Si Substrates Research Articles

Incorporation of carbon quantum-dot films with silicon substrates for improved photovoltaic performances

Employment of fluorine-ion doped carbon quantum dot (FCQD) films with silicon (Si) substrates is realized via the facile solution process that exhibits the remarkable photovoltaic characterizations. In-depth materials and cell characterizations are performed, and the improvement of charge separation at FCQD/Si interfaces compared with undoped CQD/Si cases are experimentally elucidated, showing the conversion efficiency of 13.6 %, approximately 2 times higher than undoped CQD-based solar cells with conversion efficiency of 6.8%. The results are of great importance for QD-based light-harvesting and optoelectronic applications.

A newly developed Cu(Rh) alloy film and its characteristics and applications

A new type of copper (Cu)-rhodium (Rh)-alloy, Cu(Rh), films is developed by co-sputtering copper and rhodium onto silicon (Si) substrates under an argon (Ar) atmosphere. The new films are next annealed at 600 and 670 °C, or alternatively at 100 and 450 °C, for 1 h. Longer annealing to the films, for up to 8 days, is also conducted to explore resistivity variation. The resistivity of the new 300-nm-thick film is 2.19 μΩ cm after annealing at 670 °C for 1 h and drifts to 2.26 and 2.14 μΩ after annealing at 400 and 450 °C, respectively, for 200 h. A 2.7-μm-thick Sn layer is then thermally evaporated atop the new film for stable flip-chip solder joints; their metal and Cu-Sn intermetallic compound (IMC) growth processes vs. various annealing periods are tested. After annealing at 670 °C, the new 300-nm-thick film’s adhesive strength reaches 44.2 ± 0.01 MPa, which is 11 ~ 12-fold that of their pure Cu counterpart. Some key test results of the new film are disclosed herein, including its X-ray diffraction (XRD) patterns, transmission electron microscopy (TEM) images, secondary-ion mass spectrometry (SIMS), time-dependent dielectric-breakdown (TDDB) lifetime curves, and adhesive strength. The new film’s antibacterial efficacy arrives at an antibacterial ratio of approximately 100% against Staphylococcus aureus (S. aureus) BCRC 10451 for the 300-nm-thick film and approximately 99.82% for the 8 nm film, far superior to that of a pure Cu film, which is 0 with the same annealing temperature range. The new film, hence, seems to be a remarkable candidate material for various industrial applications, such as ultra-large-scale integrated circuits (ULSIC), micro-electronic circuits, printed circuits, flip-chip technology, medical care concerning antibacteria, and the like.Graphical A new type of copper (Cu)-rhodium (Rh)-alloy, Cu(Rh), films is developed by co-sputtering copper and rhodium onto silicon (Si) substrates under an argon (Ar) atmosphere and then annealing the new films at 600 and 670 °C, or alternatively at 100 and 450 °C, for 1 h. Longer annealing to the films, for up to 8 days, is also conducted to explore resistivity variation. The resistivity of the new 300-nm-thick film is 2.19 mW cm after annealing at 670°C for 1 h and drifts to 2.26 and 2.14 mW after annealing at 400 and 450 °C, respectively, for 200 h. A 2.7-μm-thick Sn layer is next thermally evaporated atop the new film for stable flip-chip solder joints; their metal and Cu-Sn intermetallic compound (IMC) growth processes vs. various annealing periods are tested. After annealing at 670°C, the new 300-nm-thick film’s adhesive strength reaches 44.2 ± 0.01 MPa, which is 11~12-fold that of their pure Cu counterpart. Some key test results of the new film are disclosed herein, including its X-ray diffraction (XRD) patterns, transmission electron microscopy (TEM) images, secondary-ion mass spectrometry (SIMS), time-dependent dielectric-breakdown (TDDB) lifetime curves, and adhesive strength. The new film’s antibacterial efficacy arrives at an antibacterial ratio of approximately 100% against Staphylococcus aureus (S. aureus) BCRC 10451 for the 300-nm-thick film and approximately 99.82% for the 8-nm film, far superior to that of a pure Cu film, which is 0 with the same annealing temperature range. The new film, hence, seems to be a remarkable candidate material for various industrial applications, such as ultra-large-scale integrated circuits (ULSIC), micro-electronic circuits, printed circuits, flip-chip technology, medical care concerning antibacteria, and the like.

Investigating the physical mechanism of ion-slicing in AlN and hetero-integrating AlN thin film on Si(100) substrate

Heterogeneously integrating the monocrystal AlN thin films on Si(100) substrates by ion-slicing technique provides a promising high-quality material platform to achieve the monolithic integration of Silicon-based CMOS (Complementary Metal Oxide Semiconductor) and high-performance III-nitride devices. Single crystalline AlN bulk materials implanted by hydrogen ions (H+) were used to elucidate the physical mechanism of the blistering formation in hydrogen implanted AlN with different annealing process. XTEM characterization was performed to reveal the formation of H-induced microcracks which eventually leads to the layer splitting. Using the ion-slicing technique, the AlN thin films were capitally transferred to Si(100) substrate. The crystal quality and the microstructure of the transferred AlN thin film were characterized thoroughly, indicating its exceptional crystal quality with the full width at half maximum (FWHM) for (002) XRC as low as 93.6 arcsec.

Multilevel Ferroelectric Domain Wall Memory for Neuromorphic Computing

AbstractLow‐power and parallel processing Neuromorphic computing that imitates on the human brain's extraordinary data processing and learning capabilities is promising in non‐von Neumann application platforms in the post‐Moore era. Ferroelectric domain walls appearing as nanoscale topological defects in solids exhibit coexisting ordering parameters besides the spontaneous polarization, leading to the emergence of rich physics and electronic effects in the development of neuromorphic electronics that go beyond the conventional CMOS. In this study, the four‐state domain wall memory is developed on LiNbO3 ferroelectric thin films integrated with Si substrates, where each state can be stably manipulated at a specific low voltage, showcasing outstanding fatigue resistance and retention performance. The constructed crossbar array that functions as a kernel for image convolution can be used to implement processing operations like image filtering, sharpness enhancement, and edge detection. Additional simulation from a convolutional neural network model shows 96.98% accuracy on the Modified National Institute of Standards and Technology handwritten digits dataset. The stable multi‐state domain wall memory provides a new approach for computing and promotes research in domain wall electronics to meet future enormous demands of big data.

Self-Powered Broadband Photodetector Based on NiO/Si Heterojunction Incorporating Graphene Transparent Conducting Layer.

In this study, a self-powered broadband photodetector based on graphene/NiO/n-Si was fabricated by the direct spin-coating of nanostructured NiO on the Si substrate. The current-voltage measurement of the NiO/Si heterostructure exhibited rectifying characteristics with enhanced photocurrent under light illumination. Photodetection capability was measured in the range from 300 nm to 800 nm, and a higher photoresponse in the UV region was observed due to the wide bandgap of NiO. The presence of a top graphene transparent conducting electrode further enhanced the responsivity in the whole measured wavelength region from 350 to 800 nm. The photoresponse of the NiO/Si detector at 350 nm was found to increase from 0.0187 to 0.163 A/W at -1 V with the insertion of the graphene top layer. A high photo-to-dark current ratio (≃104) at the zero bias indicates that the device has advantageous application in energy-efficient high-performance broadband photodetectors.

Resonant-cavity-enhanced 4H-SiC thin film MSM UV photodetectors on SiO2/Si substrates

Heterogeneous integration of 4H-SiC film with Si substrate can produce ultraviolet (UV) photodetectors (PD) with higher performance and easier integration with silicon CMOS circuits than homogenous epitaxy of 4H-SiC on SiC substrates. In this study, 1.2 µm thick high-quality single crystalline 4H-SiC thin films were successfully bonded with SiO2/Si (100) substrates using the Smart-Cut technique, achieving bubble-free bonding interfaces and 6.03 MPa bonding strength. UV PDs of metal–semiconductor–metal type with a resonant cavity structure were fabricated for the first time using the heterogenous film sample. The device exhibits a low dark current of 1.6 × 10−13 A in reverse bias of 20 V and a maximum specific detectivity of about 5.2 × 1012 Jones at 280 nm, which is significant for a device with a resonance-enhanced structure. These results demonstrate a promising approach for the fabrication of 4H-SiC devices with silicon CMOS circuits.

Enhancing ferroelectric performance in hafnia-based MFIS capacitor through interface passivation and bulk doping

In recent times, there has been a notable surge of interests in hafnia (HfO2)-based ferroelectrics, primarily due to their remarkable ferroelectric properties employed in ultra-thin configurations, alongside their compatibility with the conventional CMOS manufacturing process. In order to harness the full potential of HfO2-based films for high-performance non-volatile memory applications, it is imperative to enhance their ferroelectric characteristics and durability. This study introduces a straightforward approach aimed at augmenting the ferroelectric performance of Hf x Zr1−x O2 (HZO) films deposited on silicon (Si) substrates through the engineering of oxygen vacancies (V O). The results of this endeavor demonstrate a significant enhancement in ferroelectric performance, characterized by a 2Pr value of 47 μC cm−2 and impressive endurance, enduring up to 108 cycles under an 8 MV cm−1 electric field without the need of a wake-up process. This marked improvement can be attributed to a dual-pronged approach, involving the incorporation of an Al2O3 interlayer and the introduction of Al atoms into the HZO film. The Al2O3 interlayer primarily serves to mitigate the presence of oxygen vacancies at the interface, while the introduction of Al dopants elevates the concentration of oxygen vacancies within the bulk material. This modulation of oxygen vacancy concentration proves instrumental in facilitating the formation of a ferroelectric o-III phase within the HZO-based films, thereby further augmenting their ferroelectric performance. This innovative and effective strategy offers an alternative avenue for enhancing the ferroelectric properties of materials characterized by a fluorite crystal structure.

Energization‐Time Dependence of Electrical Properties of Anodized n‐GaN Grown on Si Substrates

With a view to device applications as a new material, n‐GaN grown on Si substrates is anodized at 4 V in an electrolyte solution for different energization times (15–240 min), and the dependence of the changes in electrical properties on the anodization time is evaluated. Anodization at 4 V increases the resistivity of n‐GaN with increasing energization time. To investigate the origin of the increase in resistivity by anodization, the results of the temperature dependence of the Hall mobility and electron density are discussed. The Hall mobility decreases with increasing energization time. The decrease in Hall mobility is because anodization forms neutral defects and increases neutral‐impurity scattering. The electron density decreases with increasing energization time. The decrease in electron density occurs because anodization deepens the original donor level and generates a deeper level that captures electrons. Thus, anodization changes the electrical properties of n‐GaN grown on Si substrate, and their dependence on energization time is discussed in detail.

Ferroelectric polycrystalline Bi2SiO5 thin films on Pt-covered Si substrates prepared by pulsed laser deposition combined with post-annealing

In this study, we report on the fabrication of polycrystalline thin film Bi2SiO5, a notable non-perovskite ferroelectric material. The thin films were deposited on Pt-covered Si substrates by pulsed laser deposition (PLD) at room temperature, followed by a post-annealing process in air. The as-deposited thin film was of an amorphous phase of Bi-Si-O, and turned to a polycrystalline phase of Bi2SiO5 by the post-annealing above 550°C. The influences of the post-annealing temperature on the phase preference, surface morphology, and dielectric properties of the thin films were investigated by Raman spectroscopy, X-ray diffraction (XRD), atomic force microscopy (AFM), and dielectric measurements. As a result, the optimal post-annealing temperature was determined to be 600°C, yielding a good ferroelectric polycrystalline Bi2SiO5 thin film with a relative dielectric constant of 143 and a remanent polarization (2Pr) of 7.2 μC cm−2.

Fabrication and characterization of magnetron sputtered SAC305 thin films

This study investigates the surface morphology, mechanical properties including the strain rate sensitivity of the hardness in indentation creep, and electrical resistivity of SAC05 (96.5 %Sn-3 %Ag-0.5 %Cu) thin films sputtered onto Si and SiO2 substrates using RF and DC magnetron. Various deposition parameters, including DC and RF powers and pressures, were optimized for a continuous and robust film. Among the 16 samples analyzed, the optimal surface was obtained at RF 200 W and 0.32 Pa pressure, as confirmed by FE-SEM. Before polishing, the film exhibited a rough surface with an average grain size of ∼1 µm a thickness of ∼2 µm. Post-polishing, the film displayed a uniform 1.5 µm thickness and a mean surface roughness (Ra) of 14.9 nm. The electrical resistivity of SAC305 on the SiO2 substrate was 19.6 µΩ.cm, while the strain rate sensitivity, m, for SAC305 on the Si substrate was 0.12 ± 0.02.

Effect of Deposition Working Power on Physical Properties of RF-Sputtered CdTe Thin Films for Photovoltaic Applications.

The main objective of this study was to determine the variation in the properties of cadmium telluride (CdTe) thin films deposited on a p-type Si substrate by the radio frequency magnetron sputtering technique at four different working powers (70 W, 80 W, 90 W, and 100 W). The substrate temperature, working pressure, and deposition time during the deposition process were kept constant at 220 °C, 0.46 Pa, and 30 min, respectively. To study the structural, morphological, and optical properties of the CdTe films grown under the mentioned experimental conditions, X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and optical spectroscopy were used. For a better analysis of the films' structural and optical properties, a group of films were deposited onto optical glass substrates under similar deposition conditions. The electrical characterisation of Ag/CdTe/Al "sandwich" structures was also performed using current-voltage characteristics in the dark at different temperatures. The electrical measurements allowed the identification of charge transport mechanisms through the structure. New relevant information released by the present study points towards 90 W RF power as the optimum for obtaining a high crystallinity of ~1 μm nanostructured thin films deposited onto p-Si and optical glass substrates with optical and electrical properties that are suitable for use as absorber layers. The obtained high-quality CdTe nanostructured thin films are perfectly suitable for use as absorbers in CdTe thin-film photovoltaic cells.

InN nanowire solar cells on Si with amorphous Si interlayer deposited by sputtering

Here, we report the first experimental demonstration of InN nanowire solar cells deposited by RF sputtering with a bandgap energy of 1.78 eV. By adding an amorphous Si (a-Si) buffer to the n-InN/p-Si structure, we have improved the photovoltaic performance of the resulting devices while maintaining their material quality. We have firstly optimized the deposition of Si on Si(100) by DC sputtering, obtaining an amorphous material with bandgap energy of 1.39 eV. Then we have studied the influence of the thickness of the a-Si buffer layer (0–25 nm) on the structural, morphological, electrical, and optical properties of InN nanowires on Si(100) substrates. With the use of a 15-nm buffer, n-InN/a-Si/p-Si nanowire heterojunction solar cells exhibit a promising short-circuit current density of 17 mA/cm2, open circuit voltage of 0.37 V and fill factor of 35.5%, pointing to a power-conversion efficiency of 2.3% under 1-sun (AM 1.5G) illumination. These work demonstrates that the combination of in-situ sputtered a-Si, which could serve as potential passivation layer, and the light trapping enhancement by the nanostructured active layer leads to an improvement of the photovoltaic efficiency of sputtered III-nitride devices.

Utilizing Island Growth in Superlattice Buffers for the Realization of Thick GaN‐on‐Si(111) PIN‐Structures for Power Electronics

In this study, the effect of implementing island growth in an AlN/Al0.1Ga0.9N superlattice on the structural properties of vertical GaN‐on‐Si(111) PIN‐structures is investigated. It is demonstrated by scanning electron microscopy (SEM) and atomic force microscopy (AFM) that islands are formed on‐top of V‐pits present in the AlN nucleation layer and that the island coalescence height can be controlled by the growth temperature. Defect selective etching analyses confirm a noteworthy reduction in the threading dislocation density (TDD), which diminishes from 1.2 × 109 cm−2 ± 7.5 × 107 cm−2 to 8.5 × 108 cm−2 ± 7.3 ×107 cm−2 as the island coalescence height increases from ≈160 nm to ≈450 nm, achieved by increasing the growth temperature. Cross‐sectional transmission electron microscopy (TEM) shows that island growth is particularly favorable for the reduction of a‐type dislocations. As a consequence of the significant reduction of a‐type dislocations in the buffer, stress relaxation during the GaN film growth is reduced, which is supported by in situ wafer curvature measurements and high‐resolution X‐ray diffraction (XRD). Owing to the optimized island growth conditions, thick and crack‐free GaN layers on Si(111) substrates are obtained with an absolute wafer bow of <50 μm.

Investigating Si (100) surface patterns as well as electrical states through integrating molecular dynamics simulations with density functional tight binding at atomic level

The present work performs molecular dynamics simulations within model potential’s framework to investigate surface atoms’ rearrangements, loading states, and stress distribution in Si (100) surface on heating, and then single point energy calculations for the obtained atomic packing structures of Si substrates are used to obtain electrical information through self-consistent charge density functional tight binding approach. From analysis of Lode-Nadai parameters, atomic stress, visually packing images, Mulliken charges of atoms, Mulliken electron populations on atomic orbitals, differential charge densities, and chemical potentials for substrates, the knowledge of surface patterns, micro-loading states on the atoms and electrical states are obtained. The simulation results show the positions of vacancies have a significant impact on the rearrangements of the surface atoms. The appropriate selection of vacancy positions could be helpful in designing patterns of Si (100) surface. The vacancies in the subsurface or deeper atomic layers present migrations, where the migrations are more likely to occur at higher temperatures. There are stress concentration area and apparent charge transfers for the atoms forming dimers and neighboring atoms around the vacancies, and the differential charge densities in the surface atoms also present significant differences. These substrates with different surface patterns have different chemical potentials.

Highly sensitive on-skin flexible Sb2O3/Sb thin film pH sensor for real-time sweat sensing

This study presents a significant advancement in the application of a freestanding potentiometric pH sensor patch made of PDMS, incorporating a sensing electrode of Sb2O3/Sb thin film and a reference electrode of AgIO3/Ag thin film. The pH sensing electrodes of Sb2O3/Sb/Au/Ni and AgIO3/Ag/Au/Ni thin films were deposited over the PDMS/cellulose acetate/Si substrate using the ECR/RF sputtering technique. The pH sensor prepared on the PDMS/cellulose acetate/Si substrate displayed excellent sensitivity (−58.24 to −60.84 mV/pH, n = 4) and a robust linear response (R2 ∼ 0.99) in a wider pH range (1.68–9.18). The flexible on-skin wearable pH sensors were obtained by peeling off the pH sensor-assisted PDMS sheet from the Si substrate, which exhibited a remarkable sensitivity of -54.29 mV/pH and a linear pH response (R2 ∼ 0.99). Real-time sweat sensing experiments confirmed the accuracy of the developed flexible on-skin wearable pH sensors in monitoring pH levels at different body parts.

Asymmetric metamaterial sandwich structure with NIM characteristics for THz imaging application

This study presented a unique, miniaturised asymmetric interconnected vertical stripe (IVS) design for terahertz (THz) frequency applications. Therefore, this research aimed to achieve a frequency response of 0 to 10 THz using a 5 × 5 µm2 Silicon (Si) substrate material. Meanwhile, various parametric examinations were conducted to investigate variations in the performance. For example, the unit cell selection process was carefully examined by using various design structures and modifying the structure by adding split gaps and connecting bars between vertical stripes. Furthermore, the proposed sandwich structure design was used to compute the absorbance and reflectance properties. All the analytical examinations were executed utilising the Computer Simulation Technology (CST) 2019 software. The introduced IVS metamaterial exhibits negative index behaviour and has a single resonance frequency of 5.23 THz with an acceptable magnitude of − 24.38 dB. Additionally, the quadruple-layer IVS structure exhibits optimised transmission coefficient behaviour between 3 and 6 THz and 7 to 9 THz, respectively. However, the magnitude of the transmission coefficient increased with the number of material layers. Besides that, the absorbance study shows that using a quadruple-layer structure obtains unique and promising results. Overall, the proposed asymmetric IVS metamaterial design achieves the required performance by using a compact structure rather than extending the dimensions of the design.

Remote epitaxy-based atmospherically stable hybrid graphene template for fast and versatile transfer of complex ferroelectric oxides onto Si

Heterogenous integration of complex epitaxial oxides onto Si and other target substrates is recently gaining traction. One of the popular methods involves growing a water-soluble and highly reactive sacrificial buffer layer, such as Sr3Al2O6 (SAO), at the interface and a functional oxide on top of this. To improve the versatility of layer transfer techniques, it is desired to utilize stable (less reactive) sacrificial layers without compromising on the transfer rates. In this study, we utilized a combination of chemical vapor deposited (CVD) graphene as a 2D material at the interface and pulsed laser deposited (PLD) water-soluble SrVO3 (SVO) as a sacrificial buffer layer. We then exploit the well-known enhancement of liquid diffusivities by monolayer graphene to enhance the dissolution rate of SVO over ten times without compromising its atmospheric stability. We demonstrate the versatility of our hybrid- graphene-SVO- template by growing ferroelectric BaTiO3 (BTO) via PLD and Pb(Zr, Ti)O3 (PZT) via Chemical Solution Deposition (CSD) technique and transferring them onto the target substrates and establishing their ferroelectric properties. Our hybrid templates allow for the realization of the potential of complex oxides in a plethora of device applications for MEMS, electro-optics, and flexible electronics.

The Influence of Mechanical Strains and Quantum-Size Effects on the Photosensitivity of Ge/Ge(x)Si(1-x) Nanofilm

Calculations of the maximum light wavelength of intrinsic absorption for the unstrained and strained germanium nanofilm were carried out. It was established that the photosensitivity of such nanofilm with the thickness of d 10 nm significantly depends on the effects of dimensional quantization and the magnitude of internal mechanical strains. It is shown that the variation of the thickness of the germanium nanofilm and the component composition of the Ge(x)Si(1–x) substrate allow controlling by its photosensitivity in the range from 0.8 to 4 μm.

Ion Bombardment-Induced Stress Mechanism for the Formation of Ag Nanotwinned Films on Si Substrates

Ion Bombardment-Induced Stress Mechanism for the Formation of Ag Nanotwinned Films on Si Substrates

Evolution of GeSi islands in epitaxial Ge-on-Si during annealing

Epitaxial growth of Ge on Si has been widely studied for photonic and electronic applications. However, GeSi interdiffusion during the growth or annealing deteriorates the performance of the devices. This paper explores the evolution of the interface and GeSi interdiffusion upon post-annealing. We found the GeSi interdiffusion islands with concentration plateaus gradually disappeared upon annealing and the interdiffusion became more pronounced in the Ge layer. Moreover, by using a thin layer of SiO2 as a reference, we directly visualized the Kirkendall phenomenon, i.e., the migration of the Ge/Si interface towards the Si substrate after the annealing. Effective interdiffusivity at 900 °C was extracted using Boltzmann-Matano analysis, which indicated that the GeSi interdiffusion at the interface was dominated by dislocation-mediated interdiffusion.