InGaN Composition Research Articles

Thermoelectric properties of InGaN/GaN superlattices structure with high indium composition quantum dots

High indium composition InGaN is a promising material for thermoelectric harvesting application, which can work at high temperature and extreme environments. Due to the strong composition segregation, high indium composition InGaN material usually forms localized quantum dots, which advantageously enhances the thermoelectric (TE) properties. In this research, the two-dimensional InGaN/GaN superlattices (SLs) structured TE material with high In composition of 35% quantum dots is first grown and characterized. Using open-circuit voltage measurement, the Seebeck coefficient (S) exhibits a high value of −571 μV/K. Analysis indicates this relatively high S value is related to the increased density of electron states near the Fermi level induced by the reduced dimensionality, resulting in a power factor of 11.83 × 10−4W/m·K2. The dense boundary between InGaN quantum dots also increases the interface phonon scattering, thereby suppressing the heat transportation and leading to a low thermal conductivity (k) value of 19.9 W/m·K. As a result, a TE figure of merit (ZT) value of 0.025 is demonstrated in the sample. This work first clarifies the impact of embedded quantum dots in InGaN/GaN SLs structure on TE properties. It is very conductive for the design and fabrication of low-dimensional GaN based TE device.

Impact of Local Composition on the Emission Spectra of InGaN Quantum-Dot LEDs.

A possible solution for the realization of high-efficiency visible light-emitting diodes (LEDs) exploits InGaN-quantum-dot-based active regions. However, the role of local composition fluctuations inside the quantum dots and their effect of the device characteristics have not yet been examined in sufficient detail. Here, we present numerical simulations of a quantum-dot structure restored from an experimental high-resolution transmission electron microscopy image. A single InGaN island with the size of ten nanometers and nonuniform indium content distribution is analyzed. A number of two- and three-dimensional models of the quantum dot are derived from the experimental image by a special numerical algorithm, which enables electromechanical, continuum k→·p→, and empirical tight-binding calculations, including emission spectra prediction. Effectiveness of continuous and atomistic approaches are compared, and the impact of InGaN composition fluctuations on the ground-state electron and hole wave functions and quantum dot emission spectrum is analyzed in detail. Finally, comparison of the predicted spectrum with the experimental one is performed to assess the applicability of various simulation approaches.

InGaN micro-light-emitting diodes monolithically grown on Si: achieving ultra-stable operation through polarization and strain engineering

Micro or submicron scale light-emitting diodes (µLEDs) have been extensively studied recently as the next-generation display technology. It is desired that µLEDs exhibit high stability and efficiency, submicron pixel size, and potential monolithic integration with Si-based complementary metal-oxide-semiconductor (CMOS) electronics. Achieving such µLEDs, however, has remained a daunting challenge. The polar nature of III-nitrides causes severe wavelength/color instability with varying carrier concentrations in the active region. The etching-induced surface damages and poor material quality of high indium composition InGaN quantum wells (QWs) severely deteriorate the performance of µLEDs, particularly those emitting in the green/red wavelength. Here we report, for the first time, µLEDs grown directly on Si with submicron lateral dimensions. The µLEDs feature ultra-stable, bright green emission with negligible quantum-confined Stark effect (QCSE). Detailed elemental mapping and numerical calculations show that the QCSE is screened by introducing polarization doping in the active region, which consists of InGaN/AlGaN QWs surrounded by an AlGaN/GaN shell with a negative Al composition gradient along the c-axis. In comparison with conventional GaN barriers, AlGaN barriers are shown to effectively compensate for the tensile strain within the active region, which significantly reduces the strain distribution and results in enhanced indium incorporation without compromising the material quality. This study provides new insights and a viable path for the design, fabrication, and integration of high-performance µLEDs on Si for a broad range of applications in on-chip optical communication and emerging augmented reality/mixed reality devices, and so on.

Wavelength tune of InGaN based blue LEDs by changing indium percentage and operational voltage variables

Abstract— blue light-emitting-diodes (LEDs) are special and different then the other LEDs due to their high-efficient lighting. They have large badgap energy. So gallium nitrides are mostly used during designing blue light. This application focus on the emission properties of a InGaN LED. The emission intensity, energy diagram, spectrum, and efficiency are calculated for an applied voltage. The indium and GaN composition in the blue LED can be varied to control the emission wavelength. In here, composition of InGaN and operational voltage values were varied to control wavelength. Effects of the different InGaN composition and different voltage values were given in results as comperehansively for 5 different simulations. This study is dissimalar than other wevelength studies due to used original parameter values and wavelength compared methods for many situations about InGaN percentage and volatage values. As a result of simulations, we can infer that the high In_x percentage in composition and high voltage makes wavelength gap of an blue LED larger.

Growth of highly relaxed InGaN pseudo-substrates over full 2-in. wafers

A highly relaxed InGaN buffer layer was demonstrated over a full two-inch c-plane sapphire substrate by metalorganic chemical vapor deposition. The InGaN buffer layer was grown on a 100 nm GaN decomposition stop layer with a 3 nm thick high indium composition InGaN underlayer. After thermal decomposition of the underlayer at 1000 °C, a 200 nm thick In0.04Ga0.96N buffer showed 85% biaxial relaxation measured by a high resolution x-ray diffraction reciprocal space map. When used as a pseudo-substrate for the regrowth of InGaN/InGaN multi-quantum wells, the sample showed a 75 nm red-shift in room temperature photoluminescence when compared to a co-loaded GaN template reference. The longer emission wavelength is associated with higher indium incorporation in the InGaN layers from the lessening of the compositional pulling effect caused by compressive strain. Using this technique, a simple red light emitting diode was demonstrated with an active layer growth temperature of 825 °C and a peak wavelength of 622 nm at a current density of 20 A cm−2. This work represents a unique method to relax a III-nitride based layer over a full substrate.

Nanoscale InN clusters and compositional inhomogeneities in InGaN epitaxial layers quantified by tip-enhanced Raman scattering

We investigate the compositional homogeneity of InGaN thin films with a high In content grown by migration-enhanced plasma-assisted metal-organic chemical vapor deposition. Micro-Raman spectroscopy and tip-enhanced Raman spectroscopy (TERS) are used to analyze the local InGaN composition on the micro- and nanoscale. Based on conventional micro-Raman mapping, the InGaN composition for all samples appears uniform but shows indications for intrinsic phase separations. TERS, a nanoscopic technique with a high spatial resolution far below the diffraction limit, verifies the formation of nanoscale compositional inhomogeneities. The dimensions of these compositional fluctuations observed in TERS are confirmed by scattering-type scanning near-field infrared nanoscopy (s-SNIN). In contrast to s-SNIN, we show that TERS furthermore enables the quantification of the In content in the different compositional regions and even allows the identification of InN nanoclusters near the surface of the epitaxial films.

Impact of growth conditions and strain on indium incorporation in non-polar m-plane (101¯) InGaN grown by plasma-assisted molecular beam epitaxy

We establish the relationships between growth conditions, strain state, optical and structural properties of nonpolar m-plane (101¯0) InGaN with indium composition up to 39% grown by plasma-assisted molecular beam epitaxy. We find that indium mole fraction as a function of growth temperature can be explained by an Arrhenius dependence of InN decomposition only for high temperature and low indium composition InGaN films. For the samples following the Arrhenius behavior, we estimate the effective activation energy for InN thermal decomposition in m-plane InGaN to be about 1 eV. This value is approximately a factor of two smaller than that reported for c-plane InGaN films. At low growth temperatures, InGaN layers show less efficient indium incorporation than predicted by Arrhenius behavior. We attribute the lower than expected indium composition at low temperatures to the strain-induced compositional pulling effect. We demonstrate that at 540 °C, the increase in the InGaN layer thickness leads to a preferential strain relaxation along the a-direction and an increase in the indium composition. For the indium mole fraction up to x ∼ 0.16, 30-nm-thick m-plane InGaN layers can be coherently grown on GaN with smooth morphology and pronounced low-temperature photoluminescence indicating that the material quality is suitable for device applications.

Deep‐Level Defects and Impurities in InGaN Alloys

In this study, density functional theory calculations with a hybrid functional are used to examine the charge‐state transition levels of native point defects and impurities in InGaN alloys, with the goal of identifying centers that play a role in defect‐assisted recombination. Explicit alloy calculations are used to monitor the dependence of defect levels on indium content and distribution of In atoms. The relative shift (or lack thereof) of the charge‐state transition levels of the different defects is explained by the atomic character of the defect state and whether it is derived from valence‐band or conduction‐band states of the host material or acts as an atomic‐like impurity. The various possible atomic configurations of In and Ga cations for a given composition of InGaN lead to a distribution of charge‐state transition levels. Defects on the nitrogen site lead to a larger spread in levels compared with defects on the cation site.

Spatial Surface Charge Engineering for Electrochemical Electrodes

We introduce a novel concept for the design of functional surfaces of materials: Spatial surface charge engineering. We exploit the concept for an all-solid-state, epitaxial InN/InGaN-on-Si reference electrode to replace the inconvenient liquid-filled reference electrodes, such as Ag/AgCl. Reference electrodes are universal components of electrochemical sensors, ubiquitous in electrochemistry to set a constant potential. For subtle interrelation of structure design, surface morphology and the unique surface charge properties of InGaN, the reference electrode has less than 10 mV/decade sensitivity over a wide concentration range, evaluated for KCl aqueous solutions and less than 2 mV/hour long-time drift over 12 hours. Key is a nanoscale charge balanced surface for the right InGaN composition, InN amount and InGaN surface morphology, depending on growth conditions and layer thickness, which is underpinned by the surface potential measured by Kelvin probe force microscopy. When paired with the InN/InGaN quantum dot sensing electrode with super-Nernstian sensitivity, where only structure design and surface morphology are changed, this completes an all-InGaN-based electrochemical sensor with unprecedented performance.

Investigation of high indium-composition InGaN/GaN heterostructures on ZnO grown by metallic organic chemical vapor deposition

The optical properties and film quality for a series of high-In composition InGaN films grown on ZnO substrate by metal-organic chemical vapor deposition (MOCVD) are characterized by using high resolution X-ray diffraction (HRXRD), Rutherford backscattering (RBS), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL), and Raman scattering spectroscopy (RSS). The In composition is evaluated by analyzing the RBS and PL emission spectra. The XPS measurements revealed the diffusion of Zn atoms from the substrate into InGaN films. All the analyses of experimental measurements have shown that the growth temperature played an important role in indium composition as well as of film quality. An optimum growth temperature is a necessary condition for obtaining high-quality films.

InGaN気相成長における気相-固相関係に対する基板拘束の影響( ナノ構造・エピ成長分科会特集「窒化物半導体エピタキシャル成長における基板の役割」の再考)

InGaN気相成長における気相-固相関係に対する基板拘束の影響( ナノ構造・エピ成長分科会特集「窒化物半導体エピタキシャル成長における基板の役割」の再考)

Blue-Green-Red Emission From the InGaN/GaN Heterostructures Grown By Metal Organic Chemical Vapour Deposition

In the present investigation, InGaN layers were grown for three different growth duration on c-plane sapphire substrate using metal organic chemical vapour deposition (MOCVD). The thickness and In composition of the InGaN layers were determined by High Resolution X-Ray Diffraction (HRXRD). From the HRXRD simulation fit the composition and thickness of InGaN was found to be around 16% and 20-50 nm respectively. InGaN-related blue-green emission between 439-548 nm which are assigned to quasi-quantum dots as well as the InGaN matrix respectively. Emission at 657 nm reveals red emission assigned to the exciton localization. The blue- green-red emissions originate from the spinodal decomposition of the InGaN layers. Atomic Force Microscopy shows that the surface roughness increase and then decrease with increase in thickness of InGaN layer. Hall Effect measurements indicate high mobili ty attained in InGaN layer grown at optimized conditions with the semiconducting behavior.

Quantitative compositional analysis of InxGa1−xN/GaN multiquantum wells in light-emitting diodes

Abstract

Mobility limited by cluster scattering in ternary alloy quantum wires

The mobility limited by cluster scattering in ternary alloy semiconductor quantum wire (QWR) is theoretically investigated under Born approximation. We calculate the screened mobility due to clusters (high indium composition InGaN) scattering in the InxGa1−xN QWR structure. The characteristics of the cluster scattering mechanism are discussed in terms of the indium composition of clusters, the one-dimensional electron gas (1DEG) concentration, and the radius of QWR. We find that the density, breadth of cluster, and the correlation length have a strong effect on the electron mobility due to cluster scattering. Finally, a comparison of the cluster scattering is made with the alloy-disorder scattering. It is found that the cluster scattering acts as a significant scattering event to impact the resultant electron mobility in ternary alloy QWR.

Measuring composition in InGaN from HAADF-STEM images and studying the temperature dependence of Z-contrast

In this contribution, the indium concentration profile of an InxGa1−xN/GaN five-fold multi quantum well structure is measured from high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) images. The results are compared with an atom probe tomography study. Indium concentrations in the range of 26 at.% to 33 at.% are measured in the centre of the quantum wells. An additional indium layer of 14 at.% has been found on top of the quantum wells. In the second part, the temperature dependence of measured intensities in GaN is investigated. Here, multislice calculations in the frozen lattice approximation are carried out in dependence of specimen thickness and compared to experimental data. An increase of intensity with specimen temperature is found.

Mechanism of stress relaxation in (0001) InGaN/GaN via formation of V-shaped dislocation half-loops

From the analysis of available experimental data, we suggest a mechanism of stress relaxation in strained (0001) InGaN/GaN layers, assuming formation of V-shaped edge-type dislocation half-loops. An energy-balance approach is applied to estimate the critical thickness of the InGaN layer resulting in generation of the V-shaped half-loops. The computed dependence of the critical thickness on the InGaN composition agrees well with the literature data reported for single-layer InGaN/GaN heterostructures.

Marked suppression of In incorporation in heavily Si-doped InxGa1−xN (x ∼ 0.3) grown on GaN/α-Al2O3(0001) template

InxGa1−xN (x ∼ 0.3) films doped with Si up to 1022 cm−3 are grown on GaN/α-Al2O3(0001) templates by the metal-organic vapor phase epitaxy using monomethylsilane (MMSi) as a Si source. The In composition in InGaN is markedly decreased with increasing MMSi flow rate; In compositions are 0.32 and 0.12 for 0 and 4.3 μmol/min flow rates, respectively. The sum of concentrations of Si and In in InGaN is independent on MMSi flow rate and the Ga incorporation is not affected by the Si doping, suggesting that Si atoms are preferably incorporated into sites where In atoms should be incorporated.

Relationship of quantum-well potential profile and luminescence of InGaN/GaN heterostructures

Photoluminescence (PL) of a series of InGaN/GaN heterostructures with multiple quantum wells (QW) differing in their thicknesses and potential profiles that were grown by MOCVD on (0001) sapphire substrates was studied. Samples with varying InGaN composition within a QW layer that were obtained by varying the growth temperature demonstrated a considerably smaller PL spectral shift upon varying the excitation level, greater PL efficiency at low excitation levels, and slower radiative recombination times than samples grown at constant temperature. This was caused by a less pronounced quantum-confined Stark effect in QW of variable InGaN composition. It was established that varying the temperature during during InGaN QW layer growth resulted in higher heterogeneity of the InGaN composition, which was manifested in a higher degree of localization of photo-generated carriers.

Near-infrared InN quantum dots on high-In composition InGaN

We report the growth of InN quantum dots (QDs) on thick InGaN layers with high In composition (>50%) by molecular beam epitaxy. Optimized growth conditions are identified for the InGaN layers at reduced growth temperature and increased active N flux resulting in minimized phase separation and defect generation. The InN QDs grown on top of the optimized InGaN layer exhibit small size, high density, and photoluminescence up to room temperature. The InN/InGaN QDs reveal excellent potential for intermediate band solar cells with the InGaN and InN QD bandgap energies tuned to the best match of absorption to the solar spectrum.

Growth rate and composition of InGaN during InGaN/GaN quantum wells selective area metal-organic vapor phase epitaxy considering surface diffusion

Film growth rate and composition variation were numerically analyzed during the selective area growth of InGaN on both GaN triangular stripe and hexagonal pyramid microfacets. To obtain the In composition of the film, concentration of In and Ga atoms due to the surface diffusion was added to the concentration determined from the Laplace equation that governs the gas phase diffusion. When the surface diffusion is considered, the In composition and resulting wavelength increased compared to the results obtained from the vapor phase diffusion model. The In content also increased according to the increasing mask width.