Plasma Enhanced Chemical Vapor Deposition Research Articles

Dynamics of Nonlinear Optical Losses in Silicon‐Rich Nitride Nano‐Waveguides

AbstractFree carrier absorption (FCA) is established to be the cause of nonlinear losses in plasma‐enhanced chemical vapor deposition (PECVD) silicon‐rich nitride (SRN) waveguides. To validate this hypothesis, a photo‐induced current is measured in SRN thin films with refractive indices varying between 2.5 and 3.15 when a C‐band laser light is illuminating the SRN films at various powers, indicating the generation of free carriers. Furthermore, nonlinear loss dynamics is, for the first time, measured and characterized in detail in SRN waveguides by utilizing high peak power C‐band complex shape optical pulses for estimation of free carrier generation (FCG) and free carrier recombination (FCR) lifetimes and their dynamics. Both FCG and FCR are found to decrease with an increase in the refractive index of SRN, and, specifically, the FCR lifetimes are found (92 ± 7) ns, (39 ± 3) ns, and (31 ± 2) ns for the SRN indices of 2.7, 3, and 3.15, respectively. Lastly, nonlinear losses in high refractive index SRN waveguides are demonstrated to be minimized and altogether avoided when the pulse duration reduced below the free carrier generation lifetime, thus providing a way of taking a full advantage of the large inherent SRN nonlinear properties.

Correlation study of graphitic shell encapsulated nickel: A multi-spectroscopic approach

Graphite-encapsulated metal nanoparticles hold great potential across various applications due to their unique combination of metal and graphitic properties. While Raman spectroscopy is widely used to assess the graphitic shells, metrics derived from prominent Raman bands often prove unreliable when analyzing such structures with a large number of heterogeneous flakes and are mostly applicable to few-layer graphene. However, researchers continue to face challenges in identifying reliable metrics that accurately reflect two key properties of graphitic shells: thickness and degree of graphitization. In this study, graphitic shells were synthesized via plasma-enhanced chemical vapor deposition (PECVD) at low temperatures (500 °C), seeded by nickel nano-islands. A full-factorial experiment was designed to explore a diverse sample space by varying two key input factors: the initial thickness of the nickel seeding film and the duration of carbon deposition. Using resource-intensive surface characterization techniques (SEM, EDS, XPS, and AFM), we verified encapsulation efficiency and morphology, identifying strong correlations between the input factors and properties of the shells. To gain insights into structural characteristics, we employed conventional spectroscopy techniques (Raman, UV–Vis-nIR transmission, and Transient Absorption Spectroscopy), introducing 107 metrics derived from spectral data. Principal Component Analysis (PCA) aligned the input factors, and their corresponding shell properties, with the first two principal components. Accordingly, we identified the most relevant metrics including new candidates derived from less prominent Raman bands. Additionally, inter-metric correlations enable interchangeable use of spectroscopy techniques. This study marks the first multi-spectroscopic correlation analysis of graphitic shells and provides a novel framework for evaluating their properties.

Influence of Synthesis Parameters on Structure and Characteristics of the Graphene Grown Using PECVD on Sapphire Substrate.

The high surface area and transfer-less growth of graphene on dielectric materials is still a challenge in the production of novel sensing devices. We demonstrate a novel approach to graphene synthesis on a C-plane sapphire substrate, involving the microwave plasma-enhanced chemical vapor deposition (MW-PECVD) technique. The decomposition of methane, which is used as a precursor gas, is achieved without the need for remote plasma. Raman spectroscopy, atomic force microscopy and resistance characteristic measurements were performed to investigate the potential of graphene for use in sensing applications. We show that the thickness and quality of graphene film greatly depend on the CH4/H2 flow ratio, as well as on chamber pressure during the synthesis. By varying these parameters, the intensity ratio of Raman D and G bands of graphene varied between ~1 and ~4, while the 2D to G band intensity ratio was found to be 0.05-0.5. Boundary defects are the most prominent defect type in PECVD graphene, giving it a grainy texture. Despite this, the samples exhibited sheet resistance values as low as 1.87 kΩ/□. This reveals great potential for PECVD methods and could contribute toward efficient and straightforward graphene growth on various substrates.

Single-Step PECVD Synthesis of Graphene@Carbon Nanotubes Electrocatalyst.

Graphene (Gr) and carbon nanotubes (CNTs), the two intriguing carbon nanomaterials, have presented great potential in serving as high-performance electrocatalysts in lithium-sulfur (Li-S) chemistry. The concurrent management of both materials would achieve a promoted synergistic effect. Nevertheless, there still remains a lack of an effective material synthesis route. Herein, a single-step plasma-enhanced chemical vapor deposition (PECVD) strategy is devised to prepare Gr@CNTs heterostructures with strong bonded connections. In the PECVD system, the damaged sidewalls generated in CNT tubes can serve as appropriate nucleation sites for further Gr growth. The formation mechanisms are thoroughly explored in aspects of both experimental characterizations and theoretical calculations. To confirm the validity of this approach, thus-constructed Gr@CNTs architectures are employed as the sulfur host, enabling boosted redox kinetics of polysulfides. This project provides fundamental insight into the mechanism exploration for single-step PECVD growth of Gr@CNTs heterostructure, hence promoting the practical application prospect of carbon nanomaterials toward Li-S systems.

A study on the microstructure and power generation performance of colored BIPV modules

The need for greenhouse gas reduction and carbon neutrality is increasing, and the Building Integrated Photovoltaic (BIPV) power generation system is emerging as a key element. However, colored BIPV modules that enhance the aesthetic value of buildings have challenges in maintaining power generation efficiency due to their varied optical properties. This work investigates the structural, elemental, and power generation of colored BIPV modules fabricated using Plasma Enhanced Chemical Vapor Deposition (PECVD), inorganic pigment dyeing (HAZE), and color dot printing (DOT) in comparison to a conventional BIPV module without color treatment. Comprehensive structural and elemental analyses were performed, and optical properties were assessed. Power generation performance was measured using an Outdoor-exposed Power Generation Evaluation (OPGE) test at various tilt angles and azimuths. The results indicated a 57.2 % decrease in power output for the PECVD module, while the DOT and HAZE modules showed a reduction of approximately 30 % compared to the reference module. The power output of the colored modules decreased compared to the conventional ones due to higher light reflectance. However, to enhance efficiency, an improved optical design was developed, reducing light reflectance by over 57 % on average. This provides the potential for optimizing both the aesthetic and functional aspects.

Tunnel silicon oxynitride phase transformation for n-type polysilicon passivating contacts in crystalline silicon solar cells

The study investigates the fabrication and characterization of tunnel oxynitride (TON) layers produced using Plasma-Enhanced Chemical Vapor Deposition (PECVD) at different pressure and power variations. The aim is to explore TON layers as potential substitutes for conventional SiO2 in Tunnel Oxide Passivated Contact (TOPCon) solar cells. Foe this purpose, an effective oxide thickness (EOT) of 1.1–1.2 nm and 1.5–1.6 nm has been achieved by treating the TON samples with NH3 and N2 gas plasma, respectively. Fourier Transform Infrared Spectroscopy (FTIR) analysis revealed critical variations in the chemical bonding within TON layers, which exhibit different properties based on the deposition conditions. The presence of nitrogen-nitrogen and nitrogen–hydrogen bonds is prominently influenced by changes in the PECVD parameters, directly affecting the layer’s optical and electronic properties. Notably, the presence of hydroxyl (O–H) and amino (NH2) groups within the TON structure suggests an improvement in surface passivation, essential for optimizing solar cell performance and durability. A lifetime of 737 and 823 μs has been recorded for N2 and NH3 samples, compared to the NAOS 710 μs reference sample. NH3 plasma-treated samples show an improved iVoc of 736 mV, indicating better phase transformation and passivation quality than N2 plasma treatment and the NAOS reference sample.

Modeling and characterization of low frequency noise in self-aligned top-gate coplanar IGZO thin-film transistors

Abstract A modified low-frequency noise (LFN) model was proposed to accurately estimate the quality of the gate dielectric in self-aligned top-gate (SA TG) coplanar structure indium–gallium–zinc oxide (IGZO) thin-film transistors (TFTs). The proposed LFN model was derived by modifying the conventional carrier number with correlated mobility fluctuation model considering the peculiar characteristics of SA TG coplanar IGZO TFTs such as the channel length reduction due to the diffusion of hydrogen atoms or oxygen vacancies from the source/drain to the channel, as well as the relatively large source/drain parasitic resistance. The proposed model was validated by demonstrating that the measured LFN values were in good agreement with the predicted values from the proposed model for all SA TG coplanar IGZO TFTs with SiO2 gate dielectrics deposited under different plasma-enhanced chemical vapor deposition (PECVD) power densities. The near-interface gate dielectric trap densities extracted from each TFT using the proposed LFN model revealed a clear increase as the PECVD power increased, which is considered a major cause of poor positive-bias-temperature-stress stability of the SA TG coplanar IGZO TFT with SiO2 gate dielectric deposited under high PECVD power conditions.

Bulk acoustic wave—Solidly mounted resonator with a-SiOCN:H as low-Z material

Bulk acoustic wave (BAW) filters have been proven to be of high demand in today's low power RF front-ends for mobile communication devices. Within the launch of 5G applications worldwide, especially in the region of new radio (nr-1) up to 6 GHz, defined frequency bands require filters of wide bandwidths, while simultaneously featuring steep edges and high out-of-band rejection. Due to the coexistence with 4G LTE (long term evolution) wireless standards as well as advanced data transfer concepts such as carrier aggregation, the increasing complexity of antenna systems forces the implementation of highly selective acoustic filters. In contrast to the widely used surface acoustic wave (SAW) technology, BAW filters appear with superior performance for frequencies above 1 GHz. This work describes the fabrication of a BAW-solidly mounted resonator (BAW-SMR) with a tailored material system of a-SiOCN:H as a low impedance (low-Z) material integrated within its acoustic Bragg mirror. A direct comparison to the widely used low-Z material of SiO2 with an acoustic impedance of around 13 MRayl is demonstrated by two equal resonator stacks by replacing only the uppermost low-Z thin film of the acoustic reflector. A single-mask design was chosen with platinum as a bottom electrode to ensure the most equal growth conditions for the piezoelectric aluminum nitride (AlN) layers on both reflectors’ surfaces featuring either the tailored a-SiOCN:H or standard SiO2. The a-SiOCN:H thin films were deposited by plasma-enhanced chemical vapor deposition and the according acoustic impedance was priorly depicted to 7.1 MRayl, which could be exploited to achieve an increase in the effective coupling coefficient beyond 7% as well as a resonator bandwidth of more than 60 MHz.

Effect of SiCN thin film interlayer for ZnO-based RRAM.

This study investigates the effect of silicon carbon nitride (SiCN) as an interlayer for ZnO-based resistive random access memory (RRAM). SiCN was deposited using plasma-enhanced chemical vapor deposition (PECVD) with controlled carbon content, achieved by varying the partial pressure of tetramethylsilane (4MS). Our results indicate that increasing the carbon concentration enhances the endurance of RRAM devices but reduces the on/off ratio. Devices with SiCN exhibited lower operating voltages and more uniform resistive switching behavior. Oxygen migration from ZnO to SiCN is examined by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses, promoting the formation of conductive filaments (CFs) and lowering set voltages. Additionally, we examined the impact of top electrode oxidation on RRAM performance. The oxidation of the Ti top electrode was found to reduce endurance and increase low resistive state (LRS) resistance, potentially leading to device failure through the formation of an insulating layer between the electrode and resistive switching material. The oxygen storage capability of SiCN was further confirmed through high-temperature stress tests, demonstrating its potential as an oxygen reservoir. Devices with a 20 nm SiCN interlayer showed significantly improved endurance, with over 500 switching cycles, compared to 62 cycles in those with a 5 nm SiCN layer. However, the thicker SiCN layer resulted in a notably lower on/off ratio due to reduced capacitance. These findings suggest that SiCN interlayers can effectively enhance the performance and endurance of ZnO-based RRAM devices by acting as an oxygen reservoir and mitigating the top electrode oxidation effect.

Growth of nanocrystalline graphite and vertically aligned graphite nanowalls thin films and their transfer on flexible substrates for applications as electrochemical sensors for anthracene detection

Plasma-enhanced chemical vapor deposition (PECVD) allows the growth of nanocrystalline graphite (NCG)-type materials, such as N-doped bulk NCG and graphite nanowalls (GNW), on different substrates (silicon and copper) to develop flexible electrochemical sensors for anthracene detection. The carbonic materials were investigated using different techniques, including X-ray diffraction, small-angle X-ray scattering, scanning electron microscopy, X-ray photoelectron spectroscopy, cyclic voltammetry, and differential pulsed voltammetry (DPV). XRD analysis revealed different crystallinity features for both graphitic materials, as the N-NCG film presented higher lattice strain (1 %) and dislocation density (5.2 × 1012 cm−2), compared to the GNW film with a lattice strain of 0.2 % and dislocation density of 7 × 1011 cm−2. We also present a successful approach for developing flexible electrodes via transfer process from Cu to polyethylene (PE) substrate. The carbonic films were transferred onto flexible substrates via thermal treatment of the Cu foils with the PE layers, followed by Cu etching to reveal the carbon material as the sensing area of the flexible sensors. Electrodes based on N-NCG and GNW grown on silicon and those transferred to PE substrates were investigated at different anthracene concentrations by DPV. The results showed greater performance for anthracene determination in the case of N-NCG/Si, showing a sensibility of 0.8 A⋅M−1 than that of GNW/Si (0.0625 A⋅M−1). However, the flexible GNW/PE electrode exhibited an increased response in DPV in the presence of anthracene, resulting in a higher sensitivity (0.23 A⋅M−1) than that of N-NCG/PE (0.19 A⋅M−1). This behavior suggests the good electrochemical compatibility of the GNW film with the flexible polymeric substrate to obtain a flexible electrochemical sensor for anthracene detection.

Sustainable vertically-oriented graphene-electrode memristors for neuromorphic applications

Neuromorphic computing, an innovative field in electronic and computing engineering, aims to enhance computing paradigms by simulating brain processes. Memristors, a two-terminal device, hold promise in revolutionising neuromorphic architectures by circumventing the Von-Neumann bottleneck. The performance and applicability of memristors heavily rely on the materials and fabrication processes employed. Graphene exhibits unique properties that can be leveraged in memristor design. Moreover, graphene stands out as a material with the potential for large-scale, sustainable production through Plasma Enhanced Chemical Vapour Deposition (PECVD). Notably, the properties of graphene-electrode memristors vary with minor structural differences induced by different PECVD temperatures. This paper reports the synthesis of graphene electrodes by time- and cost-effective PECVD from a sustainable plant extract for memristors. In addition, this paper delves into investigating how these structural variations impact the properties of graphene memristors and explores their potential exploitation in neuromorphic applications for implementing the well-known Spike Timing Dependent Plasticity (STDP) learning mechanism. The paper also utilises the developed STDP learning to perform an unsupervised spike-based pattern classification task.

Analysis of the synergetic effect of process parameters of hydrogenated amorphous carbon deposition in plasma-enhanced chemical vapor deposition using machine learning

The synergetic effects of process parameters on hydrogenated amorphous carbon (a-C:H) films properties were quantitatively analyzed in plasma-enhanced chemical vapor deposition. Predictive models, created from experimental datasets and machine learning, indicate a synergetic effect between the H2 ratio and ion energy impacting on the substrate. At a H2 ratio of 75 %, etch rates of 200 nm/min were predicted, regardless of radio frequency (RF) bias. These rates decreased to 120–140 nm/min at lower H2 ratios, primarily depending on RF bias. Quadrupole mass spectrometry and Raman scattering were used to investigate the underlying mechanisms. High H2 ratios led to a greater presence of low-mass hydrogen-rich molecules in the plasma. The C2H3 radical intensity at a 75 % H2 ratio was 15 times greater than that at 0 % at an RF bias of 50 W, and similar trends were observed for other low-mass neutrals. The synergetic effects of H2 ratio and RF bias decreased the film's hydrogen content. Machine learning and those diagnostics revealed that ion bombardment induces dehydrogenation of a-C:H, influenced by hydrogen-rich species. This study demonstrates that machine learning can uncover complex plasma processes and optimize material synthesis.

Advanced spectroscopic methods for probing in-gap defect states in amorphous SiNx for charge trap memory applications

Silicon nitride (SiNx) serves as the charge trap layer in current 3D NAND flash memory devices. The precise formation mechanism and electronic structure of localized defect trap states in SiNx remain elusive. Here, we present a refined experimental methodology to elucidate the in-gap defect states and the band gaps in amorphous SiNx thin films. Our approach integrates high-resolution reflection electron energy loss spectroscopy (REELS) and spectroscopic ellipsometry (SE) for comprehensive analysis. By systematical analysis, we aim to provide a robust method for determining in-gap electronic states in SiNx. We investigated two different SiNx films prepared by plasma-enhanced chemical vapor deposition and sputtering. Our analysis revealed several distinct in-gap states and determined band gap energies. This approach not only provide advanced spectroscopic methods to characterize the defect electronic states in SiNx, but also applicable to other large band gap semiconductors or dielectrics to predict device-level characteristics for future devices.

Wettability-dependent dissolution dynamics of oxygen bubbles on Ti64 substrates

In this study, the dissolution of a single oxygen bubble on a solid surface, here Titanium alloy Ti64, in ultrapure water with different oxygen undersaturation levels is investigated. For that purpose, a combination of shadowgraph technique and planar laser-induced fluorescence is used to measure simultaneously the changes in bubble geometry and in the dissolved oxygen concentration around the bubble. Two different wettabilities of the Ti64 surface are adjusted by using plasma-enhanced chemical vapor deposition. The dissolution process on the solid surface involves two distinct phases, namely bouncing of the oxygen bubble at the Ti64 surface and the subsequent dissolution of the bubble, primarily by diffusion. By investigating the features of oxygen bubbles bouncing, it was found that the boundary layer of dissolved oxygen surrounding the bubble surface is redistributed by the vortices emerging during bouncing. This establishes the initial conditions for the subsequent second dissolution phase of the oxygen bubbles on the Ti64 surfaces. In this phase, the mass transfer of O2 proceeds non-homogeneously across the bubble surface, leading to an oxygen accumulation close to the Ti64 surface. We further show that the main factor influencing the differences in the dynamics of O2 bubble dissolution is the variation in the surface area of the bubbles available for mass transfer, which is determined by the substrate wettability. As a result, dissolution proceeds faster at the hydrophilic Ti64 surface due to the smaller contact angle, which provokes a larger surface area.

Fabrication of carbon-coated V2O5-x nanoparticles by plasma-enhanced chemical vapor deposition for high-performance aqueous zinc-ion battery composite cathodes

Fabrication of carbon-coated V2O5-x nanoparticles by plasma-enhanced chemical vapor deposition for high-performance aqueous zinc-ion battery composite cathodes

Patterned 3D-graphene for self-powered broadband photodetector

The remarkable ultra-wideband energy capabilities of zero-bandgap two-dimensional (2D) graphene have made it an outstanding material for photon absorption and charge carrier generation across a broad spectrum. However, atomically thick 2D-graphene only exhibits a light absorption efficiency of 2.3%, posing a challenge for graphene-based photodetectors to harness photon energy effectively. This study utilized plasma-enhanced chemical vapor deposition technology and a mask to create in situ patterned 3D-graphene/Si-based Schottky heterojunctions. The porous structure and natural nano-resonant cavities of the 3D-graphene enhanced the probability of light absorption, while the curved and sharp edges and corners of the patterned 3D-graphene concentrated the local electromagnetic field and induced localized surface plasmon resonance. Both theoretical and experimental analyses confirmed the improved light absorption mechanisms and charge transfer of photogenerated carriers under the built-in electric field. The photodetector based on the patterned 3D-graphene/Si Schottky structure exhibits excellent broadband response characteristics spanning from 380 to 1550 nm, with responsivity and specific detectivity of 68.47 A/W and 1.43 × 1012 Jones at a wavelength of 1550 nm. Furthermore, the photodetector demonstrated ultrafast microsecond-level response times (116/120 μs rise/fall times) along with exceptional stability and reliability. The potential applications of as-fabricated photodetector include logic devices such as “AND” and “OR” gates and information encryption. This research holds valuable scientific significance for the design of future optoelectronic devices and provides crucial insights and technical support for developing high-performance Si-based graphene detectors.

Narrowband Solar-Blind Photodetection of the Plasmonic (In0.3Ga0.7)2O3 Detector via the Synergetic Enhancement of Small-Sized Ag-Nanoparticle Photoabsorbance and Surface Modification.

Currently, research on Ag nanoparticles (AgNPs) predominantly focuses on UV/visible photodetection and UV emission, seemingly overlooking the significance of Ag in enhancing deep ultraviolet photon detection. In this work, (In0.3Ga0.7)2O3 thin films were fabricated by plasma-enhanced chemical vapor deposition. Due to the unique photoabsorbance characteristic and better interaction with photons of small-sized AgNPs, they effectively suppress the UVB absorbance caused by energy band engineering in the (In0.3Ga0.7)2O3 thin film while enhancing photoabsorbance in UVC due to the surface plasmon effect. Therefore, under the synergistic effect of enhanced photon absorbance and hot electron transfer, the performance of the detector is significantly improved, and its responsivity (R), external quantum efficiency, and detectivity (D*) are 193 mA/W, approximately 100%, and 1014 Jones, respectively, at a bias of -6 V. The fast response time and decay time are 634.6 and 194.1 ms, respectively; the rapid decay facilitated by AgNPs is attributed to the increased indirect recombination rate. AgNPs exhibit excellent narrowband response characteristics and absorbance properties in specific wavelength bands for the InGaO photodetector. This research lays the foundation for the practical application of localized surface plasmon resonance-enhanced photon-sensing capabilities.

Development of Novel Ternary Alloy of CSiSn for Low-Cost Next Generation Photovoltaics

The growing need for highly efficient solar cells calls for significant advancements in the development of a new material system to meet the needs of low-cost and low-cost production. Current multi-junction solar cell alternatives are more costly to produce. This research showcases the development and analysis of a novel ternary material system, The CSiSn (CST) alloy, which shows potential for creating low-cost material with high absorption in of solar spectrum. In this work, the following aspects regarding the CST material are investigated: 1) Material modeling using density functional theory, 2) electronic band structure estimations, 3) low-temperature material growth technique via Plasma Enhanced Chemical Vapor Deposition (PE-CVD) system; 4) advanced material and optical characterizations of CST alloys.

Free-standing cubic gauche nitrogen stable at 760 K under ambient pressure.

Cubic gauche nitrogen (cg-N) has received wide attention for its exceptionally high energy density and environmental friendliness. However, traditional synthesis methods for cg-N predominantly rely on high-pressure techniques or the utilization of nanoconfined effects using highly toxic and sensitive sodium azide as precursor, which substantially restrict its practical application. On the basis of the first-principles simulations, we found that adsorption of potassium on the cg-N surface exhibits superior stabilization compared to sodium. Then, we chose safer potassium azide as precursor for synthesizing cg-N. Through plasma-enhanced chemical vapor deposition treatment, the free-standing cg-N was successfully synthesized without the need for high-pressure and nanoconfined effects. It demonstrated excellent thermal stability up to 760 K, and then rapid and intense thermal decomposition occurred, exhibiting typical thermal decomposition behaviors of high-energy-density materials. The explosion parameters were also measured using laser-induced plasma spectroscopy. Our work has substantially promoted the practical application of cg-N as HEDMs.

Investigating the mechanism of enhancing interfacial adhesion of SiOx films on GaAs substrates through process optimization

In the manufacturing of GaAs-based quantum well (QW) lasers, the adhesion between the Silicon dioxide (SiOx) film layer and the Gallium arsenide (GaAs) substrate is crucial for the performance and durability of semiconductor devices. This study focused on depositing SiOx films on GaAs substrates using plasma-enhanced chemical vapor deposition (PECVD). The research aimed to investigate the impact of different coating processes on the deposition rate, properties, and composition of the coatings. The interfacial adhesion of various samples was assessed using nano-scratch tests. The results revealed that samples with lower SiH4 gas flow and RF power, or higher process pressure exhibited stronger adhesion strength. It's further observed that optimizing the process parameters reduced residual stresses in the film, thereby enhancing the GaAs-SiOx interfacial bonding. This work has the potential to significantly reduce the possibility of QW lasers malfunctions, improve the reliability of semiconductor devices and provide valuable insights for future studies on enhancing film-substrate adhesion.