Thin SiO2 Research Articles

Strong Er3+ radiative emission enhancement by quasi-BIC modes coupling in all-dielectric slot nanoantenna arrays

We have designed and realized all-dielectric lossless nanoantennas, in which a thin SiO2 layer doped with erbium ions is placed inside slotted silicon nanopillars arranged in a square array. The modal analysis has evi-denced that the slotted nanopillar array supports optical quasi-BIC resonances with ultra-high Q-factors (up to Q∼109), able to boost the electromagnetic local density of optical states in the optically active layer. Up to 3 orders of magnitude photoluminescence intensity increment and 2 orders of magnitude decay rate enhancement have been measured at room temperature when the Er3+ emission at about λ=1540 nm couples with the quasi-BIC resonances. Furthermore, by tailoring the nanopillar aspect ratio, the slot geometry has been exploited to obtain selective enhancements of the electric or magnetic dipole contribution to Er3+ radiative transitions in the NIR, keeping the emitter quantum efficiency almost unitary. Finally, by computing the angularly resolved elec-tromagnetic field enhancement inside the nanoslot, the nanoantenna directivity has been designed, proving that strong beaming effects can be obtained. Our findings have a direct impact on the development of bright and effi-cient photon sources operating at telecom wavelength that are of primary importance for quantum nanophotonic applications.

Multimodal Encapsulation to Selectively Permeate Hydrogen and Engineer Channel Conduction for p-Type SnOx Thin-Film Transistor Applications.

It has been challenging to synthesize p-type SnOx (1 < x < 2) and engineer the electrical properties such as carrier density and mobility due to the narrow processing window and the localized oxygen 2p orbitals near the valence band. Herein, we report on the multifunctional encapsulation of p-SnOx to limit the surface adsorption of oxygen and selectively permeate hydrogen into the p-SnOx channel for thin-film transistor (TFT) applications. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) measurements identified that ultrathin SiO2 as a multifunctional encapsulation layer effectively suppressed the oxygen adsorption on the back channel surface of p-SnOx and selectively diffused hydrogen across the entire thickness of the channel. Encapsulated p-SnOx-based TFTs demonstrated much enhanced channel conductance modulation in response to the gate bias applied, featuring higher on-state current and lower off-state current (on/off ratio > 103), field effect mobility of 3.41 cm2/(V s), and threshold voltages of ∼5-10 V. The fabricated devices show minimal deviations as small as ±6% in the TFT performance parameters, which demonstrates good reproducibility of the fabrication process. The relevance between the TFT performance and the effects of hydrogen permeation is discussed in regard to the intrinsic and extrinsic doping mechanisms. Density functional theory calculations reveal that hydrogen-related impurity complexes are in charge of the enhanced channel conductance with gate biases, which further supports the selective permeation of hydrogen through a thin SiO2 encapsulation.

Si nanoplates prepared by ball milling photovoltaic silicon sawdust waste as lithium-ion batteries anode material

High-purity Si sawdust waste from the photovoltaic industry is an available source for Si anodes of lithioum-ion batteries (LIBs), but seeking for a synthetic process featuring with low cost and industrial scale from the Si waste to nanoscale Si materials in actual applications is quite challenging. Herein, we report a highly scalable and cost-effective ball milling method that directly converts photovoltaic Si sawdust waste to Si nano-plate (BM Si) for LIBs’ anode material. In the ball milling process, a thin SiO2 layer generates on BM Si. The nanoscale size of BM Si and SiO2 layer can buffer volume change of Si anode during cycling. As a result, BM Si displays a high initial capacity of 2196 mAh/g and remains a stable capacity of 1480 mAh/g after 100 cycles at 100 mA g−1, which is higher than that of commercial Si nanoparticles.

Spray-coated SiO2/PECVD SiN[formula omitted] stack for the passivation of n[formula omitted] emitter of p-type Si solar cell

Inefficient passivation of phosphorous diffused emitter is one of the limiting factors contributing to lower efficiency in advanced p-type silicon solar cells. Stack of SiO2 and SiNx with the former as an intermediate layer beneath SiNx provides better emitter passivation in comparison to SiNx film alone. Thermal oxide is reported to provide the best passivation, but it is not industrially viable. We demonstrate spray SiO2/SiNx as a viable alternative to thermal SiO2/SiNx stack. A few nanometer thin (∼6.1 nm) spray SiO2 film was first time demonstrated on micrometer sized textured pyramid with full coverage over an entire deposited area. The passivation of symmetrical (n+-p-n+) structure shows iVoc∼660 mV and passivation uniformity over the entire wafer area for both the stacks. Voc∼630 mV is achieved on cells with spray and thermal SiO2 as a passivating layer. Similar front passivation is further verified by overlapping IQE in the shorter wavelength range. Therefore, incorporating SiO2 film deposited via an industrially viable spray-coating process as a passivating layer at the front provides overall cell performance similar to the thermally grown SiO2.

Non-Equilibrium Growth of Surface Wrinkles Emerging in an SiO2/Si Stack during Si Melting Induced by UV Nanosecond Pulsed Laser Annealing

UV nanosecond pulsed laser annealing (UV-NLA) is demonstrating clear benefits in the emerging 3D-integrated electronic devices, where the allowed thermal budget is strictly limited to preserve underlying device performance. A possible drawback of UV-NLA is that melting a solid substrate covered by a dielectric layer, which can be found in typical CMOS device structures, induces wrinkles on the surface and may be an issue for subsequent processes. In this study, UV-NLA is performed in thermally-grown SiO2/Si structures to systematically investigate the formation of wrinkles. A classical analytical model adopted from literature shows a good agreement with our experimental results if a fitting coefficient is involved. Interestingly, its value is rapidly increasing for a thinner (roughly less than 50 nm) SiO2 film, whereas it becomes closer to unity for a thicker (roughly greater than 50 nm) SiO2 film. This might infer a possible discrepancy of the material properties taken from literature and those of real industrial thin SiO2 films. The impact of the as-grown SiO2 film stress on the growth of wrinkles is also investigated, improving the statistics of the measurements. The results do not show any significant impact possibly because of the degree of the as-grown SiO2 film stress being negligible compared to the SiO2 shear modulus.

Ion Drift and Polarization in Thin SiO2 and HfO2 Layers Inserted in Silicon on Sapphire.

To reduce the built-in positive charge value at the silicon-on-sapphire (SOS) phase border obtained by bonding and a hydrogen transfer, thermal silicon oxide (SiO2) layers with a thickness of 50–310 nm and HfO2 layers with a thickness of 20 nm were inserted between silicon and sapphire by plasma-enhanced atomic layer deposition (PEALD). After high-temperature annealing at 1100 °C, these layers led to a hysteresis in the drain current–gate voltage curves and a field-induced switching of threshold voltage in the SOS pseudo-MOSFET. For the inserted SiO2 with a thickness of 310 nm, the transfer transistor characteristics measured in the temperature ranging from 25 to 300 °C demonstrated a triple increase in the hysteresis window with the increasing temperature. It was associated with the ion drift and the formation of electric dipoles at the silicon dioxide boundaries. A much slower increase in the window with temperature for the inserted HfO2 layer was explained by the dominant ferroelectric polarization switching in the inserted HfO2 layer. Thus, the experiments allowed for a separation of the effects of mobile ions and ferroelectric polarization on the observed transfer characteristics of hysteresis in structures of Si/HfO2/sapphire and Si/SiO2/sapphire.

Modeling effective thermal conductivity enhanced by surface waves using the Boltzmann transport equation

The thermal management of semiconductors at the device level has become a crucial issue owing to the high integration density and miniaturization of microelectronic systems. Because surface phonon polaritons (SPhPs) exhibit long propagation lengths, they are expected to contribute significantly to the heat dissipation in microelectronic systems. This study aims to numerically estimate the heat transfer due to SPhPs in a thin SiO2 film. The one-dimensional Boltzmann transport equation (BTE) is solved using the estimated propagation length based on the SPhP dispersion curves. The temperature profiles and heat fluxes are predicted and demonstrate the size effect of the film on the effective in-plane thermal conductivity of the SiO2 film. The results indicate that the temperature distribution was constant regardless of the film length and thickness because the propagation length was much longer than the film length. In addition, the heat flux increased with decreasing film thickness owing to the depth-averaged energy transfer. The effective thermal conductivities predicted using the BTE differed by ~ 16.5% from the values obtained from the analytical expression. The numerical results of this study can provide valuable data when studying the thermal behavior of SPhPs.

Engineering a sandwiched Si/I/LNOI structure for 180-GHz-bandwidth electro-optic modulator with fabrication tolerances.

Electro-optical modulators are essential for scalable photonic integrated circuits and are promising for many applications. The convergence of silicon (Si) and lithium niobate (LN) allows for a compact device footprint and large-scale integration of modulators. We propose a sandwiched Si/I/LNOI modulator for broad modulation with CMOS-compatible fabrication tolerances. There is a thin film SiO2 spacer sandwiched between Si and LN, which is engineered to tailor optical and electrical properties and enhance index matching. Moreover, the SiO2 spacer is also exploited to inhibit the radiation loss induced by mode coupling. The modulator shows a bandwidth of ∼180 GHz with a halfwave voltage of 3 V. Such a device is considerably robust to the fabrication deviations, making it promising for massive and stable manufacturing.

In‐situ Lithiated SiO2 as Lithium‐Free Anode for Lithium‐Sulfur Batteries

AbstractLithium‐sulfur (Li−S) batteries are attractive owing to their high energy density and cost‐effectiveness. However, the practical application of Li−S batteries is hindered by uncontrollable lithium dendrite growth and severe polysulfide shuttling during cycling. Here, we fabricated 100 nm thin SiO2 decorated on carbon cloth (SiO2@CC). It is observed that in‐situ lithiation of SiO2 forms a highly lithiophilic LixSiOy layer over SiO2 which further acts as an efficient host for dendrite‐free lithium metal deposition. So lithiated SiO2@CC shows high affinity for homogenous growth of Li while the carbon fibers control the volume change during the deposition/stripping process. Hence, the synergistic effect of LixSiOy layer and carbon cloth (CC) effectively suppresses dendritic Li growth. As a result, the symmetric cell exhibits an ultra‐stable cycling performance over 1000 h with a low overpotential of &lt;25 mV even at a high current density of 1 mA cm−2. Further, the lithiated SiO2@CC is used as a lithium metal‐free anode (also a flexible electrode) for Li−S battery, which exhibits a stable capacity of 800 mAh g−1 over 500 cycles due to its unique structural properties. This work offers new insights and paves the way for developing dendrite‐free, high‐performance Li−S battery technology.

Carbon Nanotube-Fastened Graphene Composites with Bubble-Induced Multireflections for Electromagnetic Interference Shielding with Water Repellence

The use of light and flexible electromagnetic interference (EMI) shielding materials, particularly those considered for water repellence, is crucial in managing radiation pollution for modern electronic devices. However, the limited flexibility, weight, and water repellence of available shields constrain their applications. Herein, we demonstrated the potential of a carbon nanotube-fastened graphene composite film for EMI shielding, whose surface is adhered by a thin hydrophobic SiO2 coating. The reduced graphene with a curve and fastened morphology could be stored and form interconnected bubbles in the interior. Thus, the obtained film with flexibility and a thin thickness presents extremely high EMI shield performance of 76.4 dB due to anomalous multireflections in the interconnected bubbles, essentially different from shields that mainly reflect electromagnetic waves on a surface. In addition, the reliable roughness results in strong adhesion of the hydrophobic coating on a surface and demonstrates stable water repellence, even in severe conductions. The superhydrophobic film is a promising shield that could solve critical pollution for modern electronic devices.

Green synthesis of blue-green photoluminescent β-SiC nanowires with core-shell structure using coconut shell as carbon source

This work proposes a green method for synthesizing SiC nanowires (NWs) via the chemical vapor deposition (CVD) technique using coconut shell and silicon as raw materials. Using coconut shell as carbon source decreases the synthesis temperature of SiC. A large number of core-shell SiC NWs were obtained after firing at 1200 °C, a thin SiO2 layer is distributed on the outer shell of SiC NWs. The synthesized SiC NWs grow along the [111] direction, up to dozens of micrometers in length and diameters of 10–75 nm. However, the chain-bead structure of SiC NWs is formed after firing at 1400 °C due to the SiO2 bead embedded in SiC NWs. The synthesized core-shell SiC NWs fired at 1200 °C emit strong violet-blue light, which has good application prospects in optoelectronic devices.

Demonstration of Heterogeneous Structure for Fabricating a Comb-Drive Actuator for Cryogenic Applications.

This study presents an experimental demonstration of the motion characteristics of a comb-drive actuator fabricated from heterogeneous structure and applied for cryogenic environments. Here, a silicon wafer is anodically bonded onto a glass substrate, which is considered to be a conventional heterogeneous structure and is commonly adopted for fabricating comb-drive actuators owing to the low-cost fabrication. The displacement sensor, also with comb-finger configuration, is utilized to monitor the motion characteristics in real time at low temperatures. The irregular motions, including displacement fluctuation and lateral sticking, are observed at specific low temperatures. This can be attributed to the different thermal expansion coefficients of two materials in the heterogeneous structure, further leading to structural deformation at low temperatures. The support spring in a comb-drive actuator is apt to be deformed because of suspended flexible structures, which affect the stiffness of the support spring and generate irregular yield behavior. The irregular yield behavior at low temperatures can be constrained by enhancing the stiffness of the support spring. Finally, we reveal that there are limited applications of the heterogeneous-structure-based comb-drive actuator in cryogenic environments, and simultaneously point out that the material substrate of silicon on the insulator is replaceable based on the homogeneous structure with a thin SiO2 layer.

Increased Mobility in 4H-SiC MOSFETs by Means of Hydrogen Annealing

Enhancement-mode 4H-SiC MOSFETs utilising an aluminium oxide (Al2O3) dielectric without the requirement for an underlying silicon oxide (SiO2) layer have been shown to have a field effect mobility of 150 cm2V−1s−1 and a subthreshold swing of 160 mV/dec. The fabricated devices utilised a forming gas (3% H2 in N2) anneal immediately prior to the deposition of the Al2O3 by Atomic Layer Deposition (ALD). A comparison MOSFET using an identical Al2O3 deposition process with a 0.7 nm SiO2 layer had a field effect mobility of approximately 20 cm2V−1s−1. The hydrogen annealed device had a lower density of interface traps (Dit), a lower subthreshold swing, and a significantly reduced hysteresis in the transconductance data than the thin SiO2 sample. This finding solves the issue of inconsistency of device performance using thin film gate dielectric as an interfacial layer by offering a simple and controllable process.

Open volume defects in ultra-thin TiO2 layers embedded in VMCO-like samples studied with positron annihilation spectroscopy

Positron annihilation signals from VMCO-like samples grown by atomic layer deposition at different temperatures are utilized for the characterization of differences in open volume defects in TiN/TiO2/a-Si heterostructures. Doppler and coincidence Doppler mode of positron annihilation spectroscopy combined with a monoenergetic positron beam were used for this study. Differences observed in the Doppler parameters indicate differences in the positron trapping states of the TiO2 epilayers grown at different temperatures. Furthermore, the coincidence-Doppler results show that these differences cannot be due to intermixing of the TiO2 and a-Si layers and formation of thin SiO2 layers at the interface during the growth process. The results indicate that the amount of open volume defects in the TiO2 layer of the VMCO-structure seems to increase with an increase in the growth temperature.

Role of SiO2 Coating on YAG:V3+,Nd3+ Nanoparticles in Luminescence Thermometry

Coating luminescent nanoparticles with a SiO2 shell provides numerous benefits, which include improving the dispersibility of nanoparticles, reducing their cytotoxicity, and facilitating their biofunctionalization. However, from the perspective of luminescent thermometry, it is important that such a procedure does not alter the thermometric properties of the luminescent nanothermometer. Therefore, in this work, the effect of the SiO2 encapsulation procedure on the thermometric properties of YAG:V3+,Nd3+ nanoparticles was investigated. It was demonstrated that increasing the thickness of the SiO2 layer increases the thermal stability of the luminescence of V3+ ions. However, it was demonstrated that a high relative sensitivity of 1.5%/K at 500 K can be maintained for a luminescence thermometer while keeping a thin SiO2 shell.

Nonvolatile memory characteristics associated with oxygen ion exchange in thin-film transistors with indium-zinc oxide channel and HfO2-x gate oxide

Non-charge-storage-based nonvolatile memory characteristics associated with oxygen ion exchange are demonstrated in a thin-film transistor (TFT) composed of an indium-zinc oxide (IZO) channel and an oxygen-deficient HfO2–x gate oxide. A nonvolatile increase in drain current and a reduced threshold voltage are obtained upon application of positive gate voltage, with the opposite characteristics upon application of negative voltage. The device shows nonvolatile retention properties and suitable endurance properties after repeated operations. Modulation of channel conductance occurs as a results of oxygen ion exchange between the HfO2–x gate oxide and the IZO channel, which consequently alters the oxygen vacancy concentration in the IZO channel; these vacancies act as n-type dopants. For comparison, a device with a thin SiO2 layer inserted between the HfO2–x gate oxide and the IZO channel to prevent oxygen ion exchange shows only the increased threshold voltage upon application of a positive gate voltage as a result of electron charging. These results verify the conductance modulation mechanism associated with oxygen ion exchange at the interface of the HfO2–x gate oxide and the IZO channel. In addition, the nonvolatile memory characteristics of the device are indicative of its potential for non-charge-storage-based nonvolatile memory application.

Heterostructure Silicon Solar Cells with Enhanced Power Conversion Efficiency Based on Si x /Ni3+ Self-Doped NiO x Passivating Contact.

Developing efficient crystalline silicon/wide-band gap metal-oxide thin-film heterostructure junction-based crystalline silicon (c-Si) solar cells has been an attractive alternative to the silicon thin film-based counterparts. Herein, nickel oxide thin films are introduced as the hole-selective layer for c-Si solar cells and prepared using the reactive sputtering technique with the target of metallic nickel. An optimal Ni3+ self-doped NiOx film is obtained by tuning the reactive oxygen atmosphere to construct the optimized c-Si/NiOx heterostructure band alignment. A thin SiOx interlayer was further introduced to reduce the defect of the c-Si/NiOx interface with the UV–ozone (UVO) treatment. The constructed p-type c-Si/SiOx/NiOx/Ag solar cell exhibits an increase in the open voltage from 586 to 611 mV and achieves a 19.2% conversion efficiency.

An electron-selective SiC /SiO contact for Si solar cells made with fully industrial techniques

We explored the use of inline plasma-enhanced chemical vapor deposition (PECVD) to make P-doped poly-Si/SiO x -type contact for Si solar cells utilizing only industrially viable techniques, especially Ag metallization via screen-printing of a commercial fire-through paste. For this we used a thick (97 nm), non-blistering PECVD Si-rich SiC y layer, called SRC2.0, to minimize the damage due to the aggressive metallization process. The blistering suppression in SRC2.0 is achieved through the incorporation of carbon in the film but comes at the expense of its electrical conductivity. Despite this, ohmic contact between Si and SRC2.0/SiO x could be formed by annealing at 925 °C and higher. Moreover, we discovered that SRC2.0 has a detrimental effect on surface passivation with a thin (1.6 nm) SiO x layer that is typically used with poly-Si. This is due to reduction of the passivating SiO x layer during high-temperature annealing by the high amount (15%) of C in SRC2.0. Using a slightly thicker (1.9 nm) SiO x layer mitigated this effect, and J 0 values of 10 fA/cm 2 and lower (4 fA/cm 2 ), and 40 fA/cm 2 could be obtained in un-metallized and metallized regions, respectively. The best n-type Si solar cell with the SRC2.0/SiO x contact at the rear showed a very high short-circuit current density of 41.4 mA/cm 2 and a good open-circuit voltage of 688.4 mV. Its efficiency was, however, limited to 20.7%. This was due to the high specific contact resistance ((10–40) mΩ·cm 2 ) of the SRC2.0/SiO x contact, which in turn limited the fill-factor of the device to 72.6%. Nevertheless, the trends suggest that better device results can be obtained by using higher thermal budget. • PECVD SiC y layer compatible with industrial Si solar cell fabrication techniques. • SiC y /SiO x contact with screen-printed metallization using fire-through Ag paste. • J 0_pass of 10 fA/cm 2 together with J 0_metal of 40 fA/cm 2 has been demonstrated. • SiC y /SiO x contact employed at the rear of devices with B-diffused front contact. • The best device has a J sc of 41.4 mA/cm 2 , a V oc of 688.4 mV, and a FF of 72.6%.

Wake-up-free properties and high fatigue resistance of HfxZr1−xO2-based metal–ferroelectric–semiconductor using top ZrO2 nucleation layer at low thermal budget (300 °C)

Ferroelectricity and crystallinity of TiN/ZrO2/HfxZr1−xO2 (Hf:Zr = 0.43:0.57; HZO)/SiO2/Si metal–ferroelectric–semiconductor (MFS) capacitors with a top ZrO2 nucleation layer fabricated by low-temperature processes at 300 °C of atomic layer deposition and post-metallization annealing (PMA) were systematically investigated. The HZO (10 nm)-based MFS capacitors without (w/o) and with 2- and 10-nm-thick ZrO2 films (ZrO2-2 nm and ZrO2-10 nm, respectively) were found to form an extremely thin SiO2 interfacial layer (SiO2-IL) with a thickness of one or two monolayers. The HZO film in the TiN/ZrO2/HZO/SiO2/Si capacitors formed the ferroelectric orthorhombic phase even with a low thermal budget of 300 °C; in contrast, that of the w/o capacitor exhibited a predominantly amorphous structure. This result is attributed to the polycrystalline ZrO2 film acting as a nucleation layer for the crystallization of an amorphous HZO film during PMA treatment. Therefore, the remnant polarization (2Pr) increased in the order of w/o (2.2 µC/cm2) &amp;lt; ZrO2-2 nm (6.8 µC/cm2) &amp;lt; ZrO2-10 nm (15 µC/cm2). The endurance properties of the ZrO2-10 nm capacitor were free from the wake-up effect and exhibited less degradation because of the insertion of a thick ZrO2 film of 10 nm at the TiN/HZO interface, which promoted the preferential formation of the ferroelectric orthorhombic phase and prevented the formation of oxygen vacancies at the ZrO2/HZO interface. These results suggest that superior ferroelectricity with wake-up-free properties and higher fatigue resistance of HZO-based MFS capacitors can be achieved by a low-temperature fabrication technique (300 °C) using a top ZrO2 nucleation layer.

Monitoring electrode/electrolyte interfaces of Li‐ion batteries under working conditions: A surface‐enhanced Raman spectroscopic study on LiCoO2 composite cathodes

Lithium‐ion batteries are commonly used for electrical energy storage in portable devices and are promising systems for large‐scale energy storage. However, their application is still limited due to electrode degradation and stability issues. To enhance the fundamental understanding of electrode degradation, we report on the Raman spectroscopic characterization of LiCoO2 cathode materials of working Li‐ion batteries. To facilitate the spectroscopic analysis of the solid electrolyte interface (SEI), we apply in situ surface‐enhanced Raman spectroscopy under battery working conditions by using Au nanoparticles coated with a thin SiO2 layer (Au@SiO2). We observe a surface‐enhanced Raman signal of Li2CO3 at 1090 cm−1 during electrochemical cycling as an intermediate. Its formation/decomposition highlights the role of Li2CO3 as a component of the SEI on LiCoO2 composite cathodes. Our results demonstrate the potential of Raman spectroscopy to monitor electrode/electrolyte interfaces of lithium‐ion batteries under working conditions thus allowing relations between electrochemical performance and structural changes to be established.