that the g-GaN/BN nanoheterostructure has application in prospective nanoscale optoelectronic devices and photocatalytic hydrogen evolution system. First principles calculations in this study are performed using density functional theory. Generalized gradient approximation within PBEsol functional employed to address the electron-electron exchange-correlation effects. For avoiding periodic interactions between the layers, we have inserted a vacuum region of thickness 10Å in the z-direction. For ensuring the convergence accuracy of the computed results, convergence criteria of the iteration process is set to be 0.0001eV. Local modified Becke-Johnson, a semi local functional, is applied for calculating electronic and optical properties for more accuracy of results. As in layered 2D nanoheterostructure, a factual depiction of the van der Waals interactions cannot be provided by conventional DFT techniques. Accordingly, in order to incorporate these interactions, we had employed the dispersion correction method of Grimme's.

Tunable electronic structure and optical properties of GaN monolayer via substituted doping and strain

In this study, the stability, optical properties and electronic structure of transition metal (TM) (Cr, Mn, Fe) doped GaN monolayers is investigated within the first-principles calculation methods. Additionally, the influence of biaxial strain on the aforementioned system is explored. The results demonstrate that substitutional doping effectively adjusts the electronic structure of GaN monolayer, enhancing its performance. The TM-doped GaN monolayer structures exhibit strong dynamic stability: doping with Cr and Fe bring magnetic properties, while Mn doping results in a half-metallicity property. In terms of optical absorption, the GaN:Mn system exhibits significant absorption in the infrared region, while GaN:Cr and GaN:Fe systems show stronger absorption in the visible light and ultraviolet regions compared to the pristine GaN monolayer. Under the biaxial strain from −3% to +12%, with increments of 3%, the band gap types of GaN:Cr, GaN:Fe, and GaN:Mn systems undergo minimal changes, with gradual reduction in gap values. Meanwhile, the optical absorption of doped systems exhibits systematic growth and redshift, particularly evident in the infrared-visible-ultraviolet spectral regions for the GaN:Mn system. These results indicate the controllability and variability of two-dimensional GaN materials, providing new avenues for the potential use of GaN as a material for optoelectronic devices.

First-principles study of the effects of Li/Na/K doping and point defects on the magnetic and photocatalytic properties of monolayer GaN (0 0 1)

In the experimental preparation of monolayer GaN (0 0 1) by chemical-vapor deposition, H impurities inevitably remain, and the intrinsic defect VGa inevitably forms. In this research, generalized gradient approximation + U plane-wave ultrasoft pseudopotentials are computed using the density-functional theory framework. The effects of Li/Na/K doping and point defect (Hi-VGa) coexistence on the magnetic properties and photocatalytic properties of monolayer GaN (0 0 1) surfaces are investigated. Results show that the monolayer Ga34MN36 (M = Li/Na/K) (0 0 1) surfaces are magnetic, and the source of its magnetism is primarily the itinerant electrons of N2− ions. The monolayer Ga34MHiN36 (0 0 1) surfaces are relatively more stable, and the separation degree of carriers is better than the monolayer Ga34MN36 (0 0 1) surfaces. In particular, the monolayer Ga34LiHiN36 (0 0 1) surface has a large electric-dipole moment, strong carrier activity, strong absorption efficiency, and strong oxidation-reduction properties. Therefore, the monolayer Ga34LiHiN36 (0 0 1) surface is the most suitable photocatalyst.

Effect of strain on the electronic structure and optical spectra of two-dimensional monolayer GaN

The effect of compressive strain and tensile strain on the band structure and optical spectra of two-dimensional monolayer GaN has been investigated. Computations were performed within density functional-theory. The results show that tensile two-dimensional monolayer-GaN undergoes an indirect-to-direct transition, which makes the material suitable for light-emitting and laser diodes. The material of interest is found to exhibit different optical properties dependent on the strain. Besides, the absorption band becomes wider and the optical absorption coefficient is reduced negligibly by strain, making two-dimensional-GaN a good candidate for application in photovoltaics and flexible optoelectronics.

Tuning the electronic structure of GaN monolayer by the single-atom promotor for hydrogenation of CO2

The efficient and cost-effective conversion of captured CO2 into valuable chemicals has garnered significant attention, driving the exploration of catalysts for CO2 capture and conversion. Here, we investigated a series of GaN monolayers with single metal atoms (M@GaN, M = Cr, Mn, Fe, Co, Ni, Cu, Zn, Al, and In) using first-principles calculations and ab initio molecular dynamics (AIMD) simulations. We propose a novel approach to enhance CO2 activation performance by tuning the single atom promotor (SAP). Compared to pristine GaN sheet, Ni@GaN, Cu@GaN, and Zn@GaN are predicted to have higher activity for CO2 adsorption and activation, in which the CO2 chemisorption process is predicted to be exothermic (−0.36 to −0.46 eV) with the low barrier (0.21–0.28 eV). This improvement can be attributed to occupied electronic states near the Fermi level in the N atom connected to SAP in the M@GaN (M = Ni, Cu, and Zn), enabling a better match with the LUMO level of CO2. In addition, compared with the AlN monolayer with better CO2 capture capability, Ni@GaN, and Zn@GaN exhibit considerable promise as catalysts for the hydrogenation of CO2 to HCOOH.

Theoretical investigation of fluorine-decorated gallium nitride monolayers with vacancy and doping defects

In this manuscript, through the formalism of density functional theory (DFT), we have investigated fluorine-decorated gallium nitride monolayers’ structural stability and electronic properties. We also have introduced vacancy and chemical substitution defects in the decorated structures to expand our investigation, since it is well-known that introducing these defects induces the appearance of notable electronic behaviors. Our results show that adding fluorine to the gallium nitride monolayer increases stability compared to the pristine GaN. In addition, it is possible to verify that the inserting defects in the GaN monolayer fluoride induce remarkable modifications in the energy gap values. Finally, we have shown that an essential property of GaN monolayer is that after fluorine adsorption, such nanostructures become more resistant to redox.

Confinement of Excitons within GaN 1D Nanoarchitectures Formed on AlN Molecular Steps

AbstractThe fabrication and the optical properties of ultrathin GaN quantum wells on AlN (0001) vicinal surfaces with macrosteps are studied. The employed growth condition spontaneously restricts the GaN thickness to one monolayer (ML) on a planar plane. However, because of a higher density of dangling bonds at macrosteps, 2 ML GaN can be stabilized only at step edges, which creates quantum‐wire‐like 1D nanostructures with a dimension of a few nanometers for the lateral confinement. Exciton (carrier) confinement within the 1D GaN nanostructure is predicted theoretically and is confirmed experimentally by strongly polarized photoluminescence with in‐plane twofold symmetry at a wavelength of ≈250 nm at room temperature. This study demonstrates one path to realize quantum confinement within a fine nanoarchitecture composed of nitride semiconductors and might provide clues to the future creation of novel low‐dimensional nanostructures for the UV–vis spectral range.

The Transition from Type-I to Type-II SiC/GaN Heterostructure with External Strain

Two-dimensional materials are widely used as a new generation of functional materials for photovoltaic, photocatalyst, and nano-power devices. Strain engineering is a popular method to tune the properties of two-dimensional materials so that performances can be improved or more applications can be obtained. In this work, a two-dimensional heterostructure is constructed from SiC and GaN monolayers. Using first-principle calculations, the SiC/GaN heterostructure is stacked by a van der Waals interaction, acting as a semiconductor with an indirect bandgap of 3.331 eV. Importantly, the SiC/GaN heterostructure possesses a type-II band structure. Thus, the photogenerated electron and hole can be separated in the heterostructure as a potential photocatalyst for water splitting. Then, the external biaxial strain can decrease the bandgap of the SiC/GaN heterostructure. From pressure to tension, the SiC/GaN heterostructure realizes a transformation from a type-II to a type-I semiconductor. The strained SiC/GaN heterostructure also shows suitable band alignment to promote the redox of water splitting at pH 0 and 7. Moreover, the enhanced light-absorption properties further explain the SiC/GaN heterostructure’s potential as a photocatalyst and for nanoelectronics.

Exploring Monolayer GaN Doped with Transition Metals: Insights from First-Principles Studies

Exploring Monolayer GaN Doped with Transition Metals: Insights from First-Principles Studies

A novel two-dimensional GaN/InGaN heterostructure for photocatalytic water splitting: A first-principles calculation

The pursuit of optimal bandgap and band edge positions is crucial for effective photocatalytic catalysts, leading to significant attentions in both experimental and theoretical research on modulating the band structure of semiconductor photocatalysts. In this study, the electronic, optical and photocatalytic properties of 2D monolayer GaN and GaN/InGaN heterostructures are investigated using DFT calculations. It reveals that introducing strain is an effective approach to not only alter the band gap type from indirect to direct but also influence the magnitude of the band gap. At a 10% tensile strain, a Z-type heterostructure is formed for the 2D GaN/InGaN heterostructures, which proves favorable for enhancing the efficiency of photocatalytic water splitting. However, it is worth noting that the band gap type remains indirect, necessitating additional energy for electron transitions. On the other hand, when increasing the compressive strain from − 2.5% to − 5%, the 2D GaN/InGaN heterostructure transforms from type I to type II, exhibiting direct band gaps with an enhanced light absorption range. This results in a significant redshift and increased optical absorption intensity within the visible light range, leading to a substantial enhancement in photocatalytic efficiency. Consequently, our findings demonstrate that the 2D GaN/InGaN heterostructure holds promising potential as a candidate material for efficient photocatalytic water splitting applications.

GaN/graphene heterostructures as promising anode materials for Li-ion batteries

In this research, the properties of GaN monolayer, defective GaN monolayer with N vacancies (GaN-VN), and van der Waals (vdW) heterostructures composed of them and graphene (GaN/graphene, GaN-VN/graphene) are systematically investigated using density functional theory (DFT), which includes assessment of the structure's stability, mechanical property, electronic structure analysis, lithium adsorption and diffusion properties, maximum theoretical capacity, and average open-circuit voltage. The calculations show that two-dimensional GaN transforms from semiconductor to metal by forming nitrogen-vacancy defects. This increases lithium adsorption performance while ensuring rapid electron motion in the electrode during lithium adsorption and removal processes. The synergistic effect between the heterostructure layers and the presence of the built-in electric field improves the electron and ion conductivity and lowers the migration energy barriers. In addition, the maximum theoretical capacities of defective GaN-VN, GaN/graphene, and GaN-VN/graphene can reach 970 mAh/g, 884 mAh/g, and 890 mAh/g, respectively, far exceeding those of the conventional graphite anode material (372 mAh/g). The above advantages indicate that defective GaN-VN, GaN/graphene, and GaN-VN/graphene are potential replacements for lithium-ion battery anodes.

The electronic, magnetic and optical properties of GaN monolayer doped with rare-earth elements

Structural, electronic, magnetic, and optical properties of rare earth (RE) metal element doped GaN monolayers are investigated using density functional theory, where RE = Nd, Sm, Eu, Gd, and Er. The introduction of RE atoms causes structural deformation of the GaN monolayer. The induced local magnetic moments are observed to be 4.00, 6.00, 7.00, 8.00, and 2.00 μB in Nd, Sm, Eu, Gd, and Er adsorbed GaN monolayers, respectively, while the values are 3.00, 5.00, 6.00, 7.00, and 3.00 μB in the substitution of Ga atoms. When Nd, Gd and Er adsorbed in GaN monolayer Fermi levels are shifted to the conduction band leading to metallicity, while in the case of Sm and Eu adsorption impurity states are found near the Fermi level. On the contrary, Eu, Gd and Er substitution of Ga atoms leads to the Fermi energy level being shifted below the VBM. In the Nd and Eu substitution system, the f-state is found near the Fermi level and the Nd-f state crosses the Fermi level. Optical absorption, transmission and refraction coefficients show that the addition of RE atoms can significantly enhance the prospects of GAN monolayers in visible as well as infrared applications. This research provides an outlook for the development of GaN monolayer-based optoelectronic as well as spintronics devices.

Many-Body Calculations of Excitons in Two-Dimensional GaN

We present an ab initio study on quasiparticle (QP) excitations and excitonic effects in two-dimensional (2D) GaN based on density-functional theory and many-body perturbation theory. We calculate the QP band structure using GW approximation, which generates an indirect band gap of 4.83 eV (K→Γ) for 2D GaN, opening up 1.24 eV with respect to its bulk counterpart. It is shown that the success of plasmon-pole approximation in treating the 2D material benefits considerably from error cancellation. On the other hand, much better gaps, comparable to GW ones, could be obtained by correcting the Kohn–Sham gap with a derivative discontinuity of the exchange–correlation functional at much lower computational cost. To evaluate excitonic effects, we solve the Bethe–Salpeter equation (BSE) starting from Kohn–Sham eigenvalues with a scissors operator to open the single-particle gap. This approach yields an exciton binding energy of 1.23 eV in 2D GaN, which is in good agreement with the highly demanding GW-BSE results. The enhanced excitonic effects due to reduced dimensionality are discussed by comparing the optical spectra from BSE calculations with that by random-phase approximation (RPA) for both the monolayer and bulk GaN in wurtzite phase. Additionally, we find that the spin–orbit splitting of excitonic peaks is noticeable in 2D GaN but buried in the bulk crystal.

The unexpected magnetism in 2D group-IV-doped GaN for spintronic applications

In this study, we systematically investigated the structural and magnetic properties of group-IV-doped monolayer GaN by first-principles calculations. Among the group-IV element, only Ge and Sn atoms with large atomic radii can form a buckling substituted doping structure with an in-plane magnetic moment of 1 μB per dopant. The compressive strains enhance the in-plane magnetic anisotropy, while tensile strains tend to destroy the magnetic moment of dopants. Both Ge and Sn atoms can stay on the same side of monolayer GaN to form anti-ferromagnetic semiconductors due to the large diffusion barrier for crossing to the monolayer GaN. The intrinsic Ga or N vacancies will eliminate the magnetic moments of group-IV dopants due to the charge transferring from the dopants to intrinsic vacancies. The N-rich growth conditions and a plentiful supply of Ge or Sn dopants to fill the intrinsic vacancies help to maintain the magnetic properties of group-IV-doped monolayer GaN.