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Structural and electrical properties of Pd/p-GaN contacts for GaN-based laser diodes
摘要： In this paper, the properties of Pd-based p-contacts on GaN-based laser diodes are discussed. Pd is often the metal of choice for ohmic contacts on p-GaN. However, for Pd/p-GaN ohmic contacts, nanovoids observed at the metal/semiconductor interface can have a negative impact on reliability and also reproducibility. The authors present a thorough analysis of the microstructure of the Pd/p-GaN interface by x-ray photoelectron spectroscopy (XPS) and scanning transmission electron microscopy (STEM). STEM data show that the microvoids at the p-GaN/Pd interface form during rapid thermal annealing. A combination of the following effects is suggested to support the void formation: (1) the differences in thermal expansion coefficients of the materials; (2) excess matrix or impurity atoms in the semiconductor, at the interface, and in the metals, which are released as gases; and (3) the strong antisurfactant effect of Pd on Ga-rich p-GaN surfaces. A slow temperature ramp during contact annealing reduces the formation of voids likely by suppressing the accumulation of gases at the interface. XPS data show that the Ga/N ratio can be reduced by suitable cleaning of the p-GaN surface, which enhances Pd adhesion. As a result, the quality of the contact system is improved by the systematic optimization of the surface cleanliness as well as the annealing parameters, leading to void-free and clean Pd/p-GaN interfaces. The specific contact resistance, extracted from linear transmission line method measurements, is reduced by an order of magnitude to 2 × 10?3 Ω cm2 at 1 mA for the same epitaxial layer stack.
关键词： Pd/p-GaN contacts,STEM,nanovoids,ohmic contacts,rapid thermal annealing,XPS,GaN-based laser diodes
更新于2025-09-23 15:21:01
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Improved Performance of Thermally Evaporated Sb2Se3 Thin-Film Solar Cells via Substrate-Cooling-Speed Control and Hydrogen-Sulfide Treatment
摘要： Antimony selenide is a promising abundant absorber material for solar cells. However, current Sb2Se3 photovoltaic devices, which are fabricated via thermal evaporation, tend to have stoichiometric problems and show suboptimal performance. In this paper, we use a modified thermal evaporator to fabricate high-quality Sb2Se3 films. By dedicatedly cooling the substrate, we can improve both the Sb2Se3 morphology and the Sb2Se3/CdS heterojunction interface substantially. We find a suitable annealing atmosphere, H2S, which can largely compensate for possible deficiencies of Se and remove the antimony-oxide layer on the film surface. Thanks to cooling control and H2S treatment, we obtain a significantly improved efficiency (6.24%) for the Sb2Se3 solar cells. Our results indicate that this thermal evaporation technique is a promising approach to improve the large-scale fabrication of antimony chalcogenide solar cells.
关键词： Thermal evaporation,Sb2Se3,Hydrogen-sulfide,Large-scale,Post-annealing process
更新于2025-09-23 15:21:01
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Solving the Laser Cutting Path Problem Using Population-Based Simulated Annealing with Adaptive Large Neighborhood Search
摘要： This paper presents an alternative algorithm for solving the laser cutting path problem which was modeled as Generalized Traveling Salesman Problem (GTSP). The objective is to minimize the traveling distance of laser cutting of all profiles in a given layout, where a laser beam makes a single visit and then does the complete cut of individual profile in an optimum sequence. This study proposed a hybrid method combining population-based simulated annealing (SA) with an adaptive large neighborhood search (ALNS) algorithm to solve the cutting path problem. Recombination procedures were executed alternately using swap, reversion, insertion and removal-insertion through a fitness proportionate selection mechanism. In order to reduce the computing time and maintain the solution quality, the 35% proportion of population were executed in each iteration using the cultural algorithm selection method. The results revealed that the algorithm can solve several ranges of problem size with an acceptable percentage of error compared to the best known solution.
关键词： ALNS,GTSP,Laser cutting path,Cultural algorithm,Simulated annealing
更新于2025-09-23 15:21:01
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Silicon nanocrystal hybrid photovoltaic devices for indoor light energy harvesting
摘要： Silicon nanocrystals (SiNCs) featuring size-dependent novel optical and electrical properties have been widely employed for various functional devices. We have demonstrated SiNC-based hybrid photovoltaics (SiNC-HPVs) and proposed several approaches for performance promotion. Recently, owing to the superiorities such as low power operation, high portability, and designability, organic photovoltaics (OPVs) have been extensively studied for their potential indoor applications as power sources. SiNCs exhibit strong light absorption below 450 nm, which is capable of sufficient photocurrent generation under UV irradiation. Therefore, SiNC-HPVs are expected to be preferably used for energy harvesting systems in indoor applications because an indoor light source consists of a shorter wavelength component below 500 nm than solar light. We successfully demonstrated SiNC-HPVs with a PCE as high as 9.7%, corresponding to the output power density of 34.0 mW cm?2 under standard indoor light irradiation (1000 lx). In addition, we have found that SiNC defects working as electron traps influence the electrical properties of SiNCs substantially, a thermal annealing process was conducted towards the suppression of defects and the improvement of the SiNC-HPVs performance.
关键词： Silicon nanocrystals,Power conversion efficiency,Indoor light energy harvesting,Thermal annealing,Hybrid photovoltaics
更新于2025-09-23 15:21:01
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Near Infrared Lasera??Annealed IZO Flexible Device as a Sensitive H2S Sensor at Room Temperature
摘要： A metal-oxide material (indium zinc oxide [IZO]) device with near-infrared (NIR) laser annealing was demonstrated on both glass and bendable plastic substrates (polycarbonate, polyethylene, and polyethylene terephthalate). After only 60 s, the sheet resistance of IZO films annealed with a laser was comparable to that of thermal-annealed devices at temperatures in the range of 200°C–300°C (1 hr). XPS, ATR, and AFM were used to investigate the changes in the sheet resistance and correlate them to the composition and morphology of the thin film. Finally, the NIR laser-annealed IZO films were demonstrated to be capable of detecting changes in humidity and serving as a highly sensitive gas sensor of hydrogen sulfide (in parts-per-billion concentration), with room-temperature operation on a bendable substrate.
关键词： IZO,sol-gel,laser annealing,NIR,gas sensor,flexible
更新于2025-09-23 15:21:01
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Brazing, Laser, and Electron-Beam Welding of Additively Manufactured GRCop-84 Copper for Phased Array Lower Hybrid Launchers
摘要： Recent advances in selective laser melting 3-D printing technology allow additive manufacturing of lower hybrid current drive (LHCD) RF launchers from a new material, Glenn Research Copper 84 (GRCop-84), a Cr2Nb (8 at. % Cr, 4 at. % Nb) precipitation hardened alloy, in configurations unachievable by conventional machining. Cr2Nb crystals pin grain boundaries within the copper matrix resulting in high tensile strength and resistance to annealing at elevated temperatures. Brazing, laser, and electron-beam welding (EBW) techniques are explored for joining a thin-walled GRCop-84 waveguide with zero porosity and minimal internal surface roughness. GRCop-84 wets well with the silver solder, CuSil, and Cusil-ABA brazes, once the durable surface oxide is mechanically removed. GRCop-84 melt pool size and flow during EBW is reduced compared to oxygen-free copper (OFC). Pulsed laser and e-beam welding maintains the Cr2Nb precipitate size; precipitate coarsening occurs in conduction mode e-beam welding.
关键词： joining processes,fusion reactor design,magnetic confinement,Annealing,tokamaks,copper alloys,melt processing,materials processing,phased arrays,waveguide
更新于2025-09-23 15:21:01
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On the Formation of Amorphous Ge Nanoclusters and Ge Nanocrystals in GeSixOy Films on Quartz Substrates by Furnace and Pulsed Laser Annealing
摘要： Nonstoichiometric GeO0.5[SiO2]0.5 and GeO0.5[SiO]0.5 germanosilicate glassy films are produced by the high-vacuum coevaporation of GeO2 and either SiO or SiO2 powders with deposition onto a cold fused silica substrate. Then the films are subjected to furnace or laser annealing (a XeCl laser, λ = 308 nm, pulse duration of 15 ns). The properties of the samples are studied by transmittance and reflectance spectroscopy, Raman spectroscopy, and photoluminescence spectroscopy. As shown by analysis of the Raman spectra, the GeO[SiO] film deposited at a substrate temperature of 100°C contains amorphous Ge clusters, whereas no signal from Ge–Ge bond vibrations is observed in the Raman spectra of the GeO[SiO2] film deposited at the same temperature. The optical absorption edge of the as-deposited GeO[SiO2] film corresponds to ~400 nm; at the same time, in the GeO[SiO] film, absorption is observed right up to the near-infrared region, which is apparently due to absorption in Ge clusters. Annealing induces a shift of the absorption edge to longer wavelengths. After annealing of the GeO[SiO2] film at 450°C, amorphous germanium clusters are detected in the film, and after annealing at 550°C as well as after pulsed laser annealing, germanium nanocrystals are detected. The crystallization of amorphous Ge nanoclusters in the GeO[SiO] film requires annealing at a temperature of 680°C. In this case, the size of Ge nanoclusters in this film are smaller than that in the GeO[SiO2] film. It is not possible to crystallize Ge clusters in the GeO[SiO] film. It seems obvious that the smaller the semiconductor nanoclusters in an insulating matrix, the more difficult it is to crystallize them. In the low-temperature photoluminescence spectra of the annealed films, signals caused by either defects or Ge clusters are detected.
关键词： crystallization,pulsed laser annealing,germanosilicate glasses,germanium nanoclusters
更新于2025-09-23 15:21:01
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Highly Efficient All-Small-Molecule Organic Solar Cells with Appropriate Active Layer Morphology by Side Chain Engineering of Donor Molecules and Thermal Annealing
摘要： It is very important to fine-tune the nanoscale morphology of donor:acceptor blend active layers for improving the photovoltaic performance of all-small-molecule organic solar cells (SM-OSCs). In this work, two new small molecule donor materials are synthesized with different substituents on their thiophene conjugated side chains, including SM1-S with alkylthio and SM1-F with fluorine and alkyl substituents, and the previously reported donor molecule SM1 with an alkyl substituent, for investigating the effect of different conjugated side chains on the molecular aggregation and the photophysical, and photovoltaic properties of the donor molecules. As a result, an SM1-F-based SM-OSC with Y6 as the acceptor, and with thermal annealing (TA) at 120 °C for 10 min, demonstrates the highest power conversion efficiency value of 14.07%, which is one of the best values for SM-OSCs reported so far. Besides, these results also reveal that different side chains of the small molecules can distinctly influence the crystallinity characteristics and aggregation features, and TA treatment can effectively fine-tune the phase separation to form suitable donor–acceptor interpenetrating networks, which is beneficial for exciton dissociation and charge transportation, leading to highly efficient photovoltaic performance.
关键词： small molecule donor materials,all-small-molecule organic solar cells,interpenetrating networks,side-chain engineering,thermal annealing
更新于2025-09-23 15:21:01
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Molecular Simulations of Laser Spike Annealing of Block-Copolymer Lamellar Thin-Films
摘要： We use molecular dynamic simulations to study the phase behavior of a coarse-grained lamella-forming A-b-B di-block copolymer under thin-film soft confinement for different heating cycle lengths, film thicknesses, and substrate-polymer affinities. This model describes the effect on thin-film morphology with a free surface (air-polymer interface) and a solid substrate. Our simulation results were first validated by showing that they capture changes for the order-disorder transition temperature with annealing conditions consistent with those found in laser spike annealing experiments, when the vertical lamella phase formed on neutral substrates. In addition, simulations with a substrate selective for a particular block revealed the formation of other phases including a mixed vertical-horizontal lamella and a metastable island phase having horizontal but incomplete lamella layers. The nanoscale roughness features of this island phase, and hence its surface wettability, can be tuned with suitable choices of chemistry and annealing conditions.
关键词： thin-film,nanoscale roughness,order-disorder transition,phase behavior,laser spike annealing,molecular dynamic simulations,block copolymer
更新于2025-09-23 15:21:01
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A Thermally Induced Perovskite Crystal Control Strategy for Efficient and Photostable Widea??Bandgap Perovskite Solar Cells
摘要： Wide-bandgap perovskite solar cells (WBG PSCs) have gained attention as promising tandem partners for silicon solar cells due to their complementary absorption, superb open-circuit voltage, and easy solution process. Recently, both their performance and stability have been improved by compositional-engineering or defect-passivation strategies, due to modulation of perovskite crystal size and reduction of crystal defects. In this work, we report a thermally induced phase control (TIPC) strategy, which enables efficient and photostable WBG PSCs without any compositional engineering by exploring a thermal annealing process window of WBG perovskite films for the annealing temperature and time range of 100-175°C and 3-60 minutes, respectively. Within this window, we found a key annealing regime that produces preferred crystal orientations of lead iodide and the WBG perovskite, suppressing phase segregation and reducing charge recombination in the perovskites. The WBG PSC (composition of FA0.75MA0.15Cs0.1PbI2Br and Eg of 1.73 eV) optimized by TIPC exhibited an excellent power conversion efficiency (PCE) of 18.60% and improved operational stability, maintaining >90% of the maximum PCE (during maximum power point tracking) without encapsulation after 12-hour operation under AM 1.5G irradiation in ambient air conditions and after 500-hour operation under white LED irradiation (100 mW cm-2) in inert N2 gas conditions.
关键词： wide-band gap perovskite,thermal annealing process,operational stability,perovskite solar cells,invariant bandgap
更新于2025-09-23 15:21:01