Search Results (35)

In this study, we aim to enhance the internal quantum efficiency (IQE) of AlGaN-based ultraviolet (UV) light-emitting diodes (LEDs) by using the short-period AlGaN/GaN superlattice as a tunnel junction (TJ) to construct polarized structures. We analyze in detail the effect of this polarized TJ on the carrier injection efficiency and investigate the increase in hole and electron density caused by the formation of 2D hole gas (2DHG) and 2D electron gas (2DEG) in the superlattice structure. In addition, a dielectric layer is introduced to evaluate the effect of stress changes on the tunneling probability and current spread in TJ. At a current of 140 mA, this method demonstrates effective current expansion. Our results not only improve the performance of UV LEDs but also provide an important theoretical and experimental basis for future research on UV LEDs based on superlattice TJ. In addition, our study also highlights the key role of group III nitride materials in achieving efficient UV luminescence, and the polarization characteristics and band structure of these materials are critical for optimizing carrier injection and recombination processes. Full article

This review describes the development history of group-III nitride light-emitting diodes (LEDs) for over 30 years, which has achieved brilliant achievements and changed people′s lifestyles. The development process of group-III nitride LEDs is the sum of challenges and solutions constantly encountered with shrinking size. Therefore, this paper uses these challenges and solutions as clues for review. It begins with reviewing the development of group-III nitride materials and substrates. On this basis, some key technological breakthroughs in the development of group-III nitride LEDs are reviewed, mainly including substrate pretreatment and p-type doping in material growth, the proposal of new device structures such as nano-LED and quantum dot (QD) LED, and the improvement in luminous efficiency, from the initial challenge of high-efficiency blue luminescence to current challenge of high-efficiency ultraviolet (UV) and red luminescence. Then, the development of micro-LEDs based on group-III nitride LEDs is reviewed in detail. As a new type of display device, micro-LED has drawn a great deal of attention and has become a research hotspot in the current international display area. Finally, based on micro-LEDs, the development trend of nano-LEDs is proposed, which is greener and energy-saving and is expected to become a new star in the future display field. Full article

Sapphire has various applications in photonics due to its broadband transparency, high-contrast index, and chemical and physical stability. Photonics integration on the sapphire platform has been proposed, along with potentially high-performance lasers made of group III–V materials. In parallel with developing active devices for photonics integration applications, in this work, silicon nitride optical waveguides on a sapphire substrate were analyzed using the commercial software Comsol Multiphysics in a spectral window of 800~2400 nm, covering the operating wavelengths of III–V lasers, which could be monolithically or hybridly integrated on the same substrate. A high confinement factor of ~90% near the single-mode limit was obtained, and a low bending loss of ~0.01 dB was effectively achieved with the bending radius reaching 90 μm, 70 μm, and 40 μm for wavelengths of 2000 nm, 1550 nm, and 850 nm, respectively. Furthermore, the use of a pedestal structure or a SiO₂ bottom cladding layer has shown potential to further reduce bending losses. The introduction of a SiO₂ bottom cladding layer effectively eliminates the influence of the substrate’s larger refractive index, resulting in further improvement in waveguide performance. The platform enables tightly built waveguides and small bending radii with high field confinement and low propagation losses, showcasing silicon nitride waveguides on sapphire as promising passive components for the development of high-performance and cost-effective PICs. Full article

Group-III nitrides have transformed solid-state lighting and are strategically positioned to revolutionize high-power and high-frequency electronics. To drive this development forward, a deep understanding of fundamental material properties, such as charge carrier behavior, is essential and can also unveil new and unforeseen applications. This underscores the necessity for novel characterization tools to study group-III nitride materials and devices. The optical Hall effect (OHE) emerges as a contactless method for exploring the transport and electronic properties of semiconductor materials, simultaneously offering insights into their dielectric function. This non-destructive technique employs spectroscopic ellipsometry at long wavelengths in the presence of a magnetic field and provides quantitative information on the charge carrier density, sign, mobility, and effective mass of individual layers in multilayer structures and bulk materials. In this paper, we explore the use of terahertz (THz) OHE to study the charge carrier properties in group-III nitride heterostructures and bulk material. Examples include graded AlGaN channel high-electron-mobility transistor (HEMT) structures for high-linearity devices, highlighting the different grading profiles and their impact on the two-dimensional electron gas (2DEG) properties. Next, we demonstrate the sensitivity of the THz OHE to distinguish the 2DEG anisotropic mobility parameters in N-polar GaN/AlGaN HEMTs and show that this anisotropy is induced by the step-like surface morphology. Finally, we present the temperature-dependent results on the charge carrier properties of 2DEG and bulk electrons in GaN with a focus on the effective mass parameter and review the effective mass parameters reported in the literature. These studies showcase the capabilities of the THz OHE for advancing the understanding and development of group-III materials and devices. Full article

The present work focuses on the synthesis of a vanadium nitride (VN)/carbon nanocomposite material via the thermal decomposition of vanadyl phthalocyanine (VOPC). The morphology and chemical structure of the synthesized compounds were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), Fourier transformed infrared spectroscopy (FTIR), X-ray diffraction (XRD), and X-ray photoemission spectroscopy (XPS). The successful syntheses of the VOPC and non-metalated phthalocyanine (H₂PC) precursors were confirmed using FTIR and XRD. The VN particles present a needle-like morphology in the VN synthesized by the sol-gel method. The morphology of the VN/C composite material exhibited small clusters of VN particles. The XRD analysis of the thermally decomposed VOPC indicated a mixture of amorphous carbon and VN nanoparticles (VN(TD)) with a cubic structure in the space group FM-3M consistent with that of VN. The XPS results confirmed the presence of V(III)-N bonds in the resultant material, indicating the formation of a VN/C nanocomposite. The VN/C nanocomposite synthesized through thermal decomposition exhibited a high carbon content and a cluster-like distribution of VN particles. The VN/C nanocomposite was used as an anode material in LIBs, which delivered a specific capacity of 307 mAh g⁻¹ after 100 cycles and an excellent Coulombic efficiency of 99.8 at the 100th cycle. Full article

Highly indium-rich group-III nitrides are attracting attention for advancing our capacity to create highly effective optical emitters at extended visible/IR wavelengths or for enhancing bandgap engineering possibilities within the group-III nitride material framework. Current methods of synthesis are constrained in their efficacy, partially owing to the low decomposition temperature of indium nitride. Implementation of a new design of a vertical high-pressure spatial chemical vapor deposition (HPS-CVD) reactor with six separated precursor source zones and a rotating wafer carrier disk carrying four 2-inch wafers is proposed and analyzed using COMSOL Multiphysics as a commercial computational fluid dynamics (CFD) program to study the fluid phenomena inside the numerical domain. This study focuses on understanding the different flow patterns within the chambers at super-atmospheric conditions (5 atm to 30 atm) and identifying suitable operating conditions under which smooth and dominant vortex-free flow is achieved. Four 2-inch wafers are heated to maintain a temperature of 1200–1300 K at each pressure and gas type. Three different gas types (nitrogen, hydrogen, and ammonia) are used, and the impacts of different inlet flow velocities and rotational speeds are investigated and discussed. An operating matrix is presented for each analyzed system pressure providing suitable combinations of these operational variables for smooth flow in the chambers. Each gas type was identified to have a range of suitable rotational and inlet velocity regimes at each operating pressure. Overlap of these three gas-specific operating condition windows resulted in the identification of a generally suitable operating condition for smooth flow patterns in the system regardless of the gas type used, as required for the growth of group-III nitride materials. Full article

Indium nitride is an excellent semiconductor that belongs to the group of III nitride materials. Due to its unique properties, it is applied to various optoelectronic applications. However, its low thermal stability makes it difficult to synthesize. The present study introduces the synthesis of indium nitride nanoparticles, using ultrasound power (sonochemistry). The sonochemical method provides a low-cost and rapid technique for nanomaterial synthesis. InN nanoparticles were produced in only 3 h through the sonochemical reaction of InCl₃ and LiN₃. Xylene was used as a reaction solvent. X-ray powder diffraction (XRD) as well as high-resolution transmission electron microscopy (HRTEM) were adopted for the characterization of the obtained powder. According to our results, ultrasound contributed to the synthesis of InN nanocrystals in a cubic and a hexagonal phase. The obtained InN nanoparticles were further used to decorate titanium dioxide (TiO₂) by means of ultrasound. The contribution of InN nanoparticles on the processes of photocatalysis was investigated through the degradation of methylene blue (MB), a typical organic substance acting in place of an environment pollutant. According to the obtained results, InN nanoparticles improved the photocatalytic activity of TiO₂ by 41.8% compared with commercial micrometric titania. Full article

High indium-content group-III nitrides are of interest to further expand upon our ability to produce highly efficient optical emitters at longer visible/IR wavelengths or to broaden bandgap engineering opportunities in the group-III nitride material system. Current synthesis approaches are limited in their capabilities, in part due to the low decomposition temperature of indium nitride. A new high-pressure spatial chemical vapor deposition (HPS-CVD) has been proposed which can operate at pressures up to 100 atmospheres, thereby significantly raising the growth temperature of indium nitride more than 100 kelvins and permitting the investigation of the impact of pressure on precursor stability and reactivity. This study systematically analyzes an HPS-CVD reactor design using computational fluid dynamic modeling in order to understand favorable operating conditions for growth of group III nitrides. Specifically, the relationship between inlet gas type (nitrogen, hydrogen, or ammonia), inlet gas velocity, gas flow rate, and rotational speed of the wafer carrier is evaluated for conditions under which a smooth and dominant vortex-free flow are obtained over the wafer. Heater power was varied to maintain a wafer temperature of 1250–1300 K. Favorable operating conditions were identified that were simultaneously met for all three gas types, providing a stable operating window for a wide range of gas chemistries for growth; at one atmosphere, a disk rotational speed of 50 rpm and a flow rate of 12 slm for all gas types is desired. Full article

The combination of the unique physical properties of molybdenum disulfide (MoS₂) with those of gallium nitride (GaN) and related group-III nitride semiconductors have recently attracted increasing scientific interest for the realization of innovative electronic and optoelectronic devices. A deep understanding of MoS₂/GaN interface properties represents the key to properly tailor the electronic and optical behavior of devices based on this heterostructure. In this study, monolayer (1L) MoS₂ was grown on GaN-on-sapphire substrates by chemical vapor deposition (CVD) at 700 °C. The structural, chemical, vibrational, and light emission properties of the MoS₂/GaN heterostructure were investigated in detail by the combination of microscopic/spectroscopic techniques and ab initio calculations. XPS analyses on as-grown samples showed the formation of stoichiometric MoS₂. According to micro-Raman spectroscopy, monolayer MoS₂ domains on GaN exhibit an average n-type doping of (0.11 ± 0.12) × 10¹³ cm⁻² and a small tensile strain (ε ≈ 0.25%), whereas an intense light emission at 1.87 eV was revealed by PL analyses. Furthermore, a gap at the interface was shown by cross-sectional TEM analysis, confirming the van der Waals (vdW) bond between MoS₂ and GaN. Finally, density functional theory (DFT) calculations of the heterostructure were carried out, considering three different configurations of the interface, i.e., (i) an ideal Ga-terminated GaN surface, (ii) the passivation of Ga surface by a monolayer of oxygen (O), and (iii) the presence of an ultrathin Ga₂O₃ layer. This latter model predicts the formation of a vdW interface and a strong n-type doping of MoS₂, in closer agreement with the experimental observations. Full article

In this study, we present a theoretical study of the quantum spin Hall effect in InN/InGaN coupled multiple quantum wells with the individual well widths equal to two atomic monolayers. We consider triple and quadruple quantum wells in which the In content in the interwell barriers is greater than or equal to the In content in the external barriers. To calculate the electronic subbands in these nanostructures, we use the eight-band k∙p Hamiltonian, assuming that the effective spin–orbit interaction in InN is negative, which represents the worst-case scenario for achieving a two-dimensional topological insulator. For triple quantum wells, we find that when the In contents of the external and interwell barriers are the same and the widths of the internal barriers are equal to two monolayers, a topological insulator with a bulk energy gap of 0.25 meV can appear. Increasing the In content in the interwell barriers leads to a significant increase in the bulk energy gap of the topological insulator, reaching about 0.8 meV. In these structures, the topological insulator can be achieved when the In content in the external barriers is about 0.64, causing relatively low strain in quantum wells and making the epitaxial growth of these structures within the range of current technology. Using the effective 2D Hamiltonian, we study the edge states in strip structures containing topological triple quantum wells. We demonstrate that the opening of the gap in the spectrum of the edge states caused by decreasing the width of the strip has an oscillatory character regardless of whether the pseudospin-mixing elements of the effective Hamiltonian are omitted or taken into account. The strength of the finite size effect in these structures is several times smaller than that in HgTe/HgCdTe and InAs/GaSb/AlSb topological insulators. Therefore, its influence on the quantum spin Hall effect is negligible in strips with a width larger than 150 nm, unless the temperature at which electron transport is measured is less than 1 mK. In the case of quadruple quantum wells, we find the topological insulator phase only when the In content in the interwell barriers is larger than in the external barriers. We show that in these structures, a topological insulator with a bulk energy gap of 0.038 meV can be achieved when the In content in the external barriers is about 0.75. Since this value of the bulk energy gap is very small, quadruple quantum wells are less useful for realizing a measurable quantum spin Hall system, but they are still attractive for achieving a topological phase transition and a nonlocal topological semimetal phase. Full article

Powerful emitters of ultraviolet C (UVC) light in the wavelength range of 230–280 nm are necessary for the development of effective and safe optical disinfection technologies, highly sensitive optical spectroscopy and non-line-of-sight optical communication. This review considers UVC emitters with electron-beam pumping of heterostructures with quantum wells in an (Al,Ga)N material system. The important advantages of these emitters are the absence of the critical problem of p-type doping and the possibility of achieving record (up to several tens of watts for peak values) output optical power values in the UVC range. The review consistently considers about a decade of world experience in the implementation of various UV emitters with various types of thermionic, field-emission, and plasma-cathode electron guns (sources) used to excite various designs of active (light-emitting) regions in heterostructures with quantum wells of Al_xGa_1−xN/Al_yGa_1−yN (x = 0–0.5, y = 0.6–1), fabricated either by metal-organic chemical vapor deposition or by plasma-activated molecular beam epitaxy. Special attention is paid to the production of heterostructures with multiple quantum wells/two-dimensional (2D) quantum disks of GaN/AlN with a monolayer’s (1 ML~0.25 nm) thickness, which ensures a high internal quantum efficiency of radiative recombination in the UVC range, low elastic stresses in heterostructures, and high-output UVC-optical powers. Full article

Catalyst-free growth of III-V and III-nitride nanowires (NWs) by the self-induced nucleation mechanism or selective area growth (SAG) on different substrates, including Si, show great promise for monolithic integration of III-V optoelectronics with Si electronic platform. The morphological design of NW ensembles requires advanced growth modeling, which is much less developed for catalyst-free NWs compared to vapor–liquid–solid (VLS) NWs of the same materials. Herein, we present an empirical approach for modeling simultaneous axial and radial growths of untapered catalyst-free III-V NWs and compare it to the rigorous approach based on the stationary diffusion equations for different populations of group III adatoms. We study in detail the step flow occurring simultaneously on the NW sidewalls and top and derive the general laws governing the evolution of NW length and radius versus the growth parameters. The rigorous approach is reduced to the empirical equations in particular cases. A good correlation of the model with the data on the growth kinetics of SAG GaAs NWs and self-induced GaN NWs obtained by different epitaxy techniques is demonstrated. Overall, the developed theory provides a basis for the growth modeling of catalyst-free NWs and can be further extended to more complex NW morphologies. Full article

ScAlMgO₄ (SAM) is a promising substrate material for group III-nitride semiconductors. SAM has a lower lattice mismatch with III-nitride materials compared to conventionally used sapphire (Al₂O₃) and silicon substrates. Bulk SAM substrate has the issues of high cost and lack of large area substrates. Utilizing solid-phase epitaxy to transform an amorphous SAM on a sapphire substrate into a crystalline form is a cost-efficient and scalable approach. Amorphous SAM layers were deposited on 0001-oriented Al₂O₃ by sputtering and crystallized by annealing at a temperature greater than 850 °C. Annealing under suboptimal annealing conditions results in a larger volume fraction of a competing spinel phase (MgAl₂O₄) exhibiting themselves as crystal facets on the subsequently grown InGaN layers during MOCVD growth. InGaN on SAM layers demonstrated both a higher intensity and emission redshift compared to the co-loaded InGaN on GaN on sapphire samples, providing a promising prospect for achieving efficient longer-wavelength emitters. Full article

Despite III-nitride and silicon carbide being the materials of choice for a wide range of applications, theoretical studies on their quaternary alloys are limited. Here, we report a systematic computational study on the electronic structural properties of (SiC)_x (AlN)_1−x and (SiC)_x (AlN)_1−x quaternary alloys, based on state-of-the-art first-principles evolutionary algorithms. Trigonal (SiCAlN, space group P3m1) and orthorhombic (SiCGaN, space group Pmn2₁) crystal phases were as predicted for x = 0.5. SiCAlN showed relatively weak thermodynamic instability, while that of SiCGaN was slightly elevated, rendering them both dynamically and mechanically stable at ambient pressure. Our calculations revealed that the Pm31 crystal has high elastic constants, (C₁₁~458 GPa and C₃₃~447 GPa), a large bulk modulus (B₀~210 GPa), and large Young’s modulus (E~364 GPa), and our results suggest that SiCAlN is potentially a hard material, with a Vickers hardness of 21 GPa. Accurate electronic structures of SiCAlN and SiCGaN were calculated using the Tran–Blaha modified Becke–Johnson semi-local exchange potential. Specifically, we found evidence that SiCGaN has a very wide direct bandgap of 3.80 eV, while that of SiCAlN was indirect at 4.6 eV. Finally, for the quaternary alloys, a relatively large optical bandgap bowing of ~3 eV was found for SiCGaN, and a strong optical bandgap bowing of 0.9 eV was found for SiCAlN. Full article

We provide a systematic overview of the mechanochemical reactions of inorganic solids, notably simple binary compounds, such as oxides, nitrides, carbides, sulphides, phosphides, hydrides, borides, borane derivatives, and related systems. Whereas the solid state has been traditionally considered to be of little synthetic value by the broader community of synthetic chemists, the solid-state community, and in particular researchers focusing on the reactions of inorganic materials, have thrived in building a rich and dynamic research field based on mechanically-driven transformations of inorganic substances typically seen as inert and high-melting. This review provides an insight into the chemical richness of such mechanochemical reactions and, at the same time, offers their tentative categorisation based on transformation type, resulting in seven distinct groupings: (i) the formation of adducts, (ii) the reactions of dehydration; (iii) oxidation–reduction (redox) reactions; (iv) metathesis (or exchange) reactions; (v) doping and structural rearrangements, including reactions involving the reaction vessel (the milling jar); (vi) acid–base reactions, and (vii) other, mixed type reactions. At the same time, we offer a parallel description of inorganic mechanochemical reactions depending on the reaction conditions, as those that: (i) take place under mild conditions (e.g., manual grinding using a mortar and a pestle); (ii) proceed gradually under mechanical milling; (iii) are self-sustained and initiated by mechanical milling, i.e., mechanically induced self-propagating reactions (MSRs); and (iv) proceed only via harsh grinding and are a result of chemical reactivity under strongly non-equilibrium conditions. By elaborating on typical examples and general principles in the mechanochemistry of hard and high-melting substances, this review provides a suitable complement to the existing literature, focusing on the properties and mechanochemical reactions of inorganic solids, such as nanomaterials and catalysts. Full article