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AlGaN deep-ultraviolet light-emitting diodes grown on SiC substrates
摘要： The disinfection industry would greatly benefit from efficient, robust, high-power deep-ultraviolet light-emitting diodes (UV-C LEDs). However, the performance of UV-C AlGaN LEDs is limited by poor light-extraction efficiency (LEE) and the presence of a large density of threading dislocations. We demonstrate high power AlGaN LEDs grown on SiC with high LEE and low threading dislocation density. We employ a crack-free AlN buffer layer with low threading dislocation density and a technique to fabricate thin-film UV LEDs by removing the SiC substrate, with a highly selective SF6 etch. The LEDs (278 nm) have a turn-on voltage of 4.3 V and a CW power of 8 mW (82 mW/mm2) and external quantum efficiency (EQE) of 1.8% at 95 mA. KOH submicron roughening of AlN surface (nitrogen-polar) and improved p-contact reflectivity are found to be effective in improving the LEE of UV light. We estimate the improved LEE by semi-empirical calculations to be 33% (without encapsulation). This work establishes UV LEDs grown on SiC substrates as a viable architecture to large-area, high-brightness, and high power UV LEDs.
关键词： AlGaN LEDs,UV-C LEDs,light extraction efficiency,disinfection technology,AlN,external quantum efficiency,SiC,substrate removal
更新于2025-09-19 17:13:59
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Eutectic Formation, V/III Ratio, and Controlled Polarity Inversion in Nitrides on Silicon
摘要： The crystallographic polarity of AlN grown on Si(111) by plasma-assisted molecular beam epitaxy is intentionally inverted from N-polar to Al-polar at a planar boundary. The position of the inversion boundary is controlled by a two-step growth process that abruptly changes from Al-rich to N-rich growth conditions. The polarity inversion is induced by the presence of Si, which is incorporated from an Al–Si eutectic layer that forms during the initial stages of AlN growth and floats on the AlN surface under Al-rich growth conditions. When the growth conditions change to N-rich, the Al and Si in the eutectic react with the additional N-flux and are incorporated into the solid AlN film. Relatively low levels of Al–Si eutectic formation combined with lateral variations in the Si incorporation lead to nonuniformity in the polarity inversion and formation of surprisingly narrow, vertical inversion domains. The results suggest that intentional incorporation of uniform layers of Si may provide a method for producing polarity engineered nitride structures.
关键词： AlN,Si incorporation,scanning transmission electron microscopy,polarity inversion,nitride structures,eutectic layer
更新于2025-09-16 10:30:52
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Study of optical and structural properties of sputtered aluminum nitride films with controlled oxygen content to fabricate Distributed Bragg Reflectors for ultraviolet A
摘要： Aluminum nitride (AlN) films with controlled oxygen content were deposited on silicon substrates, and optical properties studied with dependency on film morphology. Combinations of argon (Ar) and nitrogen (N2) gases were used in RF magnetron sputtering of an AlN target. The resulting refractive index ranging from 1.6 to 2.0 at 400 nm was tuned by controlling the sputter gas flow rate ratio of Ar and N2. The resulting refractive index is associated with density and aluminum nitride content of the thin films. Distributed Bragg Reflectors (DBRs) optimized for ultraviolet-A reflectivity were fabricated with pairs of alternating AlN thin films using an explicit combination of low-n and high-n to further investigate the thin film optical properties. The effect of structural transformation in the DBR stack on the progress of optical properties was studied. The DBRs exhibit a negligible extinction coefficient, utilizing precise control of oxygen incorporation with one sputtering target.
关键词： Optical properties,Materials interface,Aluminum oxynitride,Aluminum nitride,AlN,Refractive index,DBR,Magnetron sputtering
更新于2025-09-16 10:30:52
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[IEEE 2019 International Conference on Numerical Simulation of Optoelectronic Devices (NUSOD) - Ottawa, ON, Canada (2019.7.8-2019.7.12)] 2019 International Conference on Numerical Simulation of Optoelectronic Devices (NUSOD) - The Influence of Periodic Ultra-thin AlN Interlayers in Multiplication Region on the GaN Avalanche Photodiode
摘要： GaN APD with periodic ultra-thin AlN interlayers in multiplication region has been proposed to obtain a high gain at constant voltage mode. The influence of interlayers on the multiplication process was the AlN numerically simulated and analyzed. The results predict that the multiplication process contains three different stages with the increase of the reverse voltage. The experimental results agree with the numerically simulation very well and a high gain of 6×104 at constant voltage mode was obtained.
关键词： constant voltage mode,Avalanche photodiodes,AlN interlayers,high gain
更新于2025-09-16 10:30:52
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The Effect of Inductively Coupled Plasma Etching on the I–V Curves of the APD with GaN/AlN Periodically‐Stacked‐STRUCTURE
摘要： Inductively Coupled Plasma (ICP) is widely used in dry etching of III-nitride materials, wherein the etching parameters of GaN and AlN are very different. In this paper, the ICP dry etching process parameters of GaN/AlN periodically-stacked-structure (PSS) for avalanche photodiode fabrication have been intensively studied and optimized. The flow rate ratio of Cl2/BCl3/Ar plasma, bias voltage, and the GaN-to-SiNx selectivity of ICP etching were optimized to achieve excellent surface morphology and nearly vertical sidewalls. It was found that the etching rate and the etched surface roughness of GaN/AlN material were significantly influenced by the flow rate of Cl2. After optimizing the etching procedure, the root-mean-square roughness (RMS) of the etched surface was measured to be 1.46 nm, which is close to the as grown surface. By employing the optimized ICP dry etching in the fabrication of the GaN/AlN PSS avalanche photodiode (APD), the dark current was suppressed from 3.6 A/cm2 to 8.2×10-3 A/cm2 at -90 V.
关键词： GaN/AlN,dark current,molecular beam epitaxy,inductively coupled plasma,avalanche photodiode
更新于2025-09-12 10:27:22
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Deep UV laser at 249 nm based on GaN quantum wells
摘要： In this letter, we report on deep UV laser emitting at 249 nm based on thin GaN quantum wells (QWs) by optical pumping at room temperature. The laser threshold was 190 kW/cm2 that is comparable to state-of-the-art AlGaN QW lasers at similar wavelengths. The laser structure was pseudomorphically grown on a c-plane sapphire substrate by metalorganic chemical vapor deposition, comprising 40 pairs of 4 monolayer (ML) GaN QWs sandwiched by 6 ML AlN quantum barriers (QBs). The low threshold at the wavelength was attributed to large optical and quantum confinement, and high quality of the material, interface, and Fabry-P?rot facet. The emissions below and above the threshold were both dominated by transverse electric polarizations thanks to the valence band characteristics of GaN. This work unambiguously demonstrates the potentials of the binary AlN/GaN heterojunctions for high-performance UV emitters.
关键词： GaN quantum wells,deep UV laser,UV emitters,AlN/GaN heterojunctions,optical pumping
更新于2025-09-12 10:27:22
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Determination of Sapphire Off‐Cut and its Influence on the Morphology and Local Defect Distribution in Epitaxially Laterally Overgrown AlN for Optically Pumped UVC Lasers
摘要： In this paper a systematic study of the morphology and local defect distribution in epitaxial laterally overgrown (ELO) AlN on c-plane sapphire substrates with different off-cut angles is presented. Precise measurements of the off-cut angle, using a combination of optical alignment and X-ray diffraction with an accuracy of ±5° for the off-cut direction and ±0.015° for the off-cut angle were performed. For ELO AlN growth a transition from step flow growth at a < 0.14° with height undulations on the surface to step bunching with step heights up to 20 nm for a > 0.14° was observed. Furthermore, the terraces of the step bunched surface exhibit curved steps. An analysis of the local defect distribution by scanning transmission electron microscopy and a comparison with atomic force microscopy reveals a bunching of defects in line with the ELO pattern and a roughening of step edges in highly defective regions. In addition, a reduction of the threshold excitation power density for optically pumped UVC lasers with smooth surface morphologies was observed.
关键词： AlN,off-cut,optically pumped laser,sapphire,UVC,ELO
更新于2025-09-11 14:15:04
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Improved interfacial properties of thermal atomic layer deposited AlN on GaN
摘要： The interfacial properties of atomic layer deposited AlN on n-GaN substrate were investigated. Capacitance–voltage (CeV) characteristics showed that the sample with a 24 nm thick AlN had lower interface state density than the sample with a 7.4 nm thick AlN. Analysis on the X-ray photoelectron spectroscopy (XPS) spectra showed the better AlN formation near the AlN/GaN interface with a 24 nm thick AlN. The dominant peak shift to lower binding energy in the Al 2p core level spectra was observed with increasing the AlN thickness, which could be due to the strain relaxation resulted from the lattice mismatch between AlN and GaN.
关键词： Atomic layer deposited AlN,Interface state density,AlN/GaN
更新于2025-09-10 09:29:36
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Repeatable Room Temperature Negative Differential Resistance in AlN/GaN Resonant Tunneling Diodes Grown on Sapphire
摘要： Resonant tunneling diodes (RTDs) are candidates for high power terahertz oscillators, and form the basis for understanding the quantum confinement and vertical transport in quantum structures such as quantum cascade lasers and quantum cascade detectors. In this work, repeatable negative differential resistance (NDR) is achieved in AlN/GaN RTDs grown on sapphire substrate by plasma-assisted molecular-beam epitaxy. Two reproducible NDR regions sequentially following two preresonance replicas are demonstrated at room temperature. A current region exhibiting negative correlation with temperature and oscillation-like features is first identified under reverse bias, which is interpreted as a combined contribution of weak resonant tunneling channels through different bound states in the well. The revealed peak-to-valley current ratio ranges from 1.1 to 1.8, and peak current density ranges from 5 to 164 kA cm?2. Using an analytic model, resonant tunneling transports in both bias directions are quantitatively characterized and show good agreements with experiment results, demonstrating the capability of accurate quantum transport control using III-nitride grown on sapphire substrate. The findings will promote the implementation of low cost III-nitride monolithic microwave circuits and resonant tunneling structures based on sapphire, SiC, and even silicon substrates.
关键词： sapphire substrate,AlN/GaN resonant tunneling diodes,repeatable negative differential resistance
更新于2025-09-10 09:29:36
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[IEEE 2018 19th International Conference on Electronic Packaging Technology (ICEPT) - Shanghai (2018.8.8-2018.8.11)] 2018 19th International Conference on Electronic Packaging Technology (ICEPT) - Study on Interfacial Diffusion Mechanism of The Nonstoichiometric ratio TiN0.3 and AlN composite in the process of sintering
摘要： Covalent compounds have strong covalent bond, thus showing high melting point, high hardness, high temperature resistance, corrosion resistance, wear resistance and other excellent performance, is widely applied to the field of refractory materials and wear-resistant materials.But at the same time this kind of material also has the problem of poor toughness and difficulty in sintering.In this article, by adding the nonstoichiometric ratio to the AlN titanium nitride, a new method were studied to improve the sintering property and reduce the sintering temperature through vacancy diffusion and to study the sintering of micro forming mechanism. The experimental results show that after sintering at the interface between TiN0.3 and AlN two-phase, the TiN0.3 / AlN layer have apparent diffusion zone, AlN in N, Al atom diffusion in TiN0.3 via the vacancy diffusion mechanism. As a result of the existence of a large amount of N of TiN0.3 space, when the diffusion of N atomic migration is absorbed by vacancy,and approaches stoichiometric ratio TiN layer AlN substrate;Al atoms crystallized out of the TiN layer in the hexagonal AlN structure in TiN0.3 matrix.
关键词： Covalent compounds,AlN,Interface densification,non-stoichiometric TiNx
更新于2025-09-10 09:29:36