High-quality Substrates Research Articles

Acoustic Wave Filter Technology-A Review.

Today, acoustic filters are the filter technology to meet the requirements with respect to performance dictated by the cellular phone standards and their form factor. Around two billion cellular phones are sold every year, and smart phones are of a very high percentage of approximately two-thirds. Smart phones require a very high number of filter functions ranging from the low double-digit range up to almost triple digit numbers in the near future. In the frequency range up to 1 GHz, surface acoustic wave (SAW) filters are almost exclusively employed, while in the higher frequency range, bulk acoustic wave (BAW) and SAW filters are competing for their shares. Prerequisites for the success of acoustic filters were the availability of high-quality substrates, advanced and highly reproducible fabrication technologies, optimum filter techniques, precise simulation software, and advanced design tools that allow the fast and efficient design according to customer specifications. This paper will try to focus on innovations leading to high volume applications of intermediate frequency (IF) and radio frequency (RF) acoustic filters, e.g., TV IF filters, IF filters for cellular phones, and SAW/BAW RF filters for the RF front-end of cellular phones.

Epitaxial NixPd1-x (111) Alloy Substrates with Continuously Tunable Lattice Constants for 2D Materials Growth.

Epitaxial strain can be a powerful parameter for directing the growth of thin films. Unfortunately, conventional materials only offer discrete choices for setting the lattice strain. In this work, it is demonstrated that epitaxial growth of transition metal alloy solid solutions can provide thermally stable, high-quality growth substrates with continuously tunable lattice constants. Molecular beam epitaxy was used to grow NixPd1-x(111) alloy films with lattice constants between 3.61 and 3.89 Å on the hexagonal (0001) basal planes of α-Al2O3 and Cr2O3 (grown as epitaxial films on α-Al2O3 (0001)). The Cr2O3 acted as an adhesion layer, which not only improved the high-temperature stability of the films but also produced single-domain films with NixPd1-x [112̅] parallel to Cr2O3 [112̅0], in contrast to growth on α-Al2O3 that yielded twinned films. Surface characterization by electron diffraction and scanning tunneling microscopy (STM) as well as bulk X-ray diffraction analysis indicated that the films are suitable as inexpensive and stable substrates for thin-film growth and for surface science studies. To demonstrate this suitability, bilayer SiO2, a two-dimensional van der Waals material, was grown on a NixPd1-x(111) film tuned to closely match the film's lattice constant, with STM and electron diffraction results revealing a highly ordered, single-phase crystalline state.

Simulated Study on the Effects of Substrate Thickness and Minority-Carrier Lifetime in Back Contact and Back Junction Si Solar Cells

The BCBJ (Back Contact and Back Junction) or back-lit solar cell design eliminates shading loss by placing the pn junction and metal electrode contacts all on one side that faces away from the sun. However, as the electron-hole generation sites now are located very far from the pn junction, loss by minority-carrier recombination can be a significant issue. Utilizing Medici, a 2-dimensional semiconductor device simulation tool, the interdependency between the substrate thickness and the minority-carrier recombination lifetime was studied in terms of how these factors affect the solar cell power output. Qualitatively speaking, the results indicate that a very high quality substrate with a long recombination lifetime is needed to maintain the maximum power generation. The quantitative value of the recombination lifetime of minority-carriers, i.e., electrons in p-type substrates, required in the BCBJ cell is about one order of magnitude longer than that in the front-lit cell, i.e., 5 × 10−4 sec vs. 5 × 10−5 sec. Regardless of substrate thickness up to 150 μm, the power output in the BCBJ cell stays at nearly the maximum value of about 1.8 × 10−2 W·cm−2, or 18 mW·cm−2, as long as the recombination lifetime is 5 × 10−4 s or longer. The output power, however, declines steeply to as low as 10 mW·cm−2 when the recombination lifetime becomes significantly shorter than 5 × 10−4 sec. Substrate thinning is found to be not as effective as in the front-lit case in stemming the decline in the output power. In view of these results, for BCBJ applications, the substrate needs to be only mono-crystalline Si of very high quality. This bars the use of poly-crystalline Si, which is gaining wider acceptance in standard front-lit solar cells.

Hydraulic Performance of Horticultural Substrates—2. Development of an Evaluation Framework

Sustainable, environmentally friendly and resource-saving water and nutrient management in horticulture requires knowledge of the hydraulic suitability of horticultural substrates for each specific application. The aim of this study was to develop methods and a rating framework to assess the hydraulic performance of horticultural substrates. The hydraulic criteria related to high-quality horticultural substrates were defined as the amount of easily plant-available water (EAW) in the tension range between 10 and 100 hPa, the air capacity and the height of capillary rise. Limiting factors could be water repellency effects and shrinkage. The rating framework consisted of 5 classes between non-satisfactory and very good. The assessment of the hydraulic performance was split for the cultivation into 10-, 20-, and 30-cm-high containers. It was tested on 18 commercial substrates. More than 70% of the tested substrates revealed scores between very good and good. About 30% were evaluated as medium or satisfactory. The most critical aspect was the low air capacity in shallow containers. Shrinkage and water repellency sometimes strongly diminished the score. Both the measurement methods for quantifying substrate hydraulic properties and the evaluation procedure proved applicable. The impact of different ingredients and the composition of substrates of their hydraulic performance should be statistically analysed in further studies.

Unraveling bulk defects in high-quality c-Si material via TIDLS

The current trend in silicon photovoltaics moving towards high-quality thin mono-crystalline silicon substrates sets a new challenge for the understanding of recombination mechanisms limiting the final performance of solar cells. Temperature- and injection-dependent lifetime spectroscopy (TIDLS) has been shown to be a promising method for studying of high-quality material with lifetime above 10 ms where the concentration of electrically active defects is well below the sensitivity of the most well-known characterization techniques. In particular, when coupled with the Shockley–Read–Hall lifetime recombination model, TIDLS is capable of providing the most important defects' parameters including their energy level and concentration. In this contribution, we show that for a high-quality silicon material, a thorough evaluation of the surface recombination velocity (SRV) temperature- and injection dependence is crucial for an accurate identification of the defects contained in the bulk. A new methodology for the analysis of TIDLS data, called defect parameters contour mapping, is introduced for the first time. By applying it to high-quality n-type float zone c-Si samples passivated by a-Si:H(i) or an a-Si:H(i)/a-Si:H(n) stack, we are able to assert the presence of defects in high lifetime materials in a range of concentration unachievable by any other characterization technique thus far. Copyright © 2016 John Wiley & Sons, Ltd.

Process control model for growth rate of molecular beam epitaxy of MgO (111) nanoscale thin films on 6H-SiC (0001) substrates

Magnesium oxide (MgO) is a good candidate for an interface layer in multifunctional metal-oxide nanoscale thin-film heterostructures due to its high breakdown field and compatibility with complex oxides through O bonding. In this research, molecular beam epitaxy (MBE) is used to deposit 10 nm to 15 nm MgO single-crystal films on silicon carbide with hexagonal polytype 6H (6H-SiC) to serve as an interface layer for effective integration of functional oxides. In this work, the effect of MBE process control variables on the growth rate of the MgO film measured in nanometers per minute is investigated. Experiments are conducted at various process conditions and the resulting MgO film growth rate at each combination of process conditions is measured. The process control variables studied are the substrate temperature (100 °C – 300 °C), magnesium source temperature (328 °C – 350 °C), plasma intensity (0 mV – 550 mV), and percentage oxygen on the starting surface of 6H-SiC substrate (9 % – 13 %) after the substrate is prepared by high-temperature hydrogen etching. The film thickness is computed using the effective attenuation length (EAL) of silicon photoelectron peak intensity as measured by x-ray photoelectron spectroscopy (XPS). The film thickness is converted to growth rate by dividing it with the duration of film growth. Using the experimental data, a neural network model is developed to estimate growth rate for any given process variable combination. From this neural network model, multiple replications of data were generated to conduct a 3-level full factorial design of experiments and response surface-based analysis. The study reveals that the plasma intensity has the most significant influence on growth rate. The results indicate that growth rate is relatively low on high-quality substrates with √3 × √3 R30° reconstructed 6H-SiC (0001) surface with optimum oxygen content (approximately 10 %); in contrast, the growth rate is relatively high on substrates with high surface roughness and excessive oxygen on the starting substrate surface.

Properties of power electronic substrates based on thick printed copper technology

The aim of this work is to develop new metallisation procedures of 96% alumina substrates with copper using thick film technology and firing in a special batch furnace, designed for the process. Standard firing process of copper pastes is done in conveyor furnaces and it has been described in literature. The firing process in batch furnaces is characterised by different problems and it has not yet been published. The developed batch furnace can combine firing in a protective atmosphere e.g. that of high nitrogen purity gas, automated mixing of different gases, and evacuation of the furnace chamber using rotary pump. The work is concentrated on Heraeus pastes that make it possible to reach up to about 300μm film thickness and, if needed, high resolution pattern of lower film thickness on the same substrate, metallised through holes and application of ENIG metallisation. Principles and characteristics of particular firing phases in the batch furnace as well as morphology and film properties of the fired copper films are described in the paper. The whole metallisation process proved to be effective offering high quality substrates for power electronics at reasonable investment and production costs.

Understanding the distribution of wood-inhabiting fungi in European beech reserves from species-specific habitat models

Abstract We assessed how environmental drivers influence the occurrences of wood-inhabiting macrofungi in European beech forests, using an extensive dataset of fruit body records collected in 53 reserves across twelve European countries. We found that the 105 species included in this study varied greatly in their responses to covariates related to resource quality, climate and forest connectivity, both in the strength and direction of the observed effects. Climate was the most important driver for some species, while others responded more to connectivity, or simply to the presence of high quality substrates within the reserves. Species occurrences varied also across geographical regions, especially between the UK and the rest of Europe. Our results show that wood-inhabiting fungi in European beech forests respond individualistically to habitat filters and differ in their biogeographical distribution patterns, and they thus provide a detailed perspective of how wood-inhabiting fungal communities are structured across Europe.

Surface enhanced Raman scattering substrate with high-density hotspots fabricated by depositing Ag film on TiO2-catalyzed Ag nanoparticles

Surface enhanced Raman scattering (SERS) has been developed as a powerful tool for detection of ultra-trace molecules, thus at foundation of a number of important technologies, such as chemical analysis and biosensor. Photocatalytic growth of Ag nanoparticles (NPs) by TiO2 film is a cost-effective, facile and surfactantless way to fabricate SERS substrates with high stability and reproducibility, but the SERS activity still needs to be improved. In this work, we report a facile way to improve SERS activity of TiO2-catalyzed Ag NPs by additionally depositing a layer of Ag film using magnetron sputtering. Combining with the advantages of liquid and vapor environment, the Ag NPs size increase to the resonance size without decrease of density, so the spacing of Ag NPs decrease and high-density hotspots can be formed. By optimizing the sputtering time of Ag films, the SERS activity of the Ag NPs/films is improved by a factor of ∼400. This work not only establish a low-cost method for fabricating high-quality SERS substrate, more importantly, propose a novel way to prepare plasmonic nanostructures with high-density hotspots.

Optically Thin Metallic Films for High-Radiative-Efficiency Plasmonics.

Plasmonics enables deep-subwavelength concentration of light and has become important for fundamental studies as well as real-life applications. Two major existing platforms of plasmonics are metallic nanoparticles and metallic films. Metallic nanoparticles allow efficient coupling to far field radiation, yet their synthesis typically leads to poor material quality. Metallic films offer substantially higher quality materials, but their coupling to radiation is typically jeopardized due to the large momentum mismatch with free space. Here, we propose and theoretically investigate optically thin metallic films as an ideal platform for high-radiative-efficiency plasmonics. For far-field scattering, adding a thin high-quality metallic substrate enables a higher quality factor while maintaining the localization and tunability that the nanoparticle provides. For near-field spontaneous emission, a thin metallic substrate, of high quality or not, greatly improves the field overlap between the emitter environment and propagating surface plasmons, enabling high-Purcell (total enhancement >10(4)), high-quantum-yield (>50%) spontaneous emission, even as the gap size vanishes (3-5 nm). The enhancement has almost spatially independent efficiency and does not suffer from quenching effects that commonly exist in previous structures.

Nanometer-Thick Gold on Silicon as a Proxy for Single-Crystal Gold for the Electrodeposition of Epitaxial Cuprous Oxide Thin Films.

Single-crystal Au is an excellent substrate for electrochemical epitaxial growth due to its chemical inertness, but the high cost of bulk Au single crystals prohibits their use in practical applications. Here, we show that ultrathin epitaxial films of Au electrodeposited onto Si(111), Si(100), and Si(110) wafers can serve as an inexpensive proxy for bulk single-crystal Au for the deposition of epitaxial films of cuprous oxide (Cu2O). The Au films range in thickness from 7.7 nm for a film deposited for 5 min to 28.3 nm for a film deposited for 30 min. The film thicknesses are measured by low-angle X-ray reflectivity and X-ray Laue oscillations. High-resolution TEM shows that there is not an interfacial SiOx layer between the Si and Au. The Au films deposited on the Si(111) substrates are smoother and have lower mosaic spread than those deposited onto Si(100) and Si(110). The mosaic spread of the Au(111) layer on Si(111) is only 0.15° for a 28.3 nm thick film. Au films deposited onto degenerate Si(111) exhibit ohmic behavior, whereas Au films deposited onto n-type Si(111) with a resistivity of 1.15 Ω·cm are rectifying with a barrier height of 0.85 eV. The Au and the Cu2O follow the out-of-plane and in-plane orientations of the Si substrates, as determined by X-ray pole figures. The Au and Cu2O films deposited on Si(100) and Si(110) are both twinned. The films grown on Si(100) have twins with a [221] orientation, and the films grown on Si(110) have twins with a [411] orientation. An interface model is proposed for all Si orientations, in which the -24.9% mismatch for the Au/Si system is reduced to only +0.13% by a coincident site lattice in which 4 unit meshes of Au coincide with 3 unit meshes of Si. Although this study only considers the deposition of epitaxial Cu2O films on electrodeposited Au/Si, the thin Au films should serve as high-quality substrates for the deposition of a wide variety of epitaxial materials.

Formation and Reduction of Large Growth Pits on 100 mm 4° 4H-SiC

The large growth pits (LGPs) dependence of substrate quality, growth rate, and C/Si ratio have been discussed in the 4H-SiC epitaxial growth on 100 mm N-type 4H-SiC Si-face substrates misoriented by 4° toward [11-20] with a warm-wall planetary reactor. The formation and reduction of LGPs have been investigated by adjusting the growth process parameters. With the optimized process, the perfect surface morphology with lower LGPs density has been obtained on the high quality substrate.

The effect of sewage sludge biochar on peat-based growing media

Peat is the main component of growing media in horticulture. Increasing demand, environmental concerns and rising costs for peat make the search for alternative materials imperative. Much research has been performed aiming to find high quality and low cost substrates from different organic wastes such as compost and thus decrease peat consumption. Biochar is a carbon-rich material that has attracted important research as a soil amendment. However, its potential utilization as a peat substitute for growing media formulation remains less well explored. The aim of this study was to evaluate the effects of sewage sludge and sewage sludge biochar on peat properties as growing media and on lettuce (Lactuca sativa) growth. Sewage sludge transformation into biochar proved to be a sustainable waste management approach in order to promote their future use as growing media components. Addition of biochar from sewage sludge increased the N, P and K content of growing media. The biochar addition to peat at a 10%vol rate increased lettuce biomass production by 184–270% and the shoot length by 137–147% despite hydrophysical properties not being improved. Also, biochar addition had a positive effect on growing media microbial biomass which increased more than 966%. In spite of the higher metal concentration in biochar than in sewage sludge, their transfer to plants seems to be reduced when compared with direct sewage sludge use.

Fabrication of high-quality GaN substrates using the Na flux method

Gallium nitride (GaN) substrates fabricated along the nonpolar and semipolar directions are the most promising materials for realizing optical and electronic devices with low power consumption. In this study, we carry out the Na flux growth on -plane GaN templates grown heteroepitaxially on sapphires. The GaN crystals are grown at low supersaturation using the Na flux method with the dipping technique. The crystallinity of the grown GaN crystals is improved compared to that of the seed substrates. Then it improves further by lowering the supersaturation. Finally, we succeed in fabricating a 2-in. -plane GaN single crystal with high transparency and crystallinity.

Analyses of single crystal diamond substrates grown in a pocket substrate holder via MPACVD

High quality single crystal diamond (SCD) substrates are required for several different important current applications. Microwave Plasma Assisted Chemical Vapor Deposition (MPACVD) is a convenient deposition method for high quality substrates. It is hence imperative to synthesize and analyze substrates grown via different CVD techniques. This paper describes the quality of single crystal diamond substrates which have been grown via one such deposition strategy, which is in a “pocket substrate holder” design. The growth process in such a holder helps in depositing substrates which have almost no polycrystalline diamond (PCD) rim growth. The exact pocket holder growth process at high pressures (240 Torr) and high microwave power densities (~ 500 W/cm3) has been discussed in a previous publication [1]. The SCD CVD substrates were analyzed with different characterization techniques. By synthesizing diamond substrates in a pocket holder, the lack of any/almost any PCD rim helped in reducing the amount of stress in the crystals. To study the electronic quality of the substrates, etching experiments were conducted to determine the etch pit density. Nomarski images confirm that the number of etch pits at the edges is higher than at the center of the etched surface thereby implying the feasibility of this simpler method of reducing the etch pit density. The pocket holder process thus not only reduces the PCD rim but also reduces the substrate etch pit density and hence shows good promise of delivering high quality substrates.

High-quality, 2-inch-diameter m-plane GaN substrates grown by hydride vapor phase epitaxy on acidic ammonothermal seeds

In this paper, we discusse the origin of basal-plane stacking faults (BSFs) generated in the homoepitaxial hydride vapor phase epitaxy (HVPE) growth of m-plane gallium nitride (GaN). We investigated the effects of seed quality, especially dislocation density, on BSF generation during homoepitaxy. The results clearly identify basal-plane dislocation in the seed as a cause of BSF generation. We realized high-quality m-plane GaN substrates with a 2-in. diameter using HVPE on low-dislocation-density m-plane seeds.

Fabrication of freestanding heteroepitaxial diamond substrate via micropatterns and microneedles

The fabrication of a high-quality freestanding diamond substrate was successfully demonstrated via heteroepitaxy by introducing diamond micropatterns and microneedles in the early stage of growth. Micropatterns contributed to a marked reduction in the number of dislocations induced by epitaxial lateral overgrowth, and microneedles relaxed heteroepitaxial strain. Raman spectroscopy indicated the absence of nondiamond carbon inclusions in the obtained freestanding substrate. The full width at half maximum of the X-ray rocking curve for diamond (004) reflections was 0.07°, the lowest value for heteroepitaxial diamond that has been reported so far. The results provide novel insights toward realizing large-diameter single-crystalline diamond substrates.

Epitaxial Atomic Layer Deposition of Sn-Doped Indium Oxide

Coherently strained, epitaxial Sn-doped In2O3 (ITO) thin films were fabricated at temperatures as low as 250 °C using atomic layer deposition (ALD) on (001)-, (011)-, and (111)-oriented single-crystal Y-stabilized ZrO2 (YSZ) substrates. Resultant films possess cube-on-cube epitaxial relationships with the underlying YSZ substrates and are smooth, highly conductive, and optically transparent. This epitaxial ALD approach is favorable compared to many conventional growth techniques as it is a large-scale synthesis method that does not necessitate the use of high temperatures or ultrahigh vacuum. These films may prove valuable as a conductive growth template in areas where high-quality crystalline thin film substrates are important, such as solar energy materials, light-emitting diodes, or wide bandgap semiconductors. Furthermore, we discuss the applicability of this ALD system as an excellent model system for the study of ALD surface chemistry, nucleation, and film growth.

The effect of pruning waste and biochar addition on brown peat based growing media properties

Peat is a crucial carbon sink in the terrestrial ecosystem, but it is jeopardized by its use as fuel or as growing media. In the last years, much research has been performed aiming to find high quality and low cost substrates from different organic wastes in order to decrease peat consumption. Biochar is a carbon-rich material that has attracted important research as soil amendment. However, its potential utilization as peat substitute for growing media formulation remains less well explored. The main objective of this work was to study the effect on peat based growing media of pruning waste (PW) and three biochars: a commercial charcoal (CC), biochar from slow pyrolysis of PW at 300°C (B300) and 500°C (B500) added at different ratios. The chemical properties of some mixtures were adequate as growing media materials. Hydrophysical properties of peat changed with biochar and pruning waste additions. B500 and CC additions (in 50 and 75vol%) increased air space volume. All mixtures showed lower water holding capacities than peat and only mixtures with B500 lead to adequate holding capacity and porosity values for substrate materials. Finally, lettuce (Lactuca sativa) was grown in the different substrates and, after 5 weeks, the results have shown that lettuce biomass was substantially higher with peat plus biochar samples obtained from pyrolysis of pruning waste at 300 and especially 500°C than with peat alone. Our results imply that pruning residue biochar can be an improved growing media as peat substitute for soilless vegetable production.

Synthesis and optical characterization of a high-quality ZnS substrate for optoelectronics and UV solar-energy conversion

A high-grade cubic ZnS substrate crystal with longer range order and a strong band-edge emission was clearly demonstrated.