Development of an accurate hand-held sensing platform for nitrite detection based on nitrogen-doped carbon dots.

As is well known, excessive nitrite can seriously pollute the environment and can harm human health. Although existing methods can be used to determine nitrite content, they still have some drawbacks, such as relatively complicated operation and expensive equipment. Herein, a hand-held sensing platform (HSP) for NO2- determination was developed. First, ammonia-rich nitrogen-doped carbon dots with orange-yellow emission were designed and synthesised, which were suitable as fluorescent probes because of their good optical properties and stability. Then, the HSP based on fluorescence using photoelectric conversion technology was designed and manufactured using three-dimensional printing technology. Under optimum conditions, the voltage (V/V0) of the proposed HSP showed good linearity for NO2- detection in the range of 10-500 µM, with a detection limit of 1.95 µM. This portable sensor showed good stability, accuracy and reliability in detecting actual water and meat samples, which may ensure food safety in practical applications. Moreover, the HSP is compact, portable and easily assembled and is suitable for on-site real-time detection, which shows great application potential and prospects.

Monitoring Poly(methyl methacrylate) and Polyvinyl Dichloride Micro/Nanoplastics in Water by Direct Solid-Phase Microextraction Coupled to Gas Chromatography-Mass Spectrometry.

A simple, sustainable, and sensitive monitoring approach of micro/nanoplastics (MNPs) in aqueous samples is crucial since it helps in assessing the extent of contamination and understanding the potential risks associated with their presence without causing additional stress to the environment. In this study, a novel strategy for qualitative and quantitative determination of MNPs in water by direct solid-phase microextraction (SPME) coupled with gas chromatography-mass spectrometry (GC-MS) was proposed for the first time. Spherical poly(methyl methacrylate) (PMMA) and irregularly shaped polyvinyl dichloride (PVDC) were used to evaluate the feasibility and performance of the proposed method. The results demonstrated that both PMMA and PVDC MNPs were efficiently extracted by the homemade SPME coating of nitrogen-doped porous carbons (N-SPCs) and exhibited sufficient thermal decomposition in the GC-MS injection port. Excellent extraction performances of N-SPCs coating for MNPs are attributed to hydrophobic cross-linking, electrostatic forcing, hydrogen bonding, and pore trapping. Methyl methacrylate was identified as the marker for PMMA, while 1,3-dichlorobenzene and 1,3,5-trichlorobenzene were the indicators for PVDC. Under the optimal extraction and decomposition conditions, the proposed method exhibited ultrahigh sensitivity, with a limit of detection of 0.0041 µg/L for PMMA and 0.0054 µg/L for PVDC. Notably, a programmed temperature strategy for the GC-MS injector was developed to discriminate and eliminate the potential interferences of intrinsic indicator compounds. Owing to the integration of sampling, extraction, injection, and decomposition into one step by SPME, the proposed method demonstrates exceptional sensitivity, eliminating the necessity for complex sample pretreatment procedures and the use of organic solvents. Finally, the proposed method was successfully applied in the determination of PMMA and PVDC MNPs in real aqueous samples.

Quantitative Determination of Poly(methyl Methacrylate) Micro/Nanoplastics by Cooling-Assisted Solid-Phase Microextraction Coupled to Gas Chromatography-Mass Spectrometry: Theoretical and Experimental Insights.

Determinations of micro/nanoplastics (MNPs) in environmental samples are essential to assess the extent of their presence in the environment and their potential impact on ecosystems and human health. With the aim to provide a sensitive method with simplified pretreatment steps, cooling-assisted solid-phase microextraction (CA-SPME) coupled to gas chromatography-mass spectrometry (GC-MS) is proposed as a new approach to quantify mass concentrations of MNPs in water and soil samples. The herein proposed CA-SPME method offers the unique advantage of integrating the thermal decomposition of MNPs and enrichment of signature compounds into one step. Poly(methyl methacrylate) (PMMA) was used as a model substance to verify the method performance in this work. Theoretical insights demonstrated that pyrolysis is the rate-determining step during the extraction process and that PMMA is effectively decomposed at 350 °C with an estimated incubation time of 13 min. Eight compounds were identified in the pyrolysis products by CA-SPME-GC-MS with the use of a DVB/CAR/PDMS coating, wherein methyl methacrylate was considered as the best indicator and dimethyl 2-methylenesuccinate was selected as the confirmation compound. Under the optimized conditions, the proposed method exhibited wide linearity (0.5-2000 µg for water and 5-1000 µg for soil) and high sensitivity, with limits of detection of 0.014 and 0.28 µg for water and soil, respectively. Finally, the proposed method was successfully applied for determinations of PMMA MNPs in real water and soil samples with satisfactory recoveries attained. The method only required the employment of a filter membrane for water analysis, while soil samples were analyzed directly without any pretreatment. The solvent-free approach, straightforward operation, and high sensitivity of the proposed method show great potential for the analysis of MNPs in different environmental samples.

Improved crystal quality and enhanced optical performance of GaN enabled by ion implantation induced high-quality nucleation.

Hetero-epitaxial growth of GaN often leads to high density of threading dislocations, which poses a significant challenge to the promotion of the performance of GaN-based devices. In this study, we address this issue by utilizing an Al-ion implantation pretreatment on sapphire substrates, which induces high-quality regularly arranged nucleation and promotes the crystal quality of GaN. Specifically, we demonstrate that an Al-ion dose of 1013 cm-2 leads to a reduction of full width at half maximum values of (002)/(102) plane X-ray rocking curves from 204.7/340.9 arcsec to 187.0/259.5 arcsec. Furthermore, a systematic investigation of GaN film grown on the sapphire substrate with various Al-ion doses is also performed, and the nucleation layer growth evolution on different sapphire substrates is analyzed. As confirmed by the atomic force microscope results of the nucleation layer, the ion implantation induced high-quality nucleation is demonstrated, which results in the improved crystal quality of the as-grown GaN films. Transmission electron microscope measurement also proves the dislocation suppression through this method. In addition, the GaN-based light-emitting diodes (LEDs) were also fabricated based on the as-grown GaN template and the electrical properties are analyzed. The wall-plug efficiency at 20 mA has risen from 30.7% to 37.4% of LEDs with Al-ion implantation sapphire substrate at a dose of 1013 cm-2. This innovative technique is effective in the promotion of GaN quality, which can be a promising high-quality template for LEDs and electronic devices.

Cellulose Nanocrystals Induced Loose and Porous Graphite Phase Carbon Nitride/Porous Carbon Composites for Capturing and Determining of Organochlorine Pesticides from Water and Fruit Juice by Solid-Phase Microextraction.

Herein, novel, loose, and porous graphite phase carbon nitride/porous carbon (g-C3N4@PC) composites were prepared by decorating cellulose nanocrystals (CNCs). The characterization results demonstrate that the as-prepared composites presented high specific surface areas, porous structures, and abundant chemical groups, with the modification of CNCs. In view of the unique advantages, g-C3N4@PC was used as the coating material for the solid-phase microextraction (SPME) of organochlorine pesticides (OCPs) in water and juice samples. The g-C3N4@PC-coated fibers showed better extraction efficiencies than commercial fibers (100/7 µm PDMS and PA) toward the OCPs, with the enrichment factors of the g-C3N4@PC-coated fibers 5-30 times higher than the latter. Using a gas chromatography-mass spectrometry (GC-MS) instrument, the g-C3N4@PC-coated fibers exhibited a gratifying analytical performance for determining low concentrations of OCPs, with a wide linear range (0.1-1600 ng L-1 for water; 0.1-1000 ng L-1 for juice), low limits of detection (0.0141-0.0942 ng L-1 for water; 0.0245-0.0777 ng L-1 for juice), and good reproducibility and repeatability in optimal conditions. The established method showed good sensitivity and recovery in the determination of OCPs in the water and fruit juice samples, which displayed broad prospects for analyzing organic pollutants from environmental samples.

Polyacrylic Acid Functionalized Biomass-Derived Carbon Skeleton with Highly Porous Hierarchical Structures for Efficient Solid-Phase Microextraction of Volatile Halogenated Hydrocarbons.

In this study, polyacrylic acid functionalized N-doped porous carbon derived from shaddock peels (PAA/N-SPCs) was fabricated and used as a solid-phase microextraction (SPME) coating for capturing and determining volatile halogenated hydrocarbons (VHCs) from water. Characterizations results demonstrated that the PAA/N-SPCs presented a highly meso/macro-porous hierarchical structure consisting of a carbon skeleton. The introduction of PAA promoted the formation of polar chemical groups on the carbon skeleton. Consequently, large specific surface area, highly hierarchical structures, and abundant chemical groups endowed the PAA/N-SPCs, which exhibited superior SPME capacities for VHCs in comparison to pristine N-SPCs and commercial SPME coatings. Under the optimum extraction conditions, the proposed analytical method presented wide linearity in the concentration range of 0.5-50 ng mL-1, excellent reproducibility with relative standard deviations of 5.8%-7.2%, and low limits of detection varying from 0.0005 to 0.0086 ng mL-1. Finally, the proposed method was applied to analyze VHCs from real water samples and observed satisfactory recoveries ranging from 75% to 116%. This study proposed a novel functionalized porous carbon skeleton as SPME coating for analyzing pollutants from environmental samples.

High-throughput profiling volatiles in edible oils by cooling assisted solid-phase microextraction technique for sensitive discrimination of edible oils adulteration.

In this study, a cooling assisted solid-phase microextraction technique (CA-SPME) was proposed and used for identifying volatile and semi-volatile compounds in edible oil innovatively coupled to gas chromatography-mass spectrometry. Compared with regular SPME technique, CA-SPME presented significantly higher extraction efficiencies for analytes in edible oil due to its synergistic effect of heating and cooling. After optimization of the extraction conditions including heating temperature, cooling temperature, extraction time, and added amount of edible oil, thirty-eight, thirty-six, twenty-nine, and thirty-three kinds of compounds in peanut oil, olive oil, canola oil, and soybean oil were successfully identified, respectively, using DVB/CAR/PDMS coating with extraction time of 30 min and edible oil amounts of 20 µL. Principal component analysis, partial least squares discriminant analysis, and hierarchical clustering analysis (HCA) were performed to evaluate the potential of proposed method in discriminating edible oils adulteration (peanut oil adulterated with canola oil, peanut oil adulterated with soybean oil, olive oil adulterated with canola oil) subsequently. Results demonstrated that the method was useful in successful discrimination of pure and adulterated edible oils with adulteration percentages ranging from 0.5 to 10%. Furthermore, volatiles contributing to classifications between pure and adulterated edible oils were also illustrated based on variable importance for the projection analysis and distributions of volatiles in HCA heatmaps. The proposed method provided a novel strategy for sensitive detection of edible oil adulteration without any other sample pretreatment.

Lotus-like Ni@NiO nanoparticles embedded porous carbon derived from MOF-74/cellulose nanocrystal hybrids as solid phase microextraction coating for ultrasensitive determination of chlorobenzenes from water.

Lotus-like Ni@NiO embedded porous carbons (Ni@NiO/PCs) were fabricated by pyrolysis of MOF-74/cellulose nanocrystal hybrids, and used as a solid phase microextraction (SPME) coating for ultrasensitive determination of chlorobenzenes (CBs) from water combined with gas chromatography-mass spectrometry. Owing to its abundant chemical groups, high porosity, and excellent thermal stability, the as-prepared Ni@NiO/PCs presented superior extraction performance compared to commercial SPME coatings. Notably, Ni@NiO/PCs derived from MOF-74/CNC hybrids presented higher extraction efficiencies towards CBs than that derived from pristine CNC and MOF-74 due to the formation of micro/mesopores and more abundant oxygen-containing groups. Under the optimum extraction conditions, the proposed analytical method presented wide linearity range (0.5-1500 ng L-1), ultra-low detection of limit (0.005-0.049 ng L-1), and excellent precision with relative standard deviations of 4.7-9.2% for a single fiber and 8.8-10.9% for 5 fibers, and long lifetime (≥160 times). The proposed analytical method was finally applied for determination of CBs from real water samples, and the recoveries were in the range of 93.2-116.8% towards eight CBs. This study delivered a novel and efficient sorbent as SPME coating to extraction and determination of CBs from water.

Carbon Dot-Decorated Graphite Carbon Nitride Composites for Enhanced Solid-Phase Microextraction of Chlorobenzenes from Water.

In this work, carbon dot-decorated graphite carbon nitride composites (CDs/g-C3N4) were synthesized and innovatively used as a SPME coating for the sensitive determination of chlorobenzenes (CBs) from water samples, coupled with gas chromatography-mass spectrometry. The CDs/g-C3N4 coating presented superior extraction performance in comparison to pristine g-C3N4, owing to the enhancement of active groups by CDs. The extraction capacities of as-prepared SPME coatings are higher than those of commercial coatings due to the functions of nitrogen-containing and oxygen-containing group binding, π-π stacking, and hydrophobic interactions. Under optimized conditions, the proposed method exhibits a wide linearity range (0.25-2500 ng L-1), extremely low detection of limits (0.002-0.086 ng L-1), and excellent precision, with relative standard deviations of 5.3-9.7% for a single fiber and 7.5-12.6% for five fibers. Finally, the proposed method was successfully applied for the analysis of CBs from real river water samples, with spiked recoveries ranging from 73.4 to 109.1%. This study developed a novel and efficient SPME coating material for extracting organic pollutants from environmental samples.

Core-shell structured Fe2O3/CeO2@MnO2 microspheres with abundant surface oxygen for sensitive solid-phase microextraction of polycyclic aromatic hydrocarbons from water.

Core-shell structured Fe2O3/CeO2@MnO2 microspheres were fabricated and used as solid-phase microextraction coating for determination of polycyclic aromatic hydrocarbons (PAHs) in water samples. XPS spectra demonstrated the generation of abundant surface oxygen on Fe2O3/CeO2@MnO2 microspheres, which provided binding sites for enhancement of analyte extraction. Under optimized conditions, the proposed method presented good linearity in the concentration range 0.04-100 ng mL-1, with low limits of detection varying from 0.38 to 3.57 ng L-1 for eight PAHs. Relative standard deviations for a single fiber and five batches of fibers were in the ranges of 4.1-8.2% and 7.1-11.4%, respectively. The proposed method was successfully used for determination of PAHs in real river water samples with recoveries ranging from 87.1 to 115.9%. The proposed method using as-prepared Fe2O3/CeO2@MnO2 microspheres as SPME coating exhibit significant potential for real sample analysis due to its excellent reproducibility, high sensitivity, and good linearity.

Facile fabrication of magnetic covalent organic frameworks for magnetic solid-phase extraction of diclofenac sodium in milk.

A robust magnetic solid-phase extraction (MSPE) method based on magnetic covalent organic framework (MCOF) coupled with high-performance liquid chromatography (HPLC)-ultraviolet (UV)/mass spectrometry (MS) was proposed for the determination of trace diclofenac sodium (DS) in milk. The prepared MCOF exhibited high extraction efficiency, which can be attributed to its high specific surface area as well as strong π-π and hydrophobic interactions between MCOF and DS. In addition, the potential influencing factors, including sample volume, adsorbent dosage, extraction time, and elution parameters, were fully estimated. The experimental results demonstrated that the established method was sensitive for the quantification of DS with high accuracy. Remarkably, the detection limit of DS was found to be 10 ng/kg under the optimal conditions. More impressively, the developed method was successfully applied to monitor trace DS in milk, demonstrating its outstanding durability and practical potential as an appealing method to regular monitor trace pharmaceutical contaminants in real food samples.

Epitaxial Growth of GaN on Magnetron Sputtered AlN/Hexagonal BN/Sapphire Substrates.

Magnetron sputtering is adopted to deposit ~25 nm thick AlN on the surface of hexagonal BN(h-BN)/sapphire substrates, followed by epitaxial GaN growth on top of the AlN/h-BN/sapphire substrate using a metal-organic chemical vapor deposition system. Compared to GaN grown on the h-BN/sapphire surface directly, this method results in a continuous and smooth GaN film with a smaller root mean square roughness. Besides, the introduction of the sputtered AlN layer reduces the dislocation density of GaN by 35.7%. We provide a pathway of GaN epitaxy on the h-BN surface, which significantly improves its surface morphology and crystal quality.

Comparative Research of GaN Growth Mechanisms on Patterned Sapphire Substrates with Sputtered AlON Nucleation Layers.

The utilization of sputtered AlN nucleation layers (NLs) and patterned sapphire substrates (PSSs) could greatly improve GaN crystal quality. However, the growth mechanism of GaN on PSSs with sputtered AlN NLs has not been thoroughly understood. In this paper, we deposited AlON by sputtering AlN with O2, and we found that the variation of thickness of sputtered AlON NLs greatly influenced GaN growth on PSSs. (1) For 10 nm thin AlON sputtering, no AlON was detected on the cone sidewalls. Still, GaN nucleated preferably in non-(0001) orientation on these sidewalls. (2) If the thickness of the sputtered AlON NL was 25 nm, AlON formed on the cone sidewalls and flat regions, and some small GaN crystals formed near the bottom of the cones. (3) If the sputtered AlON was 40 nm, the migration ability of Ga atoms would be enhanced, and GaN nucleated at the top of the cones, which have more chances to grow and generate more dislocations. Finally, the GaN growth mechanisms on PSSs with sputtered AlON NLs of different thicknesses were proposed.

Determination of Ferulic Acid in Angelica sinensis by Temperature-Controlled Hydrophobic Ionic Liquids-Based Ultrasound/Heating-Assisted Extraction Coupled with High Performance Liquid Chromatography.

Hydrophilic ionic liquids are often used to extract the active ingredients of medicinal plants, while hydrophobic ionic liquids are rarely used to directly extract solid samples. In this paper, a simple, novel and efficient temperature-controlled hydrophobic ionic liquids-based ultrasound/heating-assisted extraction (TC-ILs-UHAE) procedure coupled with high-performance liquid chromatography (HPLC) was developed and applied to the determination of ferulic acid (FA) in Chinese herbal medicine Angelica sinensis. During the extraction procedure, hydrophobic ionic liquids (ILs) were dispersed into water to form cloudy solution (fine droplets) with the aid of ultrasound and heating simultaneous. After extraction, phase separation was easily achieved by centrifuging at 0 °C. Among all ILs used, 1-butyl-3-methylimidazolium bis(trifluoromethanesulphonyl)imide ([C4mim]NTf2) exhibited the highest extraction ability and the possible extraction mechanism was discussed. Additionally, the synergistic effect of heating and ultrasound on the extraction efficiency was investigated. Under the optimized conditions, a good linearity was observed with correlation coefficient (r) of 0.9995. The limit of detection of FA (LOD, S/N = 3) was 9.6 µg/L and the spiked recoveries of FA for real samples were in the range of 91.67 to 102.00% with relative standard deviation (RSD) lower than 3.87%. Compared with the traditional extraction methods, the proposed method gave the highest yield of FA and had the shortest extraction time. Therefore, this method is a potential simple, green and highly efficient technique and expected to be applied to the extraction of other bioactive ingredients in medicinal plants.

A facile cooling-assisted solid-phase microextraction device for solvent-free sampling of polycyclic aromatic hydrocarbons from soil based on matrix solid-phase dispersion technique.

Solvent-free analysis of organic pollutants from a complex matrix has attracted significant attention. In this work, we designed and fabricated a facile cooling-assisted solid-phase microextraction device (CA-SPME) that could be used for the solvent-free extraction of volatile and semivolatile compounds from a complex matrix using a commercial SPME probe. Determination of polycyclic aromatic hydrocarbons (PAHs) from soil samples was carried out to evaluate the performance of the designed CA-SPME device. The effects of heating temperature, cooling temperature, extraction time, and moisture content in soil on extraction efficiency were investigated. To enhance the extraction efficiency of the targeted analytes, the matrix solid-phase dispersion technique (MSPD) by grinding soil with silica gels was applied. The results showed that grinding with silica gels promoted the release of PAHs from the soil matrix to the headspace by disrupting the matrix structure, which then facilitated the extraction efficiency. Under optimized conditions, for all of the targeted PAHs, the method exhibited good linearity (40-4000 ng g-1) with regression coefficients (R2) ranging from 0.9586 to 0.9964. The limits of detection and limits of quantification ranged from 4.2 to 8.5 ng g-1 and 14.0-28.5 ng g-1, respectively. Relative standard deviations corresponding to the analysis of spiked soil samples (n = 5) were 8.1-13.4%. The solvent-free analysis of the certified soil sample using the proposed method demonstrated satisfactory results.

High-Performance AlGaN Double Channel HEMTs with Improved Drain Current Density and High Breakdown Voltage.

In this work, AlGaN double channel heterostructure is proposed and grown by metal organic chemical vapor deposition (MOCVD), and high-performance AlGaN double channel high electron mobility transistors (HEMTs) are fabricated and investigated. The implementation of double channel feature effectively improves the transport properties of AlGaN channel heterostructures. On one hand, the total two dimensional electron gas (2DEG) density is promoted due to the double potential wells along the vertical direction and the enhanced carrier confinement. On the other hand, the average 2DEG density in each channel is reduced, and the mobility is elevated resulted from the suppression of carrier-carrier scattering effect. As a result, the maximum drain current density (Imax) of AlGaN double channel HEMTs reaches 473 mA/mm with gate voltage of 0 V. Moreover, the superior breakdown performance of the AlGaN double channel HEMTs is also demonstrated. These results not only show the great application potential of AlGaN double channel HEMTs in microwave power electronics but also develop a new thinking for the studies of group III nitride-based electronic devices.

Using a Multi-Layer Stacked AlGaN/GaN Structure to Improve the Current Spreading Performance of Ultraviolet Light-Emitting Diodes.

To obtain excellent current spreading performance of ultraviolet light-emitting diodes (UVLEDs), a 60-period stacked Si modulation-doped n-AlGaN/u-GaN structure is proposed to replace the traditional n-AlGaN structure. The high-resolution X-ray diffraction ω-scan rocking curves show that the periodic growth of AlGaN and GaN layers plays a positive role in reducing dislocation density. Compared with the conventional UV light-emitting diodes (LEDs), light emission micrographs of devices with a multi-layer stacked n-AlGaN/u-GaN structure reveal higher brightness and a more uniform distribution. In addition, the output power and external quantum efficiency under a 20-mA injection current are increased by 22% and 26.5%, respectively. Experimental and simulation results indicate that a multi-layer stacking structure can alleviate the current crowding effect in four ways: (1) a reduction in dislocation density; (2) replacement of quasi-two-dimensional electron transport with electronic bulk transport to enhance electron mobility; (3) an increase in electron concentration without improving the impurity concentration; and (4) a weakening of the electron scattering effect by reducing the impurity concentration.

Three-dimensional pompon-like Au/ZnO porous microspheres as solid phase microextraction coating for determination of volatile fatty acids from foot odor.

In this study, facile fabrication of three-dimensional (3D) pompon-like gold/zinc oxide (Au/ZnO) porous microspheres by hydrothermal procedure was investigated. These microspheres were utilized as solid phase microextraction (SPME) coating for determination of volatile fatty acids (VFAs) from foot odor coupling with gas chromatography-mass spectrometry (GC-MS). SEM and TEM characterizations showed that as-prepared material was composed of 1D porous nanowires and presented a uniform coating on stainless-steel wire. The extraction of VFAs including propanoic acid, butyric acid, isobutanoic acid, isovaleric acid, hexanoic acid, and heptylic acid was carried out by headspace model after sampling from human foot using cotton wool strips. Following optimization of extraction parameters including extraction temperature and time and desorption temperature and time, the as-prepared SPME coating presented better extraction efficiency than commercial DVB/CAR/PDMS fiber towards all the VFAs due to its excellent properties. Under the optimized conditions, the method exhibited good linearity (0.5-200 ng) with regression coefficients (R2) ranging from 0.9836 to 0.9981 for all the analytes. The limits of detection ranged from 0.017 to 0.098 ng. Single fiber repeatability varied from 6.5% to 11.2% and the fiber-to-fiber reproducibility ranged from 8.6% to 12.3%. The proposed method was successfully applied for extraction and determination of VFAs from foot odor after sampling using cotton wool strips.

Enhanced P-Type GaN Conductivity by Mg Delta Doped AlGaN/GaN Superlattice Structure.

A method of combining the AlGaN/GaN superlattices and Mg delta doping was proposed to achieve a high conductivity p-type GaN layer. The experimental results provided the evidence that the novel doping technique achieves superior p-conductivity. The Hall-effect measurement indicated that the hole concentration was increased by 2.06 times while the sheet resistivity was reduced by 48%. The fabricated green-yellow light-emitting diodes using the achieved high conductivity p-type GaN layer showed an 8- and 10-times enhancement of light output power and external quantum efficiency, respectively. The subsequent numerical calculation was conducted by using an Advanced Physical Model of Semiconductor Device to reveal the mechanism of enhanced device performance. This new doping technique offers an attractive solution to the p-type doping problems in wide-bandgap GaN or AlGaN materials.

Investigation of AlGaN/GaN Heterostructures Grown on Sputtered AlN Templates with Different Nucleation Layers.

In this work, a sputtered AlN template is employed to grow high-quality AlGaN/GaN heterostructures, and the effects of AlN nucleation layer growth conditions on the structural and electrical properties of heterostructures are investigated in detail. The optimal growth condition is obtained with composited AlN nucleation layers grown on a sputtered AlN template, resulting in the smooth surface morphology and superior transport properties of the heterostructures. Moreover, high crystal quality GaN material with low dislocation density has been achieved under the optimal condition. The dislocation propagation mechanism, stress relief effect in the GaN grown on sputtered AlN, and metal organic chemical vapor deposition AlN nucleation layers are revealed based on the test results. The results in this work demonstrate the great potential of AlGaN/GaN heterostructures grown on sputtered AlN and composited AlN nucleation layers for microelectronic applications.