Si Substrates Research Articles

Terahertz and Infrared Plasmon Polaritons in PtTe2 Type-II Dirac Topological Semimetal.

Surface plasmon polaritons (SPPs) are electromagnetic excitations existing at the interface between a metal and a dielectric. SPPs provide a promising path in nanophotonic devicesforlight manipulation at the micro and nanoscale with applications in optoelectronics, biomedicine, and energy harvesting. Recently, SPPs have been extended to unconventional materials like graphene, transparent oxides, superconductors, and topological systems characterized by linearly dispersive electronic bands. In this case, three-dimensional Dirac and Weyl semimetals offer a promising frontier for infrared (IR) and terahertz (THz) radiation tuning by topologically-protected SPPs.In this work, we investigate the THz-IR optical response, of platinum ditelluride (PtTe2) type-II Dirac topological semimetal films grown on Si substrates. We detect SPPs generated on microscale ribbon arrays of PtTe2in the far-field limit,finding an excellent agreement among measurements, theoretical model, and electromagnetic simulation data.The far-field measurements have been further supported by near-field infrared data which indicate a strong electric field enhancement due to the SPP excitation near the ribbon edges. The whole results of this paper, indicate that PtTe2ribbon array appears an idealactive layout for geometrically tunable SPPs thus inspiring a new fashion of optically tunable materials in the technologically demanding THz and IR spectrum. This article is protected by copyright. All rights reserved.

V2O5 nanoflakes for broad-spectral-response self-powered photodetectors with a high on/off ratio and high detectivity

In this study, V2O5 nanoflakes (NFs) was coated on Si substrate by DC sputtering to obtain V2O5 NFs/n-Si heterojunction. To utilize V2O5 NFs as a broadband photodetector, absorbance spectra were studied using UV−Vis−near-IR spectroscopy. Cut-off wavelength was 530 nm. Furthermore, energy dispersive x-ray, x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS) and scanning electron microscope analyses of V2O5 NFs were achieved. The V2O5 NFs/n-Si device gave a very high rectifying ratio of 1.18 × 104 in the dark and at zero bias, it has self-powered mode and an on/off ratio of 1.29 × 106. Optical analyses of the V2O5 NFs/n-Si heterojunction device were studied in detail under UV (365, 395 nm) and IR (850 nm) illumination as well as visible light with varying light intensities. Analysis of experimental studies showed that the device has a high photoresponse under all illuminations. For optical analysis based on I–V measurements, responsivity, detectivity, on/off ratio, external quantum efficiency (EQE), normalized photocurrent-dark-current ratio and noise-equivalent power (NEP) analyses were achieved. The maximum values of responsivity from measurements under visible, UV (395 nm) and IR illumination (850 nm) were 104, 882 and 850 mA W−1 for −2.0 V, respectively. Detectivity values are maximized at V = 0 V and are 6.84 × 1011, 7.87 × 1012 and 6.87 × 1012Jones for the same illuminations respectively. With increasing intensity, the rectification ratio and NEP decreased while the other parameters generally increased. The increase in performance at increasing visible intensity was attributed to the increase in photogenerated carrier density at high intensities, and the high performance in the UV region was attributed to the high light absorption of V2O5 NFs in the UV region.

Low-cost O2 plasma activation assisted direct bonding of β-Ga2O3 and Si substrates in air

This study presents a novel technique for directly bonding β-Ga2O3 and Si substrates using O2 plasma activation at room temperature. The activation process resulted in excellent surface hydrophilicity and roughness. Annealing in an N2 atmosphere revealed a bonding strength of 6.23 MPa, with partial fracture of the Si substrate. The bonding interface was observed by TEM and EDS. A distorted amorphous intermediate layer with a thickness of 100 nm and amorphous bubbles were observed in the bonding interface. In addition, the Ga, O, and Si elements were diffused and enriched, forming approximately 30 nm nodules at the bonding interface. This method offers a promising approach for integrating wide bandgap semiconductor materials in devices, bypassing the need for vacuum treatment.

Elucidating the formation mechanisms of the parasitic channel with buffer-free GaN/Si hetero-bonding structures

Driven by the increasing demand for 5G communication, GaN radio frequency (RF) device on Si technology has been flourishing attributable to the large size, low cost, and compatibility with complementary metal–oxide–semiconductor technology. However, a significant challenge is that a high-conductance parasitic channel forms at the interface between the III-N epitaxial layers and the Si substrate, leading to severe RF loss, which has been considerably impairing both the performance and advancement of RF GaN-on-Si technologies. Despite continuing controversies concerning the physical mechanisms engendering the parasitic channel, clarification is critically needed. Standing apart from traditional studies on RF loss in III-N epilayers grown on Si, this article comprehensively investigates the bonding interface of GaN thin film and Si(100) substrate realized via direct surface activated bonding and ion-cutting technologies. It was clearly determined that substantial diffusion of gallium (Ga) atoms into the Si substrate at the bonding interface occurred even at an annealing temperature as low as 350 °C. Subsequent high-temperature post-annealing at 800 °C intensified this diffusion, activating Ga atoms to form a p-type highly conductive parasitic channel. Simultaneously, it triggered Ga atoms aggregation and incited melt-back etching within the Si substrate at the interface. Contrasting with the conventional hetero-epitaxy, this study presents a compelling view based on the bonding technique. It conclusively elucidates the physical mechanisms of the formation of the primary source of RF loss—the p-type highly conductive parasitic channel.

Band gap tunability in DC sputtered Ni-doped ZnO thin films for wide usage in optoelectronic gadgets

ZnO thin films have brought significant applicability in optoelectronic and energy storage devices based on their environmental friendliness. Pristine ZnO, 6.25 % and 12.5 % Ni-doped ZnO thin films were deposited on Si substrate via direct current and radio frequency magnetrons, respectively. The X-ray diffraction patterns exhibited phase purity of synthesized thin films. The micrographs showed reduction in average grain size for pure ZnO, 6.25 % and 12.5 % Ni-doped ZnO as 95 nm, 70 nm and 60 nm, respectively. The elemental purity was confirmed by energy dispersive X-ray. The ellipsometric analysis showed that Ni inclusion brought band gap variation from 3.06 to 3.08 eV for pure ZnO to 12.5 % Ni-doped ZnO thin films. The real part of dielectric constant enhanced from 3.60 to 3.75 for 12.5 % Ni-doped ZnO, simultaneously depicting reduction in dielectric loss from 0.45 to 0.40. Conclusively, proposing Ni-doped ZnO thin films with low dielectric loss as a potential candidate in optoelectronic industry.

Highly crystalline yttria‐stabilized zirconia and titania thin films on plastic substrates via sol‐gel transfer process

AbstractWe prepared yttria‐stabilized zirconia (YSZ) and titania crystalline thin films on polycarbonate (PC) substrates by the sol‐gel transfer technique that we have developed recently. Precursor gel films were deposited by spin‐coating on a polyimide/polyvinylpyrrolidone mixture layer on Si(100) substrates, and then were calcined at 600°C. The spin‐coating and the calcination were cycled, followed by final firing at 600–1000°C, to obtain 140–190 nm thick, YSZ and titania crystalline thin films. The film densification progressed as the final firing temperature increased, where the porosity calculated from the refractive index decreased down to a few percent. The film thus obtained was heated at 190°C on a hot plate, and a PC substrate was pressed on the film to transfer it to the PC substrate. The transferability quantified by image analysis of the film area was found to be significantly different between the YSZ and titania films. In the case of YSZ films, the area of silicon that was fractured and adhered to the transferred film increased significantly with increasing firing temperature, leading to a decrease down to 0% in the fraction of the successful transfer area without such a damage. On the other hand, the fraction of the successful transfer area remained around 90% irrespective of the firing temperature for the titania films. The surface of the titania films that were fired at 800–1000°C and transferred to PC substrates had voids of several tens nm scale, which may have been formed during anatase‐to‐rutile phase transformation. We thought that the reduced titania/Si(100) contact area due to such void formation facilitated the delamination of the titania films from Si(100) substrates. High temperature firing, which promotes crystallization and densification of films, thus affects differently the film transferability to plastic substrates, depending on the type of films. The work also suggested possible use of titania films as release‐assisting layers.

Cu thin film growth on stepped Si substrate: Effects of incident energy and thermal annealing

The existence of defects on the substrate surface is unavoidable and has a significant impact on the determination of surface properties. Among the prevalent types of defects, steps play an important role. In this study, molecular dynamics simulations are employed to explore the growth process of a thin film of Cu on a Si (001) substrate with a step. This research investigates how incident energy and thermal annealing affect the growth mode, surface roughness, film-substrate interface, and dislocation evolution. The results indicate that during the initial stage of the growth, the nucleation phenomenon was observed on terraces. The simulation indicates that the Cu atoms occur in an island growth mode on the stepped substrate. It is found that when the incident energy is increased and thermal annealing is performed, the surface curvature and roughness are reduced. Furthermore, the intermixing thickness at the interface increases due to the variation of the incidence energy. A dislocation analysis revealed that some dislocations disappeared before and after annealing, and a perfect dislocation appeared by increasing the incident energy.

Effect of annealing temperature on crystallographic texture, magnetic and microwave properties of barium ferrite thin films

Abstract Due to it has large saturation magnetization (Ms), high magnetocrystalline anisotropy field and high ferromagnetic resonance (FMR) frequency. Barium ferrite (BaM) has attracted more and more attentions in the fields of magnetic recording media, permanent magnets and microwave devices. Here, BaM thin films were deposited on Pt-coated Si substrate, and the effect of annealing temperature on the microstructure and magnetic and microwave properties of barium ferrite thin films in detail. It is found that when the BaM thin film was annealed at 1035°C, it has good properties. The XRD data provide clear evidence that the BaM thin films have high c-axis orientation, and the Lotgering factor is as high as 0.96. The AFM morphology show that BaM grains are out of the film plane, and there are hexagonal. The magnetic hysteresis curves indicated that Both saturated magnetization (4πMs), remanence ratio and OP coercive (Hc) increase with increasing Ta, and get the maximum value at 1035 °C. The ferromagnetic resonance (FMR) measurement show that the FMR linewidth is 143 Oe@50 GHz, it means that this this sample has low microwave loss in millimeter wave loss. These results make sure that this BaM thin film is possible use in millimeter wave devices such as filers, circulators and isolators. 

Effective Carrier Lifetime in Ultrashort Pulse Laser Hyperdoped Silicon: Sulfur Concentration Dependence and Practical Limitations

Charge carrier lifetime is a crucial material parameter in optoelectronic devices and knowing the dominant recombination channels points the way for improvements. The effective carrier lifetime τeff of surface‐passivated hyperdoped (hSi) and nonhyperdoped “black” (bSi) silicon by quasi‐steady‐state photoconductance decay (QSSPC) measurements and its evolution upon controlled wet‐chemical etching are studied. Sample preparation involves the irradiation of Si by numerous ultrashort laser pulses either in SF6 for hSi or ambient atmosphere for bSi. Findings suggest that the hSi is composed of a double layer: 1) an amorphous resolidified top layer with about 92% of the total incorporated sulfur that accounts for the sub‐bandgap absorptance and 2) a crystalline layer underneath in which sulfur concentration tails off toward the Si substrate. The effective lifetime is deconstructed by a 1D simulation to quantify the impact of the local lifetime of the defect‐rich top layer, τtop. It is found that by the QSSPC method, a maximum τtop for 1) can be estimated. For 2), τtop between 2 and 8 ns is estimated. The bSi sample shows a faster lifetime recovery upon etching which suggests that in hSi samples purely laser‐induced defects are not limiting the carrier lifetime compared to sulfur‐related defects.

Enhancement of ferroelectricity in chemical-solution-deposited ZrO2 thin films through fine phase transition control

Recent studies have highlighted the ferroelectric potential of ZrO2 thin films, which offer advantages over HfO2-based ferroelectric materials, such as lower thermal budget and greater natural abundance. In this research, pure ZrO2 ferroelectric thin films were fabricated on Si substrates using chemical solution deposition with all-inorganic precursors. We explored the impacts of film thickness and HfO2 seed layers on phase transition and ferroelectric properties. Notably, an 11 nm thick ZrO2 film exhibited ferroelectric behavior with a remanent polarization of 12.6 μC/cm2. Due to the combined effects of tensile stress and surface energy, the increase in thickness to 30 nm led to a phase transition from the orthorhombic phase to the monoclinic phase and a resultant decrease in remanent polarization. Additionally, the introduction of an HfO2 seed layer facilitated the crystallization of the ferroelectric o-phase, enhancing the remanent polarization to 16.5 μC/cm2 in our ∼8 nm thick ZrO2 thin film with a ∼2 nm thick HfO2 seed layer. These findings provide valuable insights into optimizing ferroelectric properties in ZrO2 thin films through phase transition control.

Synthesis of Wrinkled MoS2 Thin Films Using a Two-Step Method Consisting of Magnetron Sputtering and Sulfurization in a Confined Space

Synthesis of Wrinkled MoS2 Thin Films Using a Two-Step Method Consisting of Magnetron Sputtering and Sulfurization in a Confined Space

Epitaxial growth of Ca(Ge1−xSnx)2 with group IV 2D layers on Si substrate

Two-dimensional (2D) material is drawing considerable attention as a promising thermoelectric material. This study establishes the formation method of renewed Ca-intercalated group IV 2D materials, Ca(Ge1−x Sn x )2 crystals including germanene-based 2D layers. The solid phase epitaxy allows us to form epitaxial Ca(Ge1−x Sn x )2 on Si. Atomic force microscopy reveals that the Ca(Ge1−x Sn x )2 has island structures. X-ray diffraction proved the epitaxial growth of the Ca(Ge1−x Sn x )2 island structures and the increase of the c-axis lattice constant with Sn content increase. The formation of this renewed intermetallic compound including group IV 2D layer opens an avenue for high performance thermoelectric generator/Si.

Effect of Si concentration and substrate temperature on the microstructure and magnetic properties of FeCoNiCu0.5Six high entropy alloy films

It has been known that Si has the effect to increase the resistivity, permeability, and to decrease the magnetostriction coefficient in Si-containing steel as soft magnetic material. On the other hand, high-entropy alloys are intensively studied as soft magnetic materials in recent years, especially as thin films. In the present work, Si-containing (FeCoNiCu0.5Six) high entropy alloy films (HEAFs) have been prepared by magnetron co-sputtering under different deposition conditions. The microstructure and magnetic properties of FeCoNiCu0.5Six HEAFs have been investigated to clarify the effects of Si concentration on microstructure formation and magnetic properties. It has been found that Si addition strongly affects the magnetic properties of FeCoNiCu0.5Six HEAFs of FCC phase by decreasing the coercivity of the films, but hardly affects the phase formation in the films. On the other hand, it has been found that deposition of the films at moderate high substrate temperatures greatly improve the magnetic properties by increasing the saturation magnetization while keeping low coercivity.

Investigation of electronic, ferroelectric and local electrical conduction behavior of RF sputtered BiFeO3 thin films

Most of the applied research on BiFeO3 (BFO) focuses on magnetoelectric and spintronic applications. This calls for a detailed grasp of multiferroic and conduction properties. BFO thin films with (100) epitaxial growth has been deposited on a LaNiO3 (LNO) buffered Pt/Ti/SiO2/Si(100) substrate using RF magnetron sputtering. The film formed at 15 mTorr, 570 °C, and with Ar/O2 4:1 had a reasonably high degree of (100)-preferential orientation, the least surface roughness, and a densely packed structure. We obtained ferroelectric loops with strong polarization (150 μC cm−2). The leakage current density is as low as 10–2 A cm−2 at 100 kV cm−1, implying that space-charge-limited bulk conduction (SCLC) was the primary conduction channel for carriers within BFO films. Local electrical conduction behavior demonstrates that at lower voltages, the grain boundary dominates electrical conduction and is linked to the displacement of oxygen vacancies in the grain boundary under external electric fields. We hope that a deeper understanding of the conduction mechanism will help integrate BFO into viable technologies.

Fabrication of penetrating pores in epitaxial Ge-on-Si through preferential etching along threading dislocations

Epitaxial Ge-on-Si possesses a high density of threading dislocations (TDs) due to the lattice mismatch and difference in thermal expansion coefficient. By employing the lattice distortion at the TDs, we demonstrate that penetrating pores along TDs can be formed in both p- and n-type heteroepitaxial Ge layers through a preferential etching. It has been found that the preferential etching at TD sites takes place in the porosification process of Ge-on-Si samples and is independent of the doping type and concentration. The penetrating pores follow the path of the TD lines and can penetrate the entire Ge layer of 1.3 μm to further porosificate the Si substrate. The effects of anodic current density and total etching duration have been thoroughly investigated on forming penetrating pores at TD sites. The dissolution mechanism in the porosification process has been revealed by dissolution valence calculation and recorded potential curves. Our findings shed light on Ge perforation in both p- and n-type Ge-on-Si and show great potential in Si-based integrated photonics and microelectronics.

Ultrathin and Deformable Graphene Etch Mask for Fabrication of 3D Microstructures.

Three-dimensional (3D) microfabrication techniques play a crucial role across various research fields. These techniques enable the creation of functional 3D structures on the microscale, unlocking possibilities for diverse applications. However, conventional fabrication methods have limits in producing complex 3D structures, which require numerous fabrication steps that increase the costs. Graphene is an atomically thin material known for its deformability and impermeability to small gases and molecules, including reactive gases like XeF2. These features make graphene a potential candidate as an etch mask for 3D microfabrication. Here, we report the fabrication of various 3D microstructures using graphene etch masks directly grown and patterned on a Si substrate. The patterned graphene deforms and wraps the etched structures, allowing for the fabrication of complicated 3D microstructures, such as mushroom-like and step-like microstructures. As a practical demonstration of the graphene etch mask, we fabricate an omniphobic surface of reentrant 3D structures on a Si substrate. Our work provides a method for fabricating complex 3D microstructures using a graphene etch mask, contributing to advancements in etching and fabrication processes.

Actively tunable laser action in GeSn nanomechanical oscillators.

Mechanical forces induced by high-speed oscillations provide an elegant way to dynamically alter the fundamental properties of materials such as refractive index, absorption coefficient and gain dynamics. Although the precise control of mechanical oscillation has been well developed in the past decades, the notion of dynamic mechanical forces has not been harnessed for developing tunable lasers. Here we demonstrate actively tunable mid-infrared laser action in group-IV nanomechanical oscillators with a compact form factor. A suspended GeSn cantilever nanobeam on a Si substrate is resonantly driven by radio-frequency waves. Electrically controlled mechanical oscillation induces elastic strain that periodically varies with time in the GeSn nanobeam, enabling actively tunable lasing emission at >2 μm wavelengths. By utilizing mechanical resonances in the radio frequency as a driving mechanism, this work presents wide-range mid-infrared tunable lasers with ultralow tuning power consumption.

Fabrication of magnetic field sensor based on a Co-based Schottky heterojunction

We have prepared a reliable magnetic field sensor based on a Co-based Schottky heterojunction with the possibility of finding practical application when the current–voltage (I–V) characteristics of the heterojunctions were modified by the external magnetic fields. For this purpose, the heterojunctions based on ferromagnetic thin films Co were deposited on Si (100) substrate via ultra-thin Pt films. The structural and magnetic properties of the heterojunctions were demonstrated, the crystal structure and the saturation magnetization of heterojunctions significantly increased with the increase of annealing temperatures. The electrical properties of the Co/Pt/Si heterojunction were investigated using temperature-dependent I–V characteristics, the rectifying properties were observed in the whole temperature ranging from 233 K to 283 K. Based on a simplified energy band structure, the magnetic field transport properties of Co/Pt/Si heterojunctions were investigated by taking into account the effects of spin and magnetic field on the potential barrier height of Co/Pt/Si heterojunctions. The results showed that the experimental ratio of current measured in a magnetic field B and in zero magnetic field (I(B)/I(0)) is linearly with the magnetic field B and almost independent of the applied voltage. The sensitivity and linearity of the magnetic field sensor were measured. The sensitivity of the sensor can reach 72.09 μA/T at an applied voltage frequency of 2000 Hz, which indicates that the linearity and sensitivity of the sensor are improved with the increase of the applied voltage frequency. The proposed sensors would be easy to integrate with current semiconductor processes with simple structure and they could be suitable for geological applications such as energy exploration.

Epitaxial twin coupled microstructure in GeSn films prepared by remote plasma enhanced chemical vapor deposition

Growth of GeSn films directly on Si substrates is desirable for integrated photonics applications since the absence of an intervening buffer layer simplifies device fabrication. Here, we analyze the microstructure of two GeSn films grown directly on (001) Si by remote plasma-enhanced chemical vapor deposition (RPECVD): a 1000 nm thick film containing 3% Sn and a 600 nm thick, 10% Sn film. Both samples consist of an epitaxial layer with nano twins below a composite layer containing nanocrystalline and amorphous. The epilayer has uniform composition, while the nanocrystalline material has higher levels of Sn than the surrounding amorphous matrix. These two layers are separated by an interface with a distinct, hilly morphology. The transition between the two layers is facilitated by formation of densely populated (111)-coupled nano twins. The 10% Sn sample exhibits a significantly thinner epilayer than the one with 3% Sn. The in-plane lattice mismatch between GeSn and Si induces a quasi-periodic misfit dislocation network along the interface. Film growth initiates at the interface through formation of an atomic-scale interlayer with reduced Sn content, followed by the higher Sn content epitaxial layer. A corrugated surface containing a high density of twins with elevated levels of Sn at the peaks begins forming at a critical thickness. Subsequent epitaxial breakdown at the peaks produces a composite containing high levels of Sn nanocrystalline embedded in lower level of Sn amorphous. The observed microstructure and film evolution provide valuable insight into the growth mechanism that can be used to tune the RPECVD process for improved film quality.

Resilient Si@C architecture fabricated by mechanochemical conjugation and thermal reduction for lithium storage: Simulation on interfacial state evolution

Synchronal comminution via high-energy bead milling not only efficiently pulverizes Si particles and exfoliates graphene oxide (GO) sheets but also facilitates Si surface functionalization and intensify Si-C conjugation. After a thermal reduction, a well-wrapped Si@C anode material can be fabricated for lithium storage. The discharge specific capacities of this Si@C composite sustain at 1110.3 mAh g−1 after 300 cycles at 1 A g−1 and 316.4 mAh g−1 for 800 cycles at 5 A g−1, which are respectively 1.35 and 2.07 times that of its random blended Si/C counterpart. By employing molecular dynamics (MD) simulations with ReaxFF reactive force field to investigate the mechanochemical reactions between Si and GO amidst high-energy milling, an atomic scale portrayal of Si crystal fragmentation and Si-C bonding can be depicted. Analyses focusing on the differential forces exerted on various Si crystal planes, coupled with potential energy (PE) trends, reveal a higher propensity for cleavage in (111) plane, with (311) plane followed. Radial distribution function (RDF) outcomes indicate that ball milling leads to substantial disruption of crystalline order in Si particles, generating a plethora of Si dangling bonds. This disruption stimulates the formation of SiOOC, SiOC and SiC bonds at the Si/C interface, thus enhancing the integration of GO with Si substrate. Subsequent thermal reduction processes not only restore the structural order of Si and GO but also consolidate Si/C bonding.