Plasma-enhanced Chemical Vapor Deposition Technique Research Articles

Effect of the RF Power of PECVD on the Crystalline Fractions of Microcrystalline Silicon (μc-Si:H) Films and Their Structural, Optical, and Electronic Properties

In this work, we report on the deposition of microcrystalline silicon (µc-Si:H) films produced from silane (SiH4), hydrogen (H2), and argon (Ar) mixtures using the plasma-enhanced chemical vapor deposition (PECVD) technique at 200 °C. Particularly, we studied the effect of RF power on the crystalline fraction (XC) of the deposited films, and we have correlated the XC with their optical, electrical, and structural characteristics. Different types of characterization were performed in the µc-Si:H film series. We used several techniques, such as Raman scattering spectroscopy, Fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM), field emission scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM), among others. Our results show that RF power had a strong effect on the XC of the films, and there is an optimal value for producing films with the largest XC.

The quality studies of vertical graphene nanosheets catalyst-free microwave plasma-enhanced chemical vapor deposited on glass and fused silica

Vertical graphene nanosheets (VGN) were prepared by a microwave plasma-enhanced chemical vapor deposition technique on glass and fused silica. Their quality was explored by Raman scattering spectroscopy and transient absorption spectroscopy (TAS). We have observed a correlation between Raman scattering spectroscopy data and TAS parameters (charge carrier relaxation times and relative transient absorption signal amplitude). The substrate-related effects were explained by competition between the changes in the size of the effects induced by the graphene nanocrystallite, the substrate-induced graphene self-doping, and the presence of on-site and vacancy defects along with the dominant boundary defects. The optical and electrical properties of VGN on glass deposited at low substrate temperature (600 °C) were similar or even better compared to VGN on fused silica. The ability to prepare high-quality VGN on glass could be very attractive for practical application due to the low substrate price.

Effect of a-SiCxNy:H Encapsulation on the Stability and Photoluminescence Property of CsPbBr3 Quantum Dots.

The effect of a-SiCxNy:H encapsulation layers, which are prepared using the very-high-frequency plasma-enhanced chemical vapor deposition (VHF-PECVD) technique with SiH4, CH4, and NH3 as the precursors, on the stability and photoluminescence of CsPbBr3 quantum dots (QDs) were investigated in this study. The results show that a-SiCxNy:H encapsulation layers containing a high N content of approximately 50% cause severe PL degradation of CsPbBr3 QDs. However, by reducing the N content in the a-SiCxNy:H layer, the PL degradation of CsPbBr3 QDs can be significantly minimized. As the N content decreases from around 50% to 26%, the dominant phase in the a-SiCxNy:H layer changes from SiNx to SiCxNy. This transition preserves the inherent PL characteristics of CsPbBr3 QDs, while also providing them with long-term stability when exposed to air, high temperatures (205 °C), and UV illumination for over 600 days. This method provided an effective and practical approach to enhance the stability and PL characteristics of CsPbBr3 QD thin films, thus holding potential for future developments in optoelectronic devices.

Effect of film stress on different electrical properties of PECVD grown SiNx films and its bilayer structures: A study of Si surface passivation strategy

The prevalence of stress during thin film deposition has a substantial influence on the surface passivation of CMOS image sensors (CIS). Our present research thoroughly addresses the effect of film stress on minority carrier lifetime and interface trap density (Dit) of as-deposited and forming gas annealed (FGA, 5% H2, 400 °C for 30 min) SiNx films and their bilayer structures. In this study, plasma-enhanced chemical vapor deposition (PECVD) and atomic layer deposition (ALD) techniques were utilized to synthesize SiNx and SiNx/(top) Al2O3 bilayer structures. After FGA, the minority carrier lifetime and Dit values for 50 nm-SiNx (1607 μs, 7 × 1011 cm−2eV−1), 30 nm-Al2O3 (2670 μs, 7 × 1011 cm−2eV−1), 7 nm-SiNx/30 nm-Al2O3 (1750 μs, 6 × 1011 cm−2eV−1) and 50 nm-SiNx/30 nm-Al2O3 (2300 μs, 34 × 1011 cm−2eV−1) were found. Our statistical analysis indicates that the stress in the SiNx/Al2O3 bilayer structures introduces defects in the films. This affects the carrier lifetime along with Dit values and hence degrades CIS performance. Further, we also performed a stress simulation of SiNx films which corroborated with the overall analysis. We hope that this work facilitates a better understanding of the stress effect on the surface passivation of CIS applications.

Characterization of structural and mechanical properties of DLC films deposited on the surface of minute-scale 3D objects: Comparison of PECVD and FCVA deposition technique

Diamond-like carbon (DLC) films have received considerable attention owing to its excellent properties such as high hardness, low friction coefficient, high wear resistance, and chemical inertness. Because DLC film is considered an effective coating to improve the surface properties of materials, these films are used in various applications such as parts for automobile engines, hard disk surfaces, cutting tools and dies, and so on. The structure of the DLC film consists of a mixture of sp2- and sp3-bonded carbon atoms. Among them, the tetrahedral amorphous carbon (ta-C) film is known to be the hardest film owing to its diamond-like structure composed mainly of sp3-bonded carbon atoms. The most common deposition method for synthesizing ta-C is the filtered cathodic vacuum arc (FCVA) method. This method can remove the droplets that are non-ionic neutral species, and a high-quality film can be synthesized. However, the mechanical parts that require ta-C coating have a three-dimensional (3-D) shape, and it is difficult to coat the ta-C film on their entire surface conformity by the FCVA process. In this study, we deposited ta-C on three-dimensional parts by the FCVA method and evaluated the microstructure and surface morphology of the film in comparison with the plasma enhanced chemical vapor deposition (PECVD) method. Films were successfully coated over the entire surface of both millimeter- and nanometer-sized trench patterns. The film properties were investigated by Raman spectroscopy, SEM, nanoindentation tester and transmission electron microscopy.

Parasitic masking effect in GaN SA-MOVPE using SiO2 masks deposited by the PECVD technique

The paper reports a phenomenon of parasitic substrate masking during selective area metalorganic vapor phase epitaxy (SA-MOVPE) of gallium nitride (GaN) using silicon dioxide (SiO2) masks deposited by plasma enhanced chemical vapor deposition (PECVD) at pressures above 150 hPa. The discussion of the thermal stability and nitridation process of the SiO2 films is followed by the presentation of the experimental work results focused on the investigation of the relationship between the parasitic masking effect and pressure in the MOVPE reactor chamber. Analysis of the surface morphology is conducted using scanning electron microscopy (SEM) and atomic force microscopy (AFM). A hypothesis was proposed explaining the formation of the deposition-free region that indicates silanimine (HNSi) layer formation as a possible factor responsible for the adverse inhibition of GaN nucleation.

Fabrication of Aluminum Oxide Thin-Film Devices Based on Atomic Layer Deposition and Pulsed Discrete Feed Method

This study demonstrates the low-temperature (<100 °C) process for growing a thin silica buffer layer and aluminum oxide by atomic layer deposition (ALD) in the same reaction chamber. Heterogeneous multilayer thin films are prepared by a dual-mode equipment based on atomic layer deposition and plasma-enhanced chemical vapor deposition (PECVD) techniques. The pulse discrete feeding method (DFM) was used to divide the precursor purging steps into smaller intervals and generate discrete feeds, which improved the saturated distribution of gas precursors, film density and deposition selectivity. The experimental results show that the process method produces a uniform microstructure and that the best film uniformity is ±2.3% and growth rate is 0.69 Å/cycle. The thickness of aluminum oxide film has a linear relationship with the cyclic growth number from 360 to 1800 cycles. Meanwhile, the structural and mechanical stress properties of aluminum oxide thin films were also verified to meet the requirements of advanced thin-film devices.

Studies on Femtosecond Laser Textured Broadband Anti-reflective Hierarchical a-SiNx:H Thin Films for Photovoltaic Applications

Simple ultrafast laser writing for the fabrication of hierarchical silicon nitride (a-SiNx:H) microstructures is demonstrated as an effective antireflection coating. A wide range of Si-rich to N-rich a-SiNx:H thin films, having varied optical band gap (2.32–5.94 eV) and refractive index (2.8–1.7) of wavelength-ordered (∼λ/4) thickness, are deposited using the plasma-enhanced chemical vapor deposition technique. The high-intensity femtosecond laser (800 nm, 120 fs, 1 kHz) interaction with a-SiNx:H films resulted in diverse nano-/microstructures with systematic width and depth born out of nonlinear light–matter interactions. These experimentally demonstrated the extremely disordered micro–nano structures over a large area of ∼ 1 cm2 that exhibit significant light trapping and absorption capabilities over a broad spectral region of 200–1000 nm. The extensive reduction of reflection losses from 30 to 2.8% from pre- to post-laser texturing is a favorable condition for broadband anti-reflective coatings for enhanced light harvesting from prefabricated photovoltaic devices.

High-Translucency Zirconia Following Chemical Vapor Deposition with SiH4: Evidence of Surface Modifications and Improved Bonding.

To evaluate the effect of plasma-enhanced chemical vapor deposition (PECVD) with silicon hydride (SiH4) at different times on HT-zirconia surface characteristics and bonding of composite cement before and after thermocycling. Blocks of HT zirconia were obtained, polished, sintered and divided into five groups, according to PECVD time (n = 31): Zr-30 (30 s), Zr-60 (60 s), Zr-120 (120 s) and Zr-300 (300 s). The control group (Zr-0) did not receive PECVD. X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), energy dispersive spectroscopy (EDS) in conjunction with field-emission scanning electron microscopy (FE-SEM), x-ray photoelectron spectroscopy (XPS), goniometry, and profilometry tests were used for chemical and topographic characterization. Monobond N silane (Ivoclar Vivadent) was applied to the surface, and a cylinder of composite cement (Variolink N) was made (3 x 3 mm). Half of the specimens of each group were stored for 24 h or subjected to thermocycling (6 x 103 cycles). A shear bond strength (SBS) test was performed. Results were subjected to one-way ANOVA and Tukey's tests (α = 0.05). For experimental groups, XPS showed that formation of Si-O bonds contributed to increased surface free energy (SFE). FE-SEM and EDS showed that the longer the deposition time, the greater the amount of silicon on the surface. Zr-60 and Zr-300 presented higher and lower surface roughnesses, respectively. The silicon penetrated the microstructure, causing higher stress concentrations. The bond strength to composite cement was improved after all PECVD deposition times. The PECVD technique with SiH4, associated with chemical treatment with primer based on silane methacrylate, is a solely chemical surface treatment capable of maintaining bonding between composite cement and HT zirconia.

Chemical Vapor Deposition of Graphene on Self-Limited SiC Interfacial Layers Formed on Silicon Substrates for Heterojunction Devices

Direct chemical vapor deposition (CVD) of graphene on any desired substrate is always required to manufacture high-quality heterojunctions with excellent interfacial properties. Herein, the growth of graphene on cubic-silicon carbide (3C-SiC) surfaces using conventional high-temperature direct thermal CVD and plasma-enhanced CVD (PECVD) is explored, which is hardly reported to date. Since 3C-SiC substrates are not available, the controlled self-limited 3C-SiC layers on the Si(100) substrates were grown at different temperatures (900–1200 °C) via thermal-CVD technique to obtain virtual 3C-SiC substrates. The direct production of graphene via thermal CVD could not be achieved on such 3C-SiC surfaces. The density functional theory and molecular dynamics simulations confirm that the carbon atom diffusion over the 3C-SiC surface is extremely low, like over the Si surface, which leads to no graphene growth. A similar growth mechanism may be attributed to their similar crystal structure viz diamond cubic for Si and zinc blend for 3C-SiC. However, graphene nanowalls (GNWs) were successfully grown on both Si and 3C-SiC/Si surfaces at 700 °C via the PECVD technique, where similar surface morphologies were observed because the growth mechanism of GNWs is independent of substrate type. Moreover, I–V characterization was performed for different SiC/Si heterostructures and their corresponding GNWs/SiC/Si heterostructures, respectively. The current conduction improved considerably more for GNW/SiC/Si heterostructures as compared to SiC/Si heterostructures, but the creation of a SiC interfacial layer as well as its quality affected the conductivity of GNWs/SiC/Si heterostructures. The inevitable formation of an interfacial SiC layer during the direct graphene growth via thermal CVD on Si substrates can seriously affect the performance of graphene/Si heterojunction devices. Hence, PECVD growth of graphene is an ideal option to fabricate graphene/Si heterojunction devices with excellent interfacial properties or graphene/3C-SiC/Si heterojunction devices for various electronic/optoelectronic applications such as gas sensors and photovoltaic devices.

Development of Heterojunction c-Si/a-Si1-xCx:H PIN Light-Emitting Diodes.

In this work, we explored the feasibility of the fabrication of PIN light-emitting diodes (LEDs) consisting of heterojunctions of amorphous silicon-carbide (a-Si1-xCx:H) thin films and crystalline silicon wafers (c-Si). The objective is the future development of electro-photonic systems in the same c-Si wafer, containing transistors, sensors, LEDs and waveguides. Two different heterojunction LEDs were fabricated consisting of PIN and PIN+N structures, where a-Si1-xCx:H thin films were used as P-type and I-type layers, while an N-type c-Si substrate was used as an active part of the device. The amorphous layers were deposited by the plasma-enhanced chemical vapor deposition (PECVD) technique at a substrate temperature of 200 °C. The PIN device presented electroluminescence (EL) only in the forward bias, while the PIN+N device presented in both the forward and reverse biases. The EL in reverse bias was possible due to the addition of an N+-type a-Si:H layer between the c-Si substrate and the I-type a-Si1-xCx:H active layer. Likewise, the EL intensity of the PIN+N structure was higher than that of the PIN device in forward bias, indicating that the addition of the N-type a-Si:H layer makes electrons flow more efficiently to the I layer. In addition, both devices presented red EL in the full area, which is observed with the naked eye.

Plasma Deposition to Improve Barrier Performance of Biodegradable and Recyclable Substrates Intended for Food Packaging

The extensive application of biodegradable polymers in the food packaging industries was partially limited due to poor barrier performances. In the present work, we investigated the improvement of oxygen barrier performances by means of the deposition of a few nanometres of SiOx coatings on Poly(butylene succinate) (PBS) films. The coated samples produced by the plasma-enhanced chemical vapor deposition technique were tested in terms of morphology and composition of the surface and barrier properties. Barrier performances studied as a function of SiOx thickness were greatly improved and a reduction of at least 99% was achieved for oxygen transmission rate. In order to reduce the formation of residual stress between PBS substrate and SiOx coatings, a proper buffer layer (silicon organic SiOxCyHz) was used.

Performance of passivation layer for InP/InGaAs based short-wave infrared photodetector

The surface passivation effects of SiNx films deposited by plasma-enhanced chemical vapour deposition (PECVD) technique are investigated for InP/In0.53Ga0.47As mesa type photodetectors. It is found that the deposited SiNx film effectively reduces the densities of interface states (Dit) and slow trapped charge (Nt) near SiNx/In0.53Ga0.47As interface using NH4OH based pre-passivation treatment. The fixed charge density of 1.98 × 1011 C/cm2, the minimum value of Dit ∼3.2 × 1011 cm−2 eV−1 and Nt of 4.2 × 1011 C/cm2 are determined from the experimental capacitance-voltage curve of Ti–Au/SiNx/In0.53Ga0.47As based metal-insulator-semiconductor structure. Lower values of passivation properties indicate smaller surface recombination centre and lower surface leakage current. Thus, minimum noise related to dark current could be achieved for InP/In0.53Ga0.47As based mesa structured detector array with smaller pitch at room temperature.

Effect of low-pressure deposition on the mechanical and tribological properties of a-C:H films deposited via modified pulsed-DC PECVD with active screen as an additional cathode

Due to their attractive mechanical, chemical, tribological, and biological properties, diamond-like carbon (DLC) coatings are widely used in many industrial applications. Normally, the deposition of amorphous hydrogenated carbon (a-C:H) films is obtained via the plasma-enhanced chemical vapor deposition (PECVD) technique. Recently, a modified pulsed-DC PECVD technique has attracted attention in this field due to its making it possible to grow a-C:H films at low-pressures (up to 0.1 Pa) in a collision less regime, leading to the achievement of improved mechanical and tribological properties. The incorporation of an additional cathode allows the confinement of electrons and ions, stabilizing and densifying the cold plasma at much lower pressure than conventional PECVD systems. This method is distinguished by higher energy and acceleration of the C+ ions, simpler reactor system equipment, and lower operating cost. In the present investigation, hydrogenated amorphous carbon films were grown on AISI 316 stainless steel using a thin amorphous silicon interlayer to improve interface adherence. The characterization of the coatings allowed identifying the influence of the deposition pressure on the microstructural, mechanical, and tribological properties and the film's adherence. The main results indicate that obtaining films with high hardness, low compressive stress, low coefficient of friction, high wear resistance, and appropriate adhesion is possible at deposition pressures almost 100 times lower than conventional PECVD techniques.

Polarization-insensitive optical angular filtration enabled by defective photonic crystals

Optical angular filters, which can be used to filter light transmission at a specific angle, are extremely attractive for various optical applications. Here, we propose and experimentally demonstrate a one-dimensional (1D) defective photonic crystal (DPC) to realize polarization-insensitive narrow angular filtration at normal incidence. The proposed angular filter consists of a mirror-symmetric heterostructure incorporating two groups of alternatively stacked Si and SiO2 layers separated by a SiO2 defect layer. Using the plasma-enhanced chemical vapor deposition technique, the fabricated DPC can achieve a narrow angular transparency window of ±6° at the near-infrared wavelength. Based on the angular filtration effect, DPC angular filter is further demonstrated to suppress the diffraction phenomenon in the far-field projection imaging. We envision that the proposed angular filter based on DPC has potential applications in lens-less imaging, privacy protection, and beam shaping.

Inner surface modification of ureteral stent polyurethane tubes based by plasma-enhanced chemical vapor deposition to reduce encrustation and biofilm formation

Encrustation and/or biofilm formation in ureteral stents are major causes of obstruction and reduce the lifetime of a ureteral stent. In this study, the inner surfaces of polyurethane (PU) tubes (inner and outer diameters of 1.2 and 2.0 mm, respectively) were reformed with Ar, O2, and C2H2 gases using specialized plasma-enhanced chemical vapor deposition techniques for the first time. Then, the modified PU tubes were immersed in urine for 15 days, and the characteristics of the inner surfaces were analyzed. Depending on the modification procedure, the corresponding inner surface exhibited different chemical properties and different rates of encrustation and biofilm formation. For a hydrophilic surface treated with Ar and O2, encrustation and biofilm formation increased, while for the C2H2 coating, the development of encrustation and biofilm reduced by more than five times compared with the untreated bare PU tube. This study demonstrated that inner plasma surface modification of ureteral stents greatly enhances resistance to encrustation and biofilm formation.

Deposition of SrCO3 thin film consisting of self-assembled bundles of nanostructures by a plasma-enhanced liquid injection chemical vapour deposition technique

Deposition of SrCO3 thin film consisting of self-assembled bundles of nanostructures by a plasma-enhanced liquid injection chemical vapour deposition technique

Thermoelectrical properties of ternary lead chalcogenide plumbum-selenium-tellurium thin films with excess of tellurium prepared by plasma-chemical vapor deposition

Ternary chalcogenide PbSeTe thin films with sufficient excess of tellurium over the stoichiometry Pb50Se50-xTex have been fabricated by Plasma-enhanced chemical vapor deposition technique. High-pure elemental lead, tellurium, and selenium were the starting materials, that were supplied by the flow of high-pure argon into the 40 MHz inductively-coupled non-equilibrium plasma discharge at low pressure 13 Pa. Argon also served as the plasma-feed gas. The structural properties and chemical composition of the films were characterized by scanning electron microscope and X-ray diffraction analysis, respectively. The dependence of the Seebeck coefficient, resistivity and thermoelectric power factor on structural properties and composition were investigated. The influence of film composition on thermoelectric characteristics was studied.

Development of directly grown‐graphene–silicon Schottky barrier solar cell using co‐doping technique

Low-cost, highly efficient, and low-power devices are essential for energy harvesting applications. Despite numerous studies having been conducted on transferable graphene solar cells, large-area growth and long-term stability continue to remain elusive, which limits the practicability of graphene-based photovoltaic devices. Plasma-enhanced chemical vapor deposition is a promising, efficient, and facile method for synthesizing graphene over a large area without the use of a metal catalyst, but defects formed during graphene growth adversely affect the power conversion efficiency (PCE) of graphene/Si solar cells in which the graphene is used. In this work, we successfully employed acid-based graphene-Si macromolecular photovoltaic devices chemically doped with polymeric perfluorinated sulfonic acid (PFSA) macromolecules and nitric acid (HNO3). We achieved an improved PCE of about 9.27% with PFSA doping compared with the value (7.64%) without PFSA doping, and it increased substantially to 10.44% after co-doping with HNO3. PFSA macromolecular doping also led to a substantial increase in the carrier concentration, which helped to reduce the sheet resistance of graphene and improved the work function of the device. In particular, the synergistic effect of co-doping with HNO3 helped to improve the number of active sites and charge separation. Along with the increase in carrier concentration, doping with PFSA reduced the number of defects, resulting in the graphene having a smooth and uniform surface, which effectively increased the open-circuit voltage (Voc) from 0.500 to 0.521 V. We surmise that nonvolatile PFSA macromolecular and volatile HNO3 co-doping has high potential for use in the fabrication of low-cost directly grown-graphene-based photovoltaic devices. Highlights Plasma-enhanced chemical vapor deposition technique used for the direct growth of graphene without metal catalyst. Naturally grown oxide thickness optimized. Nonvolatile macromolecular dopant per-fluorinated polymeric sulfonic acid (PFSA) and volatile nitric acid (HNO3) were used for direct growth graphene doping. The power conversion efficiency of ~9.27% with PFSA doping from 7.64%; further, its substantial increase up to 10.44% after co-doping with HNO3 were achieved with long-term stability.

Charge transport in SiCN/Si heterostructures

The steady-state space-charge limited (SCL) current was investigated in amorphous silicon carbonitride (a-SiCN) films deposited on single crystal silicon substrates of p-type conductivity by plasma-enhanced chemical vapor deposition (PECVD) technique. The influence of the deposition time and thermal annealing on the mechanism of the SCL current is studied. It is shown that the SCL current can be limited by shallow or deep traps, depending on the preparation condition. Experimental evidences are obtained that the traps in the films under study are associated with dangling bond defects, presumably due to the decomposition of Si–H bonds. Band and trap parameters (mobility of electrons, density and energy of trap states) are estimated from the SCL current measurements.