High Al Composition Research Articles

Current transport mechanism of AlGaN-channel Schottky barrier diode with extremely low leakage current and high blocking voltage of 2.55 kV

This Letter presents work on lateral AlGaN-channel Schottky barrier diodes (SBDs) with impressive reverse blocking characteristics and low onset voltage (VON). A low reverse current (IR) of 28 nA/mm and low VON of 0.60 V are obtained by utilizing an AlGaN back barrier layer with high Al composition and low work function metal as the anode. The fabricated AlGaN-channel SBD with an anode–cathode distance (LAC) of 30 μm achieves a high blocking voltage of 2.55 kV and a power figure-of-merit of 363 MW/cm2. Meanwhile, the current transport mechanism of AlGaN-channel SBDs goes through thermionic emission, thermionic field emission, and trap-assisted tunneling as the reverse bias is gradually increased. The thermal activation energy (EA) is calculated to be 141.3 meV at high reverse bias. IR at 475 K is only 3 μA/mm, which shows an adequate barrier height for rectifying at high temperature even with low VON. The AlGaN-channel SBDs show great promise for next-generation power electronics with balanced forward and reverse characteristics.

AlN/Al0.5Ga0.5N HEMTs with heavily Si-doped degenerate GaN contacts prepared via pulsed sputtering

This paper reports AlN barrier Al0.5Ga0.5N high electron mobility transistors (HEMTs) with heavily Si-doped degenerate GaN contacts prepared by pulsed sputtering deposition. Selectively regrown n-type GaN contacts exhibit typical degenerate properties with the electron concentration and mobility of 2.6 × 1020 cm−3 and 115 cm2 V−1 s−1, respectively, resulting in a record low contact resistance R C of 0.43 Ω mm for the AlN/Al0.5Ga0.5N HEMTs. The AlN/Al0.5Ga0.5N HEMTs displayed a remarkable DC output characteristic with a maximum drain current density of 250 mA mm−1, a transconductance of 32 mS mm−1, and an On/Off ratio >106. The present results show potential overcoming challenges in ohmic contact formation for high-power and high-frequency AlGaN electron devices with high Al composition.

Influence of potassium hydroxide molarity and etching time on etching of Al-rich aluminium gallium nitride layer

In this work, n-doped AlGaN layer with a high Al composition of around 70% were etched using KOH solution. The molarity of KOH and the etching time were varied. With KOH molarity of 5 mol/L, no significant change in the formation of hexagonal pores, for 5 min etching and 10 min etching, was observed. Similar behaviour was also observed for the etching with 10 mol/L of KOH, which was carried out for 5 min. Nonetheless, with 10 mol/L of KOH, regardless of etching time, some of the Ga atoms were removed from the AlGaN lattice structure, resulting in AlGaN material with slightly higher Al composition. Besides, interestingly, bigger hexagonal pores (in macro scales) were formed when the etching was carried-out for 10 min using 10 mol/L of KOH. However, oxygen-containing materials were detected on the surface.

Surface Modification of AlGaN Solar-Blind Ultraviolet MSM Photodetectors With Octadecanethiol

We successfully fabricate the AlGaN solar-blind ultraviolet metal-semiconductor-metal (MSM) photodetectors (PDs) with high Al composition of 0.6, and an effective method by modifying organic molecules of Octadecanethiol (ODT) on Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.6</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.4</sub> N surface is proposed to enhance the optoelectronic performance of the MSM PDs. Atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) measurements demonstrate that the ODT organic molecules are chemically adsorbed on the surface of the AlGaN active layer successfully. The Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.6</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.4</sub> N MSM PD modified with ODT exhibits a cutoff wavelength of ~250 nm, and the dark current is reduced compared to the referential PD without ODT modification, indicating the decreased surface state density due to suppressible oxidation of AlGaN surface by using ODT modification. Moreover, the ODT-modified AlGaN PD shows a high peak responsivity of 2.75 A/W at 10 V, which is enhanced by ~3 times than that of the referential PD without modification.

(Invited) Complex Relative Permittivity of UV-C Transparent AlN

Development of high-power switching and radio frequency (RF) devices based on the ultrawide-bandgap (UWBG) AlGaN alloy system is generating interest in high Al composition alloys. The increase in bandgap as the alloy composition is varied from GaN to AlN is associated with an increase in the critical electric field, and thus the achievable breakdown voltage, of power devices based on these materials. In addition to the higher critical electric field, the relative insensitivity of saturation velocity to alloy composition offers prospects for RF applications. Also, high Al composition AlGaN transistors offer improved performance at high temperatures. Basic challenges, associated with controllable doping, electrical contacts, and passivation, remain for implementation of high Al composition alloys in these applications, but the expected improvement in device performance drives investigation of their properties. To date, both lateral and quasi-vertical power switching device geometries have been demonstrated (1), and the research on UWBG AlGaN transistors in power and RF electronics was recently reviewed (2).High-quality native substrates enable epitaxial growth of device heterostructures with low densities of threading dislocations, due to the low lattice and thermal mismatches to epitaxial active layers. Single crystal AlN substrates possess a high thermal conductivity and a close lattice match to high Al composition alloys, which make them an excellent choice for growth of AlGaN-based power switching and RF devices. Physical vapor transport growth (PVT) of 2-inch diameter AlN substrates free of low angle grain boundaries and with average threading dislocation densities below 103 cm-2 was recently demonstrated (3). However, high below-bandgap optical absorption in the ultraviolet-C (UV-C) region was observed in AlN grown by PVT in carbon-containing atmospheres, due to a deep-level absorption band related to the carbon impurity. This absorption band negatively impacts the efficiency of optoelectronic devices, which have driven adoption of AlN substrates to date, and typically require light extraction through the substrate. In this work, we studied the optical properties of double-side polished, 2-inch, c-plane AlN substrates by UV-Vis spectroscopy. Absorption coefficients were calculated by accurately accounting for reflection losses (4). Spatially uniform absorption coefficients below 30 cm-1 at 265 nm were demonstrated across 2-inch substrates. Furthermore, the calculated absorption and reflection coefficients were used to determine the complex refractive index and relative permittivity for the E⊥ c polarization in the 250-700 nm range, showing good agreement with published data for nominally unstrained, UV-C transparent bulk crystals.Finally, reliable values for the high-frequency and static permittivities, which are needed in the design of high-power electronic devices, were obtained.References R. J. Kaplar, A. A. Allerman, A. M. Armstrong, M. H. Crawford, J. R. Dickerson, A. J. Fischer, A. G. Baca, and E. A. Douglas, ECS J. Sol. State Sci. and Technol. 6(2), Q3061 (2017).A. G. Baca, A. M. Armstrong, B. A. Klein, A. A. Allerman, E. A. Douglas, and R. J. Kaplar, J. Vac. Sci. Technol. 38, 20803 (2020).R. Dalmau, J. Britt, H. Fang, B. Raghothamachar, M. Dudley, and R. Schlesser, Mater Sci. Forum 1004, 63 (2020).R. Dalmau, J. Britt, and R. Schlesser, ECS Trans. 98(6), 3 (2020).

Low Resistance Asymmetric III-Nitride Tunnel Junctions Designed by Machine Learning

The tunnel junction (TJ) is a crucial structure for numerous III-nitride devices. A fundamental challenge for TJ design is to minimize the TJ resistance at high current densities. In this work, we propose the asymmetric p-AlGaN/i-InGaN/n-AlGaN TJ structure for the first time. P-AlGaN/i-InGaN/n-AlGaN TJs were simulated with different Al or In compositions and different InGaN layer thicknesses using TCAD (Technology Computer-Aided Design) software. Trained by these data, we constructed a highly efficient model for TJ resistance prediction using machine learning. The model constructs a tool for real-time prediction of the TJ resistance, and the resistances for 22,254 different TJ structures were predicted. Based on our TJ predictions, the asymmetric TJ structure (p-Al0.7Ga0.3N/i-In0.2Ga0.8N/n-Al0.3Ga0.7N) with higher Al composition in p-layer has seven times lower TJ resistance compared to the prevailing symmetric p-Al0.3Ga0.7N/i-In0.2Ga0.8N/n-Al0.3Ga0.7N TJ. This study paves a new way in III-nitride TJ design for optical and electronic devices.

In situ passivation of Ga x In(1−x)P nanowires using radial Al y In(1−y)P shells grown by MOVPE

Ga x In(1−x)P nanowires with suitable bandgap (1.35–2.26 eV) ranging from the visible to near-infrared wavelength have great potential in optoelectronic applications. Due to the large surface-to-volume ratio of nanowires, the surface states become a pronounced factor affecting device performance. In this work, we performed a systematic study of Ga x In(1−x)P nanowires’ surface passivation, utilizing Al y In(1−y)P shells grown in situ by using a metal-organic vapor phase epitaxy system. Time-resolved photoinduced luminescence and time-resolved THz spectroscopy measurements were performed to study the nanowires’ carrier recombination processes. Compared to the bare Ga0.41In0.59P nanowires without shells, the hole and electron lifetime of the nanowires with the Al0.36In0.64P shells are found to be larger by 40 and 1.1 times, respectively, demonstrating effective surface passivation of trap states. When shells with higher Al composition were grown, both lifetimes of free holes and electrons decreased prominently. We attribute the acceleration of PL decay to an increase in the trap states’ density due to the formation of defects, including the polycrystalline and oxidized amorphous areas in these samples. Furthermore, in a separate set of samples, we varied the shell thickness. We observed that a certain shell thickness of approximately ∼20 nm is needed for efficient passivation of Ga0.31In0.69P nanowires. The photoconductivity of the sample with a shell thickness of 23 nm decays 10 times slower compared with that of the bare core nanowires. We concluded that both the hole and electron trapping and the overall charge recombination in Ga x In(1−x)P nanowires can be substantially passivated through growing an Al y In(1−y)P shell with appropriate Al composition and thickness. Therefore, we have developed an effective in situ surface passivation of Ga x In(1−x)P nanowires by use of Al y In(1−y)P shells, paving the way to high-performance Ga x In(1−x)P nanowires optoelectronic devices.

Plasma assisted molecular beam epitaxy growth mechanism of AlGaN epilayers and strain relaxation on AlN templates

Several series of high Al composition AlGaN epilayers were grown on AlN/sapphire templates by plasma assisted molecular beam epitaxy. Three growth regions, Ga droplets, intermediate Ga-rich, and N-rich, have been identified based on in situ and various ex situ characterizations, and AlGaN growth diagrams have been summarized. The Al composition is basically determined by Al supply when it is less than the effective N radical beam supply. X-ray diffraction reciprocal space maps have revealed residual strain status of AlGaN on AlN, demonstrating lattice relaxation as the layer thickness increases. The experimental critical thicknesses are observed increasing as Al composition increases, but they deviate from the theoretical values, which is attributed to the combined influence of nonequilibrium growth conditions, kinetics, phase separation and dislocation generation. Energy bandgaps were determined by optical absorption edges, suggesting a bowing parameter of 1.1 eV.

Investigation of quantum structure in N-polar deep-ultraviolet light-emitting diodes

This study systematically investigates the optical performance of N-polar deep-ultraviolet light-emitting diodes (DUV LEDs) in consideration of different quantum structures in the active region, with a highlight on various thicknesses of quantum barrier (QB), quantum well (QW), and the electron-blocking layer (EBL). The results show that the internal quantum efficiency (IQE), as well as light output power (LOP) of N-polar DUV LED, is not sensitive to QB thickness. On the contrary, the LOP and IQE performance can be significantly enhanced by increasing the QW thickness from 2 to 4 nm. Moreover, a saturated LOP in the N-polar DUV LEDs can be observed after QW thickness increased to a certain level as there is a trade-off between boosted carrier concentration and decreased wave function overlap in the active region. Lastly, the impact of the EBL on the optical performance of the N-polar DUV LED is also investigated. Specifically, a thicker EBL or a higher Al composition in the EBL leads to an increase in the turn-on voltage and series resistance while the LOP value remains unchanged. These findings lay the foundation for the development of high-performance N-polar DUV LEDs of the future.

MBE growth and donor doping of coherent ultrawide bandgap AlGaN alloy layers on single-crystal AlN substrates

Single-crystal Aluminum Nitride (AlN) crystals enable the epitaxial growth of ultrawide bandgap Al(Ga)N alloys with drastically lower extended defect densities. Here, we report the plasma-MBE growth conditions for high Al-composition AlGaN alloys on single-crystal AlN substrates. An AlGaN growth guideline map is developed, leading to pseudomorphic AlxGa1−xN epitaxial layers with x ∼0.6–1.0 Al contents at a growth rate of ∼0.3 μm/h. These epitaxial layers exhibit atomic steps, indicating step flow epitaxial growth, and room-temperature band edge emission from ∼4.5 to 5.9 eV. Growth conditions are identified in which the background impurity concentrations of O, C, Si, and H in the MBE layers are found to be very near or below detection limits. An interesting Si segregation and gettering behavior is observed at the epitaxial AlGaN/AlN heterojunction with significant implications for the formation and transport of 2D electron or hole gases. Well-controlled intentional Si doping ranging from ∼2 × 1017 to 3 × 1019 atoms/cm3 is obtained, with sharp dopant density transition profiles. In Si-doped Al0.6Ga0.4N epilayers, a room-temperature free electron concentration of ∼3 × 1019/cm3, an electron mobility of ∼27 cm2/V s, and an n-type resistivity of ∼7.5 m Ω cm are obtained. The implications of these findings on electronic and photonic devices on single-crystal AlN substrates are discussed.

Low-sheet-resistance high-electron-mobility transistor structures with strain-controlled high-Al-composition AlGaN barrier grown by MOVPE

We demonstrated low-sheet-resistance AlGaN high electron mobility transistors (HEMTs) using a strain-controlled high-Al-composition AlGaN barrier grown by MOVPE. We systematically investigated the effects of the AlGaN-barrier’s growth conditions on the electrical characteristics. We found that growing an AlGaN barrier with nitrogen as a carrier gas increases dislocation density in the AlGaN barrier, resulting in reduction of strain in the AlGaN barrier and the top of the GaN channel. Reduction strain in the GaN channel can improve electron mobility. Moreover, dislocation and impurity scattering are prevented using an AlN spacer. Finally, we achieved low-sheet-resistance HEMT structures with a high Al composition of over 0.60. The lowest sheet resistance is 211 Ω/sq. with electron mobility of 1820 cm2 V−1 s−1 using an Al0.68Ga0.32N barrier.

Effects of Al Composition and High-Temperature Atomic Layer-Deposited Al2O3 Layer on the Leakage Current Characteristics of AlGaN/GaN Schottky Barrier Diodes

AlGaN/GaN Schottky barrier diodes (SBDs) with high Al composition and high temperature atomic layer deposition (ALD) Al2O3 layers were investigated. Current–voltage (I–V), X-ray photoelectron spectroscopy (XPS), atomic force microscope (AFM), and capacitance–voltage (C–V) measurements were conducted in order to find the leakage current mechanism and reduce the reverse leakage current. The fabricated AlGaN/GaN SBDs with high Al composition exhibited two orders’ higher leakage current compared to the device with low Al composition (20%) due to large bulk and surface leakage components. The leakage current measured at −60 V for the fabricated SBD with Al2O3 deposited at temperature of 550 °C was decreased to 1.5 μA, compared to the corresponding value of 3.2 mA for SBD with nonpassivation layer. The high quality ALD Al2O3 deposited at high temperature with low interface trap density reduces the donorlike surface states, which effectively decreases surface leakage current of the AlGaN/GaN SBD.

The influence of Al composition in AlGaN barrier layer on polarization Coulomb field scattering in AlGaN/GaN heterostructure field-effect transistors

Abstract The AlGaN/GaN heterostructure field-effect transistors (HFETs) with the same size were fabricated on two AlGaN/GaN heterojunction materials with different Al composition. Based on the polarization Coulomb field (PCF) scattering theory model, the additional polarization charges and electron mobility are calculated. By analyzing the results, it is found that the increase of the Al composition in barrier layer will result in the increase of the additional polarization charges and the channel 2DEG density. Although HFETs with a higher Al composition in barrier layer have higher additional polarization charges, because of the higher density of 2DEG, the additional polarization charge has a weaker scattering effect on 2DEG, and the intensity of the PCF scattering is weaker. The contribution of additional polarization charges and 2DEG density to PCF scattering is opposite. The intensity of PCF scattering increases or decreases with the increase of Al composition, depending on which influence of the additional polarization charges and the 2DEG density is dominant..

Orthopyroxenite hosted chromitite veins anomalously enriched in platinum-group minerals from the Havana-Matanzas Ophiolite, Cuba

The Havana–Matanzas Ophiolite contains one of the few examples of ophiolitic platinum group minerals (PGM)-rich chromitites associated with orthopyroxenites in the mantle section of ophiolitic complexes. The chromitites occur as veins hosted by orthopyroxenite bands within mantle peridotites. The peridotites are mostly harzburgites and their accessory chromite shows high-Al compositions (Cr# [Cr/(Cr+Al), atomic ratio] = 0.39–0.50), which are typical of spinels in abyssal peridotites. Conversely, chromite from the chromitite veins and their host orthopyroxenite are high-Cr (Cr# = 0.72–0.73 and 0.62–0.69, respectively), with lower Mg# [Mg/(Mg+Fe2+), atomic ratio]. This suggests that both the chromitite and the orthopyroxenite formed from melts with boninitic affinity. The abundant PGM inclusions found in the chromitites are mainly Os-rich laurite grains, which is also characteristic of chromitites formed from magmas with boninitic affinity. Therefore, we propose that the chromitite veins and the orthopyroxenite bands probably formed contemporaneously in the fore-arc setting of an intra-oceanic arc during subduction. The chromitite-orthopyroxenite pair of the Havana-Matanzas Ophiolite could form after the reaction of a Si-rich melt with boninitic affinity and mantle harzburgite, with the orthopyroxenite bands preserving fingerprints of the infiltration of boninitic-affinity melts within the mantle. The small volume of forming chromitite could maximize the efficiency for the mechanical collection of the PGM forming in the parental melt of these rocks, resulting in the anomalous enrichment of primary PGM in the chromitites.

High Temperature Annealing SP-AlN Ameliorates the Crystal Quality ofAl&lt;sub&gt;0.5&lt;/sub&gt;Ga&lt;sub&gt;0.5&lt;/sub&gt;N Regrowth

In this study, the effect of a high-temperature annealing process on AlN is investigated. The high-temperature annealing process reduces the screw dislocation density of the AlN film to 2.1x107 cm-2. The AlN surface is highly flat. Through HRXRD and Raman spectroscopy, the stress mode changes in the sputtered AlN film before and after high-temperature annealing were studied in depth. Based on the HTA-AlN template, a high-quality, high-Al composition AlGaN epitaxial wafer, with a (0002) plane rocking curve FWHM of 246 arcsec , was prepared at 1080°C The growth mode of AlGaN grown directly on the AlN template at low temperature is summarized.

First-principles study on the structural stability and electronic properties of GaAs/Ga1−xAlxAs superlattice nanowires

In this study, the first-principles method is used to study the structural stability and electronic properties of GaAs/Ga1−xAlxAs and AlxGa1−xAs/AlyGa1−yAs superlattice nanowires. Calculations show that GaAs/Ga1−xAlxAs superlattice nanowires with smaller Al component spacing have higher structural stability. The increase of Al composition will further weaken the stability of GaAs/Ga1−xAlxAs heterostructure nanowires. Compared with the pure GaAs nanowires, the work function of GaAs/Ga1−xAlxAs heterostructure nanowires is all reduced, indicating that the variable Al composition heterostructure can enhance the photoemission ability. In addition, heterostructures with different configurations exhibit different electronic properties. Moreover, a powerful built-in electric field is formed across the GaAs/AlxGa1−xAs superlattice interface, which will further promote the migration of photoelectrons from low Al composition layer to high Al composition layer. GaAs/Ga1−xAlxAs superlattice nanowires are promising to be the high-performance photocathode materials.

MOCVD growth of β-phase (AlxGa1−x)2O3 on (2¯01) β-Ga2O3 substrates

β-(AlxGa1−x)2O3 thin films are grown on (2¯01) β-Ga2O3 substrates via metal organic chemical vapor deposition to investigate the solubility of Al in β-phase Ga2O3. The x-ray diffraction (XRD) spectra reveal crystalline quality (2¯01) β-(AlxGa1−x)2O3 thin films with Al compositions up to 48%. The Al compositions are further confirmed by high resolution x-ray spectroscopy measurements and energy-dispersive x-ray spectra (EDS) mapping. The bandgap energies extracted from XPS spectra range between 5.20 ± 0.06 eV and 5.72 ± 0.08 eV for x = 21%–48%. The surface morphology evaluated by both scanning electron microscopy and atomic force microscopy shows elongated features with granules along the [010] direction, which are suppressed with the increasing Al content. A systematic growth study through tuning growth parameters indicates that the chamber pressure plays an important role in both surface morphology and Al incorporation. Material characterization via high resolution scanning transmission electron microscopy and STEM-EDS reveals Al fluctuations in the sample with the 48% Al composition. Atomic resolution STEM imaging and XRD spectra for (2¯01) β-(AlxGa1−x)2O3/Ga2O3 superlattice structures confirm that the periodicity of the β-(AlxGa1−x)2O3/Ga2O3 sub-layers is well maintained with high-Al compositions.

Low-Frequency Noise Behavior of AlGaN/GaN HEMTs with Different Al Compositions

AlxGa1−xN/GaN heterostructures with two kinds of Al composition were grown by metal organic chemical vapor deposition (MOCVD) on sapphire substrates. The Al compositions in the AlGaN barrier layer were confirmed to be 13% and 28% using high resolution X-ray diffraction (HRXRD). AlxGa1−xN/GaN high-electron mobility transistors (HEMTs) with different Al compositions were fabricated, characterized, and compared using the Hall effect, direct current (DC), and low-frequency noise (LFN). The device with high Al composition (28%) showed improved sheet resistance (Rsh) due to enhanced carrier confinement and reduced gate leakage currents caused by increased Schottky barrier height (SBH). On the other hand, the reduced noise level and the low trap density (Nt) for the device of 13% of Al composition were obtained, which is attributed to the mitigated carrier density and decreased dislocation density in the AlxGa1−xN barrier layer according to the declined Al composition. In spite of the Al composition, the fabricated devices exhibited 1/ƒ noise behavior with the carrier number fluctuation (CNF) model, which is proved by the curves of both (SId/Id2) versus (gm/Id)2 and (SId/Id2) versus (Vgs–Vth). Although low Al composition is favorable to the reduced noise, it causes some problems like low Rsh and high gate leakage current. Therefore, the optimized Al composition in AlGaN/GaN HEMT is required to improve both noise and DC properties.

Spectroscopic analysis of allophane and imogolite samples with variable Fe abundance for characterizing the poorly crystalline components on Mars

AbstractNanophase materials including silicates, aluminosilicates, and iron oxides are widespread on Mars. These minerals are important because they likely represent a solid-phase record of ancient climatic conditions on the martian surface. Identification and characterization of nanophase compounds is technically challenging due to the small size and poorly ordered nature of these materials, particularly because their chemical compositions can vary widely.This study presents spectra of several synthetic allophane and imogolite samples with a range of chemical compositions that are typical of the natural variability of allophanic materials. These samples were formed under controlled conditions and have been thoroughly characterized in terms of chemical composition and short-range structure.Analyses confirmed that the synthetic materials were allophane and imogolite and were structurally similar to previously studied natural and synthetic examples of these phases. NMR and XAFS data indicated that high-Al proto-imogolite allophanes were similar in structure to imogolite but were less well ordered, and supported the proposed nanoball structures based on rolled octahedral Al sheets. Increasing Si content in allophane produced increasing tetrahedral Al substitution as well as polymerized Si chain structures at Al-Si mole ratios of 1:1, and sheets and possible framework structures at Al-Si mole ratios of 1:2. Fe in allophanes and imogolites substituted exclusively for octahedral Al.Reflectance spectra of the synthetic allophanes and imogolites were comparable to previously analyzed samples. Variations in Fe content of allophane and imogolite resulted in some observable changes in visible/near-infrared (VNIR) reflectance spectra, but these changes were not detectable in emission spectra. Emission spectra of the samples suggest that variations in Al-Si ratio of allophanes should be detectable using remotely sensed data. Because allophanes with different Al-Si ratios typically form in very different environments, this could be significant for interpretation of formation conditions on Mars, with high-Al compositions suggesting possible tephra weathering and high-Si compositions indicating possible formation from thermal waters.

The influence of point defects on AlGaN-based deep ultraviolet LEDs

AlGaN-based deep ultraviolet LEDs with high Al composition are promising for many applications, including air- or water-purification, fluorescence sensing, etc. However, to realize their full potential, it is important to understand the impact of the point defects on the device performance. Here, we investigate the defects in the 265 nm AlGaN-based deep ultraviolet LEDs after degradation systematically with a combination of different analytical technologies. The results show that point defects increase after the degradation. The generated defects during the stress lead to a carrier redistribution in the active region and the induced point defects during the degradation are located within the multi-quantum wells (MQWs) region, especially in the first quantum well near the p side of the LED chip. The dislocation lines in the MQWs region were also observed after the degradation, which can lead to the Mg diffusion along the dislocation line. These findings are important to understand the defects in AlGaN quantum wells and further improve AlGaN-based deep ultraviolet LEDs’ performance.