High-quality Layers Research Articles

Deep level defects in low-pressure chemical vapor deposition grown (010) β-Ga2O3

This study provides the full-bandgap evaluation of defect state distributions in beta phase gallium oxide (β-Ga2O3) grown by low-pressure chemical vapor deposition (LPCVD) on (010) β-Ga2O3 substrates at high growth of up to 20 µm/h. Deep-level optical spectroscopy and deep-level transient spectroscopy measurements applied to Ni/β-Ga2O3 Schottky diodes revealed the presence of a previously unreported defect state at EC-3.6 eV, which dominated the overall trap distribution in LPCVD grown material. However, states at EC-0.8 eV, EC-2.0 eV, and EC-4.4. eV were also detected, similar to prior studies on β-Ga2O3 grown by other methods, with similar or lower concentrations for the LPCVD samples. The EC-0.8 eV and EC-2.0 eV states were previously connected to residual Fe impurities and gallium vacancies, respectively. The total concentration of traps in the LPCVD material was on par with or lower than the state-of-the-art metal–organic chemical vapor deposition-grown materials despite the much higher growth rate, and the distribution of states showed negligible dependence on SiCl4 flow rate and doping concentration. These results demonstrate that the high growth rate of LPCVD-grown β-Ga2O3 is very promising for achieving thick, low defect density, and high-quality layers needed for multi-kV device applications.

Very Low Temperature Tensile and Selective Si:P Epitaxy for Advanced CMOS Devices

We demonstrate the feasibility of selectively growing highly doped and tensile-strained Si:P layers at temperatures 500°C or less on each side of advanced n-type MOS devices. To that end, we used a Cyclic Deposition Etch (CDE) strategy instead of a conventional “co-flow” approach fit for the high temperature (> 600°C) Selective Epitaxial Growth (SEG) of t-SiP films. A high order silicon precursor was used together with PH3 to benefit from high t-Si:P growth rates at 500°C and less. Selective etchings were performed with Cl2 as an etchant gas, as it yielded much higher etch rates than HCl. We first investigated the blanket growth of t-SiP on fullsheet Si wafers. 5 to 15 times higher higher growth rates than with standard precursors were obtained at low temperatures with our new HOS silicon precursor. We then investigated the etching efficiency of Cl2, with several tens of nanometers per minutes etch rates achieved at very low temperatures. Using a CDE strategy, we then probed phosphorus incorporation in blanket t-Si:P films on fullsheet wafers. High quality and smooth t-SiP layers with up to 5.4%, 4.3% and 5.8% of P and sheet resistances as low as 0.33, 0.27 and 0.21 mohm.cm were obtained at 500°C, 475°C and 450°C, respectively. We then tested our CDE SiP process for SEG, first on test structures then on each side of real FD-SOI devices, with smooth, high quality, tensile SiP layers grown at 500°C with 4.5% of P.

Fabrication and performance analysis of high-performance cylindrical ionic polymer-metal composite actuators with various diameters

Ionic polymer-metal composites (IPMCs) are electroactive polymer actuators that have been used as artificial muscles and have broad application prospects. In order to further improve the actuation performance of cylindrical IPMCs, Nafion rods with different diameters were prepared by extrusion process, and cylindrical IPMCs with high-quality Pt electrode layers were prepared by electroless plating in this study. The electrochemical properties and actuation performance of cylindrical IPMCs with various diameters were investigated. The tests show that the prepared cylindrical IPMCs have excellent electromechanical properties. As diameter increases, the blocking force and counter back-relaxation ability both increase significantly. Furthermore, the IPMCs with diameter of 3.0 mm under a DC voltage exhibits a superior blocking force (323.9 mN) and excellent power density (up to 139.41 W m−3). Moreover, the thick cylindrical IPMC can lift objects 400 times its weight, demonstrating exceptional load capacity, which shows great prospect of realizing artificial muscles.

Enhanced device performance of Cs2AgBiBr6 double perovskite photodetector by SnO2/ZnO double electron transport layer

In this study, we report the enhancement of device performance in a lead-free perovskite Cs2AgBiBr6-based deep blue photodetector by using a SnO2/ZnO double electron transport layer (ETL). The SnO2 layer was inserted to minimize the energy loss at the interface between the ZnO ETL and perovskite absorber layer by preparation of a smooth perovskite film. The hydrophilic SnO2 layer coating on the hydrophobic ZnO nanorods provides a uniform and high-quality perovskite layer without pinholes. Reduced contact angle measurement confirmed that the surface property changes towards hydrophilicity after insertion of a SnO2/ZnO double ETL compared with bare ZnO nanorods. Moreover, the introduction of the SnO2 layer leads to better carrier transportation and extraction by matching the energy level between the perovskite and ZnO ETL. The pinhole-free perovskite film and a well-matched energy level are responsible for the Cs2AgBiBr6-based visible photodetector with a SnO2/ZnO double ETL demonstrating simultaneous improvement of responsivity and specific detectivity by 12.7 times and 16.5 times, respectively, compared with those of the ZnO single ETL. From our results, we can suggest a guideline for an interface engineering strategy to improve perovskite optoelectronic device performance.

Reduced Dislocation of GaAs Layer Grown on Ge-Buffered Si (001) Substrate Using Dislocation Filter Layers for an O-Band InAs/GaAs Quantum Dot Narrow-Ridge Laser.

The development of the low dislocation density of the Si-based GaAs buffer is considered the key technical route for realizing InAs/GaAs quantum dot lasers for photonic integrated circuits. To prepare the high-quality GaAs layer on the Si substrate, we employed an engineered Ge-buffer on Si, used thermal cycle annealing, and introduced filtering layers, e.g., strained-layer superlattices, to control/reduce the threading dislocation density in the active part of the laser. In this way, a low defect density of 2.9 × 107 cm−2 could be achieved in the GaAs layer with a surface roughness of 1.01 nm. Transmission electron microscopy has been applied to study the effect of cycling, annealing, and filtering layers for blocking or bending threading-dislocation into the InAs QDs active region of the laser. In addition, the dependence of optical properties of InAs QDs on the growth temperature was also investigated. The results show that a density of 3.4 × 1010 InAs quantum dots could be grown at 450 °C, and the photoluminescence exhibits emission wavelengths of 1274 nm with a fullwidth at half-maximum (FWHM) equal to 32 nm at room temperature. The laser structure demonstrates a peak at 1.27 μm with an FWHM equal to 2.6 nm under a continuous-wave operation with a threshold current density of ∼158 A/cm2 for a 4-μm narrow-ridge width InAs QD device. This work, therefore, paves the path for a monolithic solution for photonic integrated circuits when III−V light sources (which is required for Si photonics) are grown on a Ge-platform (engineered Ge-buffer on Si) for the integration of the CMOS part with other photonic devices on the same chip in near future.

Study of the Preparation of Micronized Zinc Phosphate Dihydrate with Potential for Application in the Phosphating Process

The protection of metal parts against corrosion damage is one of the most comprehensive areas of industrial chemistry and a wide range of methods exists to protect the surface from corrosive stimulators, including phosphating. A key phosphating process, the tricationic phosphating, consists of baths containing zinc dihydrogen phosphate and other cations, such as Zn2+, Co2+, Ni2+ or Mg2+. However, cobalt and nickel ions are classified as environmentally harmful and they are being actively excluded from industrial processes. The use of sufficiently micronized zinc phosphate dihydrate (µ-Zn3(PO2)2 · 2H2O) is one the possible approaches to significantly reduce or eliminate heavy metals from the phosphating process. The micronized zinc phosphate dihydrate serves as a nucleus on the metal surface to form a sufficiently high-quality phosphate layer. The study aims to find a procedurally optimal dispersion methodology suitable for application in the Czech Republic. The use of progressive grinding methods such as the jet mills is emphasized and shows promising results.

Fully Textured, Production-Line Compatible Monolithic Perovskite/Silicon Tandem Solar Cells Approaching 29% Efficiency.

Perovskite/silicon tandem solar cells are promising avenues for achieving high-performance photovoltaics with low costs. However, the highest certified efficiency of perovskite/silicon tandem devices based on economically matured silicon heterojunction technology (SHJ) with fully textured wafer is only 25.2% due to incompatibility between the limitation of fabrication technology which is not compatible with the production-line silicon wafer. Here, a molecular-level nanotechnology is developed by designing NiOx /2PACz ([2-(9H-carbazol-9-yl) ethyl]phosphonic acid) as an ultrathin hybrid hole transport layer (HTL) above indium tin oxide (ITO)recombination junction, to serve as a vital pivot for achieving a conformal deposition of high-quality perovskite layer on top. The NiOx interlayer facilitates a uniform self-assembly of 2PACz molecules onto the fully textured surface, thus avoiding direct contact between ITO and perovskite top-cell for a minimal shunt loss. As a result of such interfacial engineering, the fully textured perovskite/silicon tandem cells obtain a certified efficiency of 28.84% on a 1.2-cm2 masked area, which is the highest performance to date based on the fully textured, production-line compatible SHJ. This work advances commercially promising photovoltaics with high performance and low costs by adopting a meticulously designed HTL/perovskite interface.

OPTIMASI PARAMETER KARBURISASI TEMPERATUR RENDAH PADA BAJA TAHAN KARAT AUSTENITIK MENGGUNAKAN METODE TAGUCHI

Austenitic stainless steel is a popular material for its corrosion resistant properties, however it has low hardness which limits its application. Low-temperature carburizing can be used to improve the mechanical properties of the austenitic stainless steel by producing expanded austenite layer. In order to get a high-quality layer and an efficient processing operation, the carburizing process must be optimized. In this research, a Taguchi method was utilized to investigate the effect of processing parameters related to the formation of the expanded austenite layer depth in austenitic stainless steel. Four factors were selected to be optimized namely temperature, gas flow rate, time, and gas composition with three levels each. L9(34) orthogonal array was applied with nine experimental tests to get the diffusion depth value of carbon in the expanded austenite layer. S/N ratio was used to determine the optimum factor combination with nominal-the-better quality characteristic and the most significant factor was obtained by applying the Analysis of Variance. Temperature was found to be the most significant factor with 54.91% contribution. The optimum combination was also successfully defined with temperature at 450°C (level 2), gas flow rate at 15 liter per minute (level 2), time at 12 hours (level 3), and gas composition at 15% CH4 – 5% H2 – 80% N2 (level 3). Clearly, in this study the Taguchi method was proven to be appropriately used as one of robust tools in optimizing the thermochemical treatment process parameters.

High Voltage Normally-Off p-GaN Gate HEMT with the Compatible High Threshold and Drain Current

In this paper, we demonstrate a high voltage normally-off p-GaN gate high-electron-mobility-transistor (HEMT) to realize the compatible high threshold voltage (V TH) and high drain current (I D) performance. With the optimization of the epitaxial structure, the presented device shows a significantly improved V TH. Meanwhile, by using the high-quality ALD-Al2O3 passivation layer, the high I D is also realized in the device because of the access region resistance reduction. Supported by the device fabrication, the p-GaN gate HEMT delivers a V TH = 3.2 V measured by linear extrapolation, a relatively large saturation I D (I D_SAT) of 246 mA mm−1, and a high breakdown voltage (BV) of 1830 V at 1 mA mm−1. Among various p-GaN gate HEMTs with the I D_SAT over 200 mA mm−1, the fabricated p-GaN gate HEMT has a competitive V TH. The results suggest that the proposed device could be a promising candidate in high V TH and I D power electronics.

Li-Doped SnO<sub>2</sub> Electron Transport Layer for High-Performance Perovskite Solar Cell Fabricated Using Magnetic Field-Assisted Electrodeposition

One of the key challenges for the development of perovskite solar cells lies in the approach toward large-scale fabrication of the active materials that allows for good photovoltaic performance, as well as facile handling. The electrodeposition technique can potentially address such requirements. However, the technique has yet to be investigated in detail and still suffers from low efficiency of the device. In this study, we sought to significantly upgrade the electrodeposition approach by coupling the technique with an external magnetic field in the preparation of high-quality PbI2 precursor layer and using Li-doped SnO2 electron transport layer. Our results showed that the magnetic field-assisted electrodeposition yielded good crystallinity of PbI2 and perovskite. Introducing the Li-doped mesoporous SnO2 into the device structure resulted in a higher current density of 18.50–18.80 mA cm-2, which can be attributed to, based on the linear sweep voltammetry, reduced resistance of the electron transport layer from 32.27 to 22.11 Ω cm-2. Moreover, the carbon-based device prepared using this simple procedure also yielded 5.20% in photoconversion efficiency for 1-cm2 active area and 0.45% for 25-cm2 active area, all without any significant hysteresis.

A study on MOCVD growth window for high quality N-polar GaN for vertical device applications

Lateral N-polar GaN devices have outperformed Ga-polar GaN counterparts in mm-wave applications. A vertical N-polar GaN device structure with higher breakdown voltage is expected to further improve the output power density. This paper is aimed at understanding the growth conditions for such a vertical N-polar GaN device stack. A vertical device stack requires high-quality n-GaN layer with low unintentional dopant concentration and high electron mobility for better ON resistance–breakdown voltage performance. A systematic study by varying reactor temperature, pressure and NH3 flow rate is performed in the metal organic chemical vapor deposition growth of N-polar GaN for vertical device structure. Structural quality of the sample is increased with increase growth temperature and higher NH3 flow rate, yet an increase in surface roughness is observed for highest temperature used. The N-polar GaN grown at the optimized conditions exhibited a x-ray diffraction rocking curve full width half maximum of symmetric (0002) and skew-symmetric (20 ) scans of 358″ and 569″ respectively with a low oxygen and carbon concentration of 6 × 1016 cm−3 and 5 × 1016 cm−3, respectively. The optimized sample exhibited a low screw dislocation density of 2.5 × 108 cm−2 on sapphire substrate. A gradual increase in the bulk mobility of electrons with decrease in screw dislocation density in N-polar GaN is also reported.

Optimization of electrodeposition time on the properties of Cu2ZnSnS4 thin films for thin film solar cell applications

The Electrochemical deposition was used to create a quaternary CZTS (Cu2ZnSnS4) kesterite thin layer. An aqueous solution of CZTS was used to deposit a thin layer over Indium Tin Oxide. The effects of deposition time (variation) on CZTS thin films under ambient conditions were investigated in this study. Several available characterization systems were used to study the samples as they were produced. The polycrystalline description of the layer is investigated by X-ray diffraction. The SEM as well as AFM study show that the deposition time improved surface morphology and topography of CZTS thin films which increase several nm in grain size. Furthermore, depending upon the deposition duration that affect the thickness and crystallinity of the films prepared, the optical study reveals an acceptable band gap in a range of 1.71–1.42 eV. Characteristics of high-quality CZTS absorber layers for solar cell applications are determined by deposition time variation. To check the effect of this band gap variation (1.71–1.42 eV, depending upon the deposition time) on the performance of a CZTS based thin film solar cell, a simulation software SCAPS-1D is being used.

Highly Efficient Self-Encapsulated Flexible Semitransparent Perovskite Solar Cells via Bifacial Cation Exchange.

Flexible semitransparent perovskite solar cells (ST-PSCs) have great potential for use in high-density energy systems, such as building or vehicle integrated photovoltaics, considering the great features of PSC devices, including high performance, light weight, thin-film processability, and high near-infrared transmittance. Despite numerous efforts toward achieving efficiency and flexibility in ST-PSCs, the realization of high-performance and operational stability in ST-PSCs still require further development. Herein, we demonstrated the development of highly efficient, stable, and flexible ST-PSCs using polyimide-integrated graphene electrodes via a lamination-assisted bifacial cation exchange strategy. A high-quality perovskite layer was obtained through the cation exchange reaction using the lamination process, and ST-PSCs with 15.1% efficiency were developed. The proposed ST-PSC device also demonstrated excellent operational stability, mechanical durability, and moisture stability owing to the chemically inert and mechanically robust graphene electrodes. This study provides an effective strategy for developing highly functional ST-perovskite optoelectronic devices with high-performance and long-term operational stability.

The straightforward fabrication of thin silicide layers at low temperatures by employing the molecular-incident reaction effect

Because of the ease of formation, and good lattice match with Si, metal silicides often form high-quality epitaxial layers and have established themselves over the years as important technological materials with industrial applications. For the fabrication of silicon-based devices, the contact between metal electrodes and Si is a key issue. The properties of thin films on silicon substrates are strongly dependent on their microstructure and local chemistry. However, a concrete understanding of the influence of a silver layer on different transition metal/silicon interfaces is not currently available. We propose, for the first time, a new model called molecular-incident reaction effect (MoIRE) model that successfully explains the different chemical reactions for Co/Si and Ni/Si interfaces by the introduction of a 3×3R30o-Ag layer. The interaction transfer of silicon atoms forms a Co silicide for Co/3×3R30o-Ag/Si(111) with a thickness of a few nanometers, thus greatly reducing the temperature needed for the formation of a layered CoSi2 silicide compared to that for typical CoSi2 silicide formation at a Co/Si interface. Based on the MoIRE mechanism, the introduction of the 3×3R30o-Ag layer as an intermediate layer permits the silicidation temperature needed to produce a NiSi layer to be reduced to 400 K from typically above 600 K. This approach is advantageous for the formation of a silicide at the Ni/Si interface at low temperature. Based on the MoIRE model for silicide formation at Ni/3×3R30o-Ag/Si(111), we propose a technique for the synthesis Ni silicide layers at lower temperatures with simpler fabrication steps due to the difference in the properties between Co and Ni. This mechanism of low-temperature fabrication includes the formation of (1) a 3×3R30o-Ag and (2) a NiSi layer. The findings presented herein will be useful for more efficiently forming salicides in integrated circuit fabrication, as well as for developing superconducting circuits and quantum bits for quantum computing.

The fabrication of phytate and LDH-based hybrid nanosheet towards improved fire safety properties and superior smoke suppression of intumescent flame retardant LDPE

An effective fire retardant system was developed composed by traditional intumescent flame retardant (IFR) and a new-typed nano-synergist (PAMA-SDBS-LDH, P@L), and their synergistic effect and mechanism on the thermal stability and flammability properties of low-density polyethylene (LDPE) was comprehensively studied. Briefly, the nano-synergist was successfully prepared by using melamine, phytic acid and Zn-Ni-Al layered double hydroxide (LDH) according to hydrothermal method. By adding 0.5% PAMA-SDBS-LDH and 29.5% IFR, the fire retardant properties of LDPE composite (LDPE/I/P@L) reached V-0 rating in UL-94 test. The total smoke production of LDPE/I/P@L decreased by 69.8% compared with LDPE. It is confirmed that PAMA-SDBS-LDH nanosheet is an efficient synergist to promote the formation of high-quality char layer via multiple fire retarding mechanisms. The good mechanical properties of LDPE/IFR system are also maintained by incorporating PAMA-SDBS-LDH. Undoubtedly, this study will provide valuable insights into improving the fire retardant efficiency and practical application of traditional IFR.

Facile synthesis of cadmium phosphorus trisulfide nanosheets for highly efficient photocatalytic performance

With the rise of two-dimensional (2D) materials, layered metal thiophosphates (MPS3), as an important branch, have attracted much attention because of their excellent physical and chemical properties. Cadmium phosphorus trisulfide (CdPS3), as a promising photocatalyst, can be used for hydrogen evolution and organic degradation. Herein, high-quality 2D CdPS3 few layers are obtained by exfoliating bulk CdPS3 crystal. The optical properties of the as-obtained CdPS3 few layers show good light-harvesting ability, endowing it with excellent photocatalytic hydrogen evolution performance (10.88 mmol g−1 h−1) and high organic degradation performance (more than 92% within 30 min) under Xe lamp irradiation. This research provides opportunities for the preparation and application of other 2D MPS3 type materials in the field of photocatalysis.

Analyses of p–n heterojunction in 9.4%-efficiency CZTSSe thin-film solar cells: Effect of Cu content

Successful formation of the absorber layer is regarded as the most important step when fabricating Cu2ZnSn(S,Se)4 (CZTSSe) thin-film solar cells. A high-quality CZTSSe absorber layer can enhance the parameters of thin-film solar cells. We concentrated on analyzing the CZTSSe surface, which is directly related to forming the p-n junction. We made changes to the surface of the absorber layer by controlling the Cu content via the sputtering time. When the Cu content was insufficient, secondary phases and agglomerated metallic precursors appeared on top of the CZTSSe absorber layer. We analyzed the defects and secondary phases that could adversely affect the formation of the p-n junction by using energy-dispersive X-ray spectroscopy, X-ray diffractometer, and Raman spectroscopy. We also measured and calculated the electric parameters of CZTSSe thin-film solar cells to investigate the CZTSSe/CdS interface. The performance of a CZTSSe thin-film solar cell was enhanced and stabilized by optimizing the concentration of Cu in the absorber layer. Our results indicate the importance of the Cu ratio on the surface of the CZTSSe absorber layer as it affects the p-n junction in the CZTSSe thin-film solar cell. The highest photoconversion efficiency was 9.4% when the Cu component was optimized.

High-frequency acoustic cavitation in the technology of producing milk and dairy products

The article tells us about the issue of the influence of high-frequency acoustic cavitation on the quality characteristics of raw milk and white cheese produced with its use. It is shown that with the duration of milk processing for 30 minutes and the impact power of 45 kHz, the number of bacteria of the Escherichia coli group decreases by 40% and native calcium is preserved, which is subsequently necessary for the formation of a high-quality cheese layer. The effect of high-frequency acoustic cavitation on the components of milk, such as fat and protein, has been studied. It is established that during the initial period of exposure to high-frequency cavitation, there is a crushing of fat particles - homogenization with subsequent agglomeration, and then the release of free (destabilized) fat. It is worth noting that acoustic cavitation does not have a negative effect on the protein component of milk. Thus, whey proteins, which are most susceptible to denaturation (precipitation) during heat treatment, remain in the native state during cavitation exposure. The authors concluded that high-frequency acoustic exposure is technologically feasible in the production of high-protein products, in particular, in the production of white cheese. The results of histological analysis indicate that calcium in this type of processing in cheese has a structured appearance and larger associations in size compared to cheese obtained from unprocessed milk, which has a positive effect on the quality of the protein matrix of the product.

Electrodeposition of Equiatomic FePt Permanent Magnets from Non-Aqueous Electrolytes Based on Ethylene Glycol

The highly ordered L10 hard-magnetic phase of the equiatomic FePt alloy is of significant interest for a great number of applications, ranging from the realization of magnetic sensors to the deposition of thin layers for vertical recording. In this context, the development of wet deposition processes able to yield high-quality layers of FePt represents a need of considerable industrial relevance. While several aqueous-based electrodeposition approaches have been developed for the manufacturing of FePt, these formulations evidenced substantial technological limitations, specifically connected to the use of water as solvent. The present work describes the deposition of FePt from a non-aqueous electrolyte based on ethylene glycol, which presents potential advantages in terms of gas evolution reduction and purity improvement of the obtained coatings. Deposition was carried out using Fe(III) and Pt(IV) as precursors and ammonium chloride as additive to enhance the quality of the coatings and their compositional uniformity. In this way, equiatomic FePt thin films characterized by a good morphology were easily obtained. After annealing at 600 °C, their microstructure changed and the disordered fcc phase present in the as-plated alloy evolved into the highly magneto-crystalline anisotropic L10 phase. As a consequence, coercivity reached values in excess of 10 kOe.

Self-sacrifice alkali acetate seed layer for efficient four-terminal perovskite/silicon tandem solar cells

Seed-assisted growth is an effective way to achieve high-quality perovskite active layers for efficient and stable perovskite solar cells (PSCs). However, it is still challenging for conventional seed layers to realize the synergistic effect of the perovskite crystallization control and defect passivation without hindering the charge extraction and light absorption. Here, a self-sacrifice alkali acetate seed layer is employed at the buried perovskite interface to assist a vertical bottom–top growth of the high-quality perovskite film. Meanwhile, the dissolved alkali and acetate ions can diffuse into the perovskite layer, providing an efficient defect passivation and a favorable interfacial energy band alignment at both electron- and hole-selective contacts. As a result, these favorable synergistic effects enable the fabrication of a 21.69 % efficient PSC with a boosted fill factor of 83.33 % and enhanced long-term stability. Moreover, the optimized semitransparent perovskite solar cell (ST-PSC) achieves a certified efficiency of 19.28 %, the highest reported for p–i–n typed ST-PSCs. Combining the ST-PSC with a silicon bottom cell, the four-terminal perovskite/silicon tandem solar cell reaches a record efficiency of 28.28 %.