group-III Nitrides Research Articles

Nanomaterial integration in micro LED technology: Enhancing efficiency and applications

The micro-light emitting diode (µLED) technology is poised to revolutionise display applications through the introduction of nanomaterials and Group III-nitride nanostructures. This review charts state-of-the-art in this important area of micro-LEDs by highlighting their key roles, progress and concerns. The review encompasses details from various types of nanomaterials to the complexity of gallium nitride (GaN) and III nitride nanostructures. The necessity to integrate nanomaterials with III-nitride structures to create effective displays that could disrupt industries was emphasised in this review. Commercialisation challenges and the economic enhancement of micro-LED integration into display applications using monolithic integrated devices have also been discussed. Furthermore, different approaches in micro-LED development are discussed from top-down and bottom-up approaches. The last part of the review focuses on nanomaterials employed in the production of micro-LED displays. It also highlights the combination of III-V LEDs with silicon LCDs and perovskite-based micro-LED displays. There is evidence that efficiency and performance have improved significantly since the inception of the use of nanomaterials in manufacturing these.

Growth and characterization of Mg-doped GaN and InGaN nanopillar-crystals based on steering-crystal-formed multi-crystalline Si substrates

In our past research, Group-III nitride nanopillar crystals were grown vertically on the multi-crystalline silicon substrate and applied to surface-emitting LEDs. To discuss the further possibilities of this kind of LEDs, such as application in long-wavelength LEDs, Mg-doped GaN and InGaN as important parts of the LEDs were grown under various conditions. Different testing experiments were carried out on these GaN-related samples to clarify their surface morphologies and luminescence characteristics. It was confirmed that Mg was successfully doped into GaN grown on the multi-crystalline silicon substrate. InGaN with a wide range of In-contents was obtained by using the same substrate. It is believed that these materials can be applied to various optoelectronic devices, especially large-area light-emitting devices with emissions of more colors, by analyzing the various properties.

High growth rate magnetron sputter epitaxy of GaN using a solid Ga target

Magnetron sputter epitaxy (MSE) is a promising processing route for group-III nitride semiconductors, with the potential to enable high-quality and low cost GaN growth for widespread use. However, fundamental technological hurdles must be overcome to enable the adoption of MSE in industrial production. Here, we present a new UHV-compatible magnetron design with high-performance cooling, enabling high GaN growth rates at high growth temperatures using a solid Ga target. The magnetron is tested with a wide range of process parameters and a stable process is feasible while maintaining the solid state of the Ga target. High GaN growth rates of up to 5 μm/h are achieved at room temperature and a growth rate of 4 μm/h at high temperature, which is one order of magnitude higher compared to MSE with a liquid target. We grow GaN on c-plane sapphire substrates and show the impact of partial pressure ratio and target-to-substrate distance (TSD) on growth rate, film morphology and crystal quality of GaN films with scanning electron microscopy and X-ray diffraction. While the growth rate and film morphology are strongly impacted by the process parameter variation, the crystal quality is further impacted by the overall film thickness. For a 2 μm thick GaN film a full width at half maximum of X-ray rocking curve (ω-FWHM) of GaN 10 1‾ 1 reflection of 0.32° is achieved. We demonstrate a process window for growth of dense and smooth GaN films with high crystal quality using low N2 flow rates and high TSD. By introducing a 20 nm AlN nucleation layer prior to the growth of 390 nm GaN, the ω-FWHM of GaN 0002 reflection of 0.19° is achieved. The epitaxially grown crystalline structure is precisely examined by transmission electron microscopy.

Design and analysis of a group-III nitride superlattice structure based semiconductor laser diode for blue region emission

The demand for high-power blue laser diodes (LDs) in the range above 2 W has been steadily increasing due to their applications in solid-state lighting, projection displays, high-density optical data storage and underwater communication. However, current designs face limitations in terms of achieving both high power output and efficiency. This work focuses on the design, development and numerical analysis of a blue LD utilizing group-III nitride superlattice structures. The present study aims to overcome design challenges by investigating the fundamental factors affecting the performance of blue LDs based on superlattice InGaN structures through careful device parameter optimization. The results show that our device successfully emits at around 430 nm wavelength and is capable of achieving a differential quantum efficiency of 46.91%, with a maximal optical power output of 2.18 W for 1.71 A of current for a strip width of 15 µm. However, when the strip width is increased to 20 µm, 4.6 W optical power is achieved with 3 A of injection current. Numerical studies are performed with several calibrated physics models and finite-difference time-domain techniques. Our results provide an insight into the potential of using superlattice group-III nitride structures to enhance the performance of blue LDs, opening up new possibilities for high-power and high-efficiency devices in the future.

Gas-phase study of the behavior of trimethyl gallium and triethyl gallium by optical emission spectroscopy and quadrupole mass spectroscopy for the growth of GaN by REMOCVD (radical-enhanced metalorganic chemical vapor deposition)

Metal-organic CVD (MOCVD) is a well-established means of epitaxial growth of III-nitrides in terms of production. To overcome the drawbacks of MOCVD, we have developed a radical-enhanced MOVCVD (REMOCVD) technique which is promising to grow group-III nitride materials at lower temperatures without ammonia gas. The gas phase behavior of trimethyl gallium (TMG) and triethyl gallium (TEG) in the chamber is studied with optical emission spectroscopy (OES) and quadrupole mass spectroscopy. From OES results, it is found that the parasitic reactions due to activated Ga and CN could be avoided by introducing hydrogen as a source gas together with nitrogen gas. The TEG is completely decomposed in REMOCVD at 550 °C which is a much lower temperature compared to TMG in a hydrogen atmosphere. Also, it is found that due to the low decomposition temperature of TEG, TEG contaminated the gas line which needs to be cleaned often.

Characterization of Ga-face/Ga-face and N-face/N-face interfaces with antiparallel polarizations fabricated by surface-activated bonding of freestanding GaN wafers

Electrical properties of heterojunctions of group-III nitrides are largely sensitive to interface charges due to the discontinuity of polarizations. By means of surface-activated bonding of double-side polished freestanding GaN (0001) wafers, we fabricate Ga-face/Ga-face and N-face/N-face interfaces with antiparallel spontaneous polarizations, i.e. interfaces with the greatest discontinuity of polarizations, to investigate their electrical and nanostructural properties. Built-in potential of N-face/N-face interface is smaller than that of Ga-face/Ga-face interface after a post-bonding annealing at 600 °C. The difference in built-in potentials between the two antiparallel polarized interfaces is analyzed in the framework of charge-neutrality-level model with effects of antiparallel polarizations incorporated, and the density of interface states is roughly estimated. The leak is enhanced in both Ga-face/Ga-face and N-face/N-face interfaces by annealing at higher temperatures. Contribution of defects observed in the vicinity of bonding interfaces is suggested.

Overcoming the Miscibility Gap of GaN/InN in MBE Growth of Cubic InxGa1-xN.

The lack of internal polarization fields in cubic group-III nitrides makes them promising arsenic-free contenders for next-generation high-performance electronic and optoelectronic applications. In particular, cubic InxGa1-xN semiconductor alloys promise band gap tuning across and beyond the visible spectrum, from the near-ultraviolet to the near-infrared. However, realization across the complete composition range has been deemed impossible due to a miscibility gap corresponding to the amber spectral range. In this study, we use plasma-assisted molecular beam epitaxy (PAMBE) to fabricate cubic InxGa1-xN films on c-GaN/AlN/3C-SiC/Si template substrates that overcome this challenge by careful adjustment of the growth conditions, conclusively closing the miscibility gap. X-ray diffraction reveals the composition, phase purity, and strain properties of the InxGa1-xN films. Scanning transmission electron microscopy reveals a CuPt-type ordering on the atomistic scale in highly alloyed films with x(In) ≈ 0.5. Layers with much lower and much higher indium content exhibit statistical distributions of the cations Ga and In. Notably, this CuPt-type ordering results in a spectrally narrower emission compared to that of statistically disordered zincblende materials. The emission energies of the films range from 3.24 to 0.69 eV and feature a quadratic bowing parameter of b = 2.4 eV. In contrast, the LO-like phonon modes that are observed by Raman spectroscopy exhibit a one-mode behavior and shift linearly from c-GaN to c-InN.

Comprehensive study of group III-nitride light emitting diode structures based on sapphire and ScAlMgO4 (0001) substrate for high intensity green emission

To mitigate the green gap problems existing in GaN/InGaN/AlGaN system on sapphire substrate, an In0.17Ga0.83N/InxGa1–xN/AlyGa1–yN based LED structure on ScAlMgO4 (0001) substrate has been introduced for green light (525…565 nm) emission. On ScAlMgO4 (0001) substrate, 35% of In composition with 1.6 nm well thickness and only 15% of Al composition with 1.1 nm thick AlGaN as capping layer on top provide the best LED structure. It provides minimum equivalent lattice mismatch (0.01%) with reasonable overall elastic energy value (0.47 J/m2). Most importantly, it provides at least 10% brighter green light emission than that of sapphire based LED structure.

Significant phonon drag effect in wide band gap GaN and AlN

Understanding the electrical and thermal transport properties of group-III nitride semiconductors is crucial for their electronic and thermoelectric applications. This study investigates the impact of the phonon drag effect, which refers to the momentum exchange between nonequilibrium phonons and electrons, on electronic transport in GaN and AlN. Results show that, even at room temperature, phonon drag significantly enhances mobility and the Seebeck coefficient. The study delves into the specific mechanisms for this.

Single-frequency violet and blue laser emission from AlGaInN photonic integrated circuit chips.

Chip-based, single-frequency and low phase-noise integrated photonic laser diodes emitting in the violet (412 nm) and blue (461 nm) regime are demonstrated. The GaN-based edge-emitting laser diodes were coupled to high-quality on-chip micro-resonators for optical feedback and mode selection resulting in laser self-injection locking with narrow emission linewidth. Multiple group III-nitride (III-N) based photonic integrated circuit chips with different waveguide designs including single-crystalline AlN, AlGaN, and GaN were developed and characterized. Single-frequency laser operation was demonstrated for all studied waveguide core materials. The best side-mode suppression ratio was determined to be ∼36 dB at 412 nm with a single-frequency laser emission linewidth of only 3.8 MHz at 461 nm. The performance metrics of this novel, to the best of our knowledge, type of laser suggest potential implementation in next-generation, portable quantum systems.

MOCVD of InGaN on ScAlMgO4 on Al2O3 Substrates with Improved Surface Morphology and Crystallinity

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.

Highly Uniform Array of Hexagonally Symmetric Micro‐Pyramid Structures for Scalable and Single Quantum Dot Emitters (Adv. Mater. Interfaces 8/2023)

Uniform Single Quantum Dot Emitters Controlling the position, size and shape of group III-nitride quantum dots is critical for the development of scalable single quantum emitters operable at room temperature. In article number 2202085, Yong-Hoon Cho and colleagues present a methodology for highly uniform, site-controlled GaN micro-pyramidal structures with a high degree of hexagonal symmetry by adjusting growth conditions under the self-limited growth mechanism. By successively growing a thin InGaN layer on the uniform pyramidal arrays with growth rate anisotropy, high-performance single photon emission from the apex of each pyramid can be achieved with suppressed background emission from side quantum wells of the pyramids.

Optical excitations of graphene-like materials: group III-nitrides.

By using first-principles calculations, we have studied the electronic and optical characteristics of group III-nitrides, such as BN, AlN, GaN, and InN monolayers. The optimized geometry, quasi-particle energy spectra, charge density distributions, band-decomposed charge densities, and Van Hove singularities in density of states are described in the work using physical and chemical pictures and orbital hybridizations found in B-N, Al-N, Ga-N, and In-N chemical bonds. Moreover, the dielectric functions, energy loss functions, absorption coefficients, and reflectance spectra with electron-hole interactions of optical properties are successfully achieved. More importantly, the close relations between electronic and optical properties are successfully demonstrated. The theoretical framework will be useful to research other graphene-like materials.

Study of group-III nitride semiconductor for novel neutron semiconducting detector

Study of group-III nitride semiconductor for novel neutron semiconducting detector

Density functional theory study of the sensing of ozone gas molecules by using fullerene-like Group-III nitride nanostructures

Recently, nanostructure-based gas sensors have drawn huge attention in this industrial era for environmental monitoring. We have performed DFT computations using B3LYP functional with6–31G Gaussian basis set to study the interaction of O3 molecules with B12N12, Al12N12, Ga12N12, AlB11N12, and GaB11N12 nanocages. To explore the sensing behavior, we have investigated structural properties, thermodynamic properties, electronic properties, dipole moment, and NBO charge transfer. The quantum theory of atoms in molecules (QTAIM) analysis displays that the interaction of O3 molecules with group-III nitride nanocages is a closed shell (non-covalent) type. The total density of state (DOS) graph shows that after adsorption the HOMO-LUMO band gap reduces in the significant range i.e. adsorption has a noteworthy influence on electronic properties. Therefore, AlB11N12, GaB11N12, and Al12N12 could be very promising in the field of sensing O3 molecules.

High performance inorganic filterless narrowband photodetectors

• A strategy based on bandpass response behavior is proposed for developing filterless narrowband photodetectors. • The bandpass response behavior realizes in full inorganic semiconductors. • The mechanism involved in filterless narrowband photodetector is clarified. The filterless narrowband photodetector is emergent in the field of optoelectric detection due to its spectral discrimination and avoiding interference from other bands. Distinguished from the presently developing strategy based on organic semiconductors, a strategy based on bandpass response behavior by constructing two kinds of group-III nitride semiconductors with different bandgap is proposed. Through functional verification of the prototype device, the results show that high performance filterless narrowband photodetector can be obtained by this strategy. Moreover, the full-width at half maximum and the response band of the bandpass response behavior can be adjusted by manipulating the alloy components.

Interlayer and Intralayer Excitons in AlN/WS2 Heterostructure

The study of intra and interlayer excitons in 2D semiconducting vdW heterostructures is a very hot topic not only from a fundamental but also an applicative point of view. Due to their strong light-matter interaction, Transition Metal Dichalcogenides (TMD) and group-III nitrides are particularly attractive in the field of opto-electronic applications such as photo-catalytic and photo-voltaic ultra-thin and flexible devices. Using first-principles ground and excited-state simulations, we investigate here the electronic and excitonic properties of a representative nitride/TMD heterobilayer, the AlN/WS2. We demonstrate that the band alignment is of type I, and low energy intralayer excitons are similar to those of a pristine WS2 monolayer. Further, we disentangle the role of strain and AlN dielectric screening on the electronic and optical gaps. These results, although they do not favor the possible use of AlN/WS2 in photo-catalysis, as envisaged in the previous literature, can boost the recently started experimental studies of 2D hexagonal aluminum nitride as a good low screening substrate for TMD-based electronic and opto-electronic devices. Importantly, our work shows how the inclusion of both spin-orbit and many-body interactions is compulsory for the correct prediction of the electronic and optical properties of TMD/nitride heterobilayers.

Examining Different Regimes of Ionization-Induced Damage in GaN Through Atomistic Simulations.

The widespread adoption of gGaN in radiation-hard semiconductor devices relies on a comprehensive understanding of its response to strongly ionizing radiation. Despite being widely acclaimed for its high radiation resistance, the exact effects induced by ionization are still hard to predict due to the complex phase-transition diagrams and defect creation-annihilation dynamics associated with group-III nitrides. Here, the Two-Temperature Model, Molecular Dynamics simulations and Transmission Electron Microscopy, are employed to study the interaction of Swift Heavy Ions with GaN at the atomic level. The simulations reveal a high propensity of GaN to recrystallize the region melted by the impinging ion leading to high thresholds for permanent track formation. Although the effect exists in all studied electronic energy loss regimes, its efficiency is reduced with increasing electronic energy loss, in particular when there is dissociation of the material and subsequent formation of N2 bubbles. The recrystallization is also hampered near the surface where voids and pits are prominent. The exceptional agreement between the simulated and experimental results establishes the applicability of the model to examine the entire electronic energy loss spectrum. Furthermore, the model supports an empirical relation between the interaction cross sections(namely for melting and amorphization) and the electronic energyloss.

Combined experimental and theoretical investigation of electronic properties of nitrides

A comprehensive study of the electronic structure of group-III nitrides (AlN, GaN, InN, and BN) crystallizing in the wurtzite, zinc-blende, and graphitelike hexagonal (BN) structures is presented. A large set of the x-ray emission and absorption spectra was collected at the several synchrotron radiation facilities at installations offering the highest possible energy resolution. By taking advantage of the linear polarization of the synchrotron radiation and making careful crystallographic orientation of the samples, the bonds along c axis (rr) and ‘‘in plane’’ (u) in the wurtzite structure could be separately examined. Particularly for AlN we found pronounced anisotropy of the studied bonds. The experimental spectra are compared directly with ab initio calculations of the partial density of states projected on the cation and anion atomic sites. For the GaN, AlN, and InN the agreement between structures observed in the calculated density of states (DOS) and structures observed in the experimental spectra is very good. In the case of hexagonal BN we have found an important influence of insufficient core screening in the x-ray spectra that influences the DOS distribution. The ionicity of the considered nitrides is also discussed.

Structural properties of group-III nitrides

We present first-principles calculations of structural and electronic properties of group-III nitrides in wurtzite and zinc-blende structure. For a most accurate treatment of these wide-band-gap semiconductors within local density approximation we employ our self-interaction- and relaxation-corrected pseudopotentials together with Gaussian-orbital basis sets. The results for BN, AlN, GaN, and InN are in good agreement with a host of experimental data yielding a consistent theoretical description of this class of technologically important semi- conductor compounds. [S0163-1829(97)05119-9]