Plasma-enhanced Chemical Vapor Deposition Technique Research Articles

Lead-free methyl ammonium tin iodide perovskite thin film growth in single step via plasma enhanced chemical vapour deposition technique and its optoelectronic properties

In the present work, lead free methyl ammonium tin iodide (CH3NH3SnI3 or MASnI3) perovskite thin films have been deposited via single step plasma enhanced chemical vapour deposition (PECVD) technique. In our earlier work, we reported lead based methyl ammonium lead iodide (CH3NH3PbI3 or MAPbI3) perovskite thin film deposition in 2-step, using sputtering technique for the PbI2 thin films and PECVD technique for CH3NH3I (MAI) thin films. CH3NH3I thin films were deposited using PECVD technique in the earlier study. Similarly, CH3NH3SnI3 perovskite thin films are deposited in this work using PECVD technique in single step. Lead is substituted with tin due to its toxic behaviour, environmental and health related issues. CH3NH3SnI3 perovskite is doped n-type via changing the molar ratio of SnI2 and CH3NH3I. SnI2/CH3NH3I ratio is changed from 0.33 to 2 to study the n-type doping of CH3NH3SnI3 perovskite. Deposited CH3NH3SnI3 perovskite thin films are deposited over p-type silicon wafer to make n-type doped n-CH3NH3SnI3/p-Si heterojunction photodiode.

Growth of boron-doped diamond-like carbon films from a low-pressure high-density plasma in inductively coupled chemical vapour deposition

The main objective of this work was the preparation and optimization of boron-doped diamond-like carbon (DLC) films having a good crystalline structure, and electronic and optical properties, at an extremely low deposition pressure and relatively low growth temperature, by varying the flow rates of precursor gases (CH4, B2H6, and Ar) in the plasma controlled at 800 W of RF power. Planar inductively coupled plasma-enhanced chemical vapour deposition technique was used to enable deposition at ∼5.33 Pa and 450 °C, at a constant negative substrate bias of -40 V. The flow rate of the dopant gas (B2H6) was changed to obtain a set of samples, while the precursor gas (CH4) flow rate was kept fixed. The doped sample, prepared with B2H6/CH4 ratio (r) = 1 %, was found to possess a maximum ID/IG (intensity ratio of the D peak with the G peak) of ∼0.819 and a minimum IDia/IG ratio (relative intensity of the Diamond peak to the G peak) of ∼1.149. A high sp3 content of ∼50 % was revealed from the X-ray photoelectron spectroscopy analysis and the transmission electron microscopy images also indicated the presence of prominent 〈111〉, 〈220〉, and 〈311〉 crystallographic planes. The B-doped DLC film possessed enhanced electrical conductivity (σRT) of ∼3.02 ×10−5 S cm−1 relative to the intrinsic DLC films, a corresponding minimum of activation energy (ΔEH) (as calculated in the above room-temperature regime) of ∼170 meV, an optical band gap (Eg) of ∼3.35 eV, and the root mean square roughness of ∼48.12 nm.

Enhanced electromagnetic shielding with ultrathin VGNs-Metal hybrid structures

Designing and preparing lightweight electromagnetic shielding materials at the micron level is crucial for aerospace and military applications. Vertical graphene nanowalls (VGNs) offer high efficiency for electromagnetic shielding due to attributes such as high carrier mobility, porosity, and low density. This study presents the preparation of ultra-thin VGNs/metal stacked films via plasma-enhanced chemical vapor deposition (PECVD) for VGNs, and combined electron beam evaporation (EBE) with cyclic PECVD for metal layers. The PECVD technique ensures homogeneity and controllable thickness of the VGNs. The experimental results demonstrate that the interface between the VGNs and the metal layer exhibits good interfacial contact, resulting in high carrier mobility. Furthermore, incorporating a metal layer with a thickness ratio of 10 % significantly enhances conductivity by an order of magnitude. The hybrid structures exhibit remarkable electromagnetic shielding effectiveness per unit thickness (∼5300 dB mm−1) evaluated in the X-band range (8–12 GHz). Stacked films as thin as 0.01 mm achieve up to 53.4 dB of electromagnetic shielding. Finite element simulations indicate that the presence of opposing electric fields at the graphene-metal interface contributes to higher ohmic loss. The coupling effect at the interface significantly contributes to the material's excellent electromagnetic shielding effectiveness.

Nitrogen admixture effects on growth characteristics and properties of carbon nanowalls

The plasma functionalization of carbon nanowalls (CNWs) is of great interest due to their potential applications in electron field emission and energy storage devices. In this study, the effects of nitrogen on the growth and properties of CNWs are thoroughly investigated by varying a wide range of the N2 concentrations in the CH4/H2/N2 discharge plasma. Nitrogen-doped carbon nanowalls (NCNWs) were synthesized in a single-step growth using the hydrogen radical injection plasma-enhanced chemical vapor deposition technique. The formation of dense NCNWs was found to be enhanced by nitrogen and was three times higher in the sample with a 150 sccm N2 flow rate than in the sample without N2 addition (N-0). As the N2 concentration increased from 0 to 200 sccm, the morphology of CNWs changed from relatively straight to curly-like nanowall structures. A high-resolution optical emission spectroscopic observation shows that as N2 flow increased, CN radicals became the dominant species, suppressing the formation of C2 and CH. Photoelectron spectroscopy analysis revealed the nitrogen doping effect on graphene layers at high N2 concentrations. According to Raman and Transmission Electron Microscopy analyses, the NCNWs had more branched and thicker nanowalls with higher defect concentrations than the N-0 sample. The wettability of NCNWs was improved, particularly for the sample with a N2 flow rate of 150 sccm.

High mobility of IGO/IGZO double-channel thin-film transistors by atomic layer deposition

In this paper, top-gate thin-film transistors (TFTs) of two stacked double-channel layers derived from atomic layer deposition in combination with the plasma-enhanced chemical vapor deposition (PECVD) process were fabricated. The Hall measurement shows that the Hall mobility of the indium gallium oxide (IGO)/indium gallium zinc oxide (IGZO) active layer is 1.6 times more that of the amorphous In-rich IGZO/IGZO layer due to superior carrier percolation conduction paths from the polycrystalline IGO layer. Furthermore, x-ray photoelectron spectroscopy analysis indicates that the IGO/IGZO film has much less oxygen vacancy concentration, which is advantageous in improving not only mobility but also stability. The optimized IGO/IGZO TFT showed both high mobility (38.0 cm2 V−1 s−1) and high stability (ΔVTH = +0.14 V) of a positive bias stress under post-deposition annealing at 250 °C. This strategy provides a feasible process for realizing high-performance TFTs that is compatible with ALD-derived oxides and commercial PECVD techniques in the industry.

High conductivity characteristics of phosphorus-doped nanocrystalline silicon thin films by KrF pulsed excimer laser irradiation method.

The microstructure and high conductivity properties of phosphorus-doped nanocrystalline silicon films were investigated on samples prepared by a plasma-enhanced chemical vapor deposition technique and the KrF pulsed excimer laser irradiation method. The results of Fourier transform infrared spectroscopy and Raman spectroscopy show that Si nanocrystallites with an average diameter of 2 nm to 3 nm are formed in the film. The degree of crystallinity increases with the increase of laser radiation intensity, while the content of hydrogen decreases gradually. More phosphorus atoms are substitutionally incorporated into the nc-Si dots under higher laser irradiation fluence, which is responsible for the high dark conductivity. By controlling the laser fluence at 1.0 J cm-2, the dark conductivity as high as 25.7 S cm-1 can be obtained. Based on the measurements of temperature-dependent conductivity, the carrier transport processes are discussed. The phosphorus doping and the increase of electron concentration are considered to be the reason for high dark conductivity and extremely low conductivity activation energy.

Investigation of the Electronic Properties of Silicon Carbide Films with Varied Si/C Ratios Annealed at Different Temperatures

Hydrogenated amorphous SiC (a-SiC:H) films with various Si/C ratios were prepared using the plasma-enhanced chemical vapor deposition (PECVD) technique. These films were then subjected to thermal annealing at different temperatures to induce crystallization. The electronic properties of the annealed SiC films were investigated through temperature-dependent Hall mobility measurements. It was found that the room-temperature Hall mobilities in the SiC films increased with both the annealing temperature and the Si/C ratio. This increase was attributed to the improved crystallization in the SiC films. Importantly, SiC films with different Si/C ratios annealed at different temperatures exhibited varying temperature dependence behaviors in their Hall mobilities. To understand this behavior, a detailed investigation of the transport processes in SiC films was carried out, with a particular emphasis on the grain boundary scattering mechanisms.

Study on PECVD-hetero-grown β-Ga2O3 thin film and temperature-modulated solar-blind UV photodetection

Using a convenient and low-cost plasma-enhanced chemical vapor deposition technique, uniform Ga2O3 thin films were hetero-grown on c-plane sapphire substrates at different temperatures, with a root mean square roughness as low as 2.71 nm and a growth rate of up to 1121.30 nm h−1; and then the solar-blind UV photodetection performances were discussed in detail. Metal-semiconductor-metal solar-blind UV photodetectors (PDs) based on the five Ga2O3 films prepared at different temperatures exhibit ultra-low dark currents (I dark) ranging among 22–168 fA. Under the illumination of 254 nm UV light, the PD prepared by the film grown at 820 °C possesses the highest performance, with a high photo-to-dark current ratio of 1.47 × 105, a low rise/decay time of 0.067/0.13 s, a specific detectivity (D *) of 3.56 × 1012 Jones, and a linear dynamic range of 92.89 dB. Overall, the results in this work may well provide a referable method for growing cost-effective and ultralow-noise Ga2O3 thin films, as well as achieving decent solar-blind UV sensing applications.

Low-temperature homoepitaxial growth of β-Ga2O3 thin films by atmospheric pressure plasma-enhanced chemical vapor deposition technique

Low-temperature homoepitaxial growth of β-Ga2O3(-201) has been successfully demonstrated by the atmospheric pressure plasma-enhanced chemical vapor deposition technique. To search for low-temperature growth, temperature-dependent studies were carried out between 350 and 600 °C. A high N2 gas flow rate, low gallium source concentration, and high oxygen flow rate ratio played key roles in growing independent and homogeneous multiple nuclei of Ga2O3, leading to three-dimensional grain growth mode, single crystallinity, and the highest growth rate of ⁓0.17 µm/h at 350 °C. The highly reactive atmospheric pressure oxygen plasma actively led to epitaxial growth. The low thermal budget homoepitaxial growth is a record reduction reported thus far.

Simulation and Analysis of Field-dependent Measurements for Different a-Si:H and nc-Si:H Samples

Abstract: A simulation based on the method of weighted residuals is conducted to reproduce the available experimental data of field-dependent steady-state photocarrier grating (SSPG). Different samples of amorphous hydrogenated silicon (a- Si: H) and nanocrystalline hydrogenated silicon (nc- Si: H) thin films prepared by plasma-enhanced chemical vapor deposition (PECVD) technique are employed in the simulation. The reproduced field-dependent data are optimized using 2 indicator. Approximate and correct values of important photoelectronic parameters are extracted from the analysis of results. The analysis reveals values of small-signal response lifetime and electron and hole mobilities comparable to the values obtained from other methods’ applications. The difference between approximate and correct values lies within the experimental error of 5% with one exception regarding a poorly conductive sample. Moreover, the extracted values of both ambipolar diffusion length and charge carrier density are found reasonable and justify the success of the application of the adopted method on the chosen samples. Keywords: Electronic transport phenomena in thin films; Charge carriers: generation, recombination, lifetime, trapping, mean free paths; Photoconduction and photovoltaic effects.

The electronic properties of boron-doped germanium nanocrystals films

Various doping concentrations of boron (B)-doped germanium nanocrystal (Ge NC) films were prepared using the plasma-enhanced chemical vapor deposition (PECVD) technique followed by thermal annealing treatment. The electronic properties of B-doped Ge NCs films combined with the microstructural characterization were investigated. It is worthwhile mentioning that the Hall mobilities {mu }_{mathrm{Hall}} of Ge NCs films were enhanced after B doping and reached to the maximum of 200 cm2 V−1, which could be ascribed to the reduction in surface defects states in the B-doped films. It is also important to highlight that the temperature-dependent mobilities {mu }_{mathrm{H}}(T) exhibited different temperature dependence trends in the Ge NCs films before and after B doping. A comprehensive investigation was conducted to examine the distinct carrier transport properties in B-doped Ge NC films, and a detailed discussion was presented, focusing on the scattering mechanisms involved in the transport process.

Tribocorrosion Susceptibility and Cell Viability Study of 316L Stainless Steel and Ti6Al4V Titanium Alloy with and without DLC Coatings

Stainless steel (SS316L) and titanium alloy (Ti6Al4V) exhibit suitable properties for biomedical applications; however, the tribocorrosion of these materials, which is associated with metallosis, is still a significant concern. This work investigates the effectiveness of DLC smoothing coatings applied to the metals to reduce tribocorrosion and improve cell viability. The study was motivated by many reports of metallosis caused by metal debris in the soft tissues of the body. DLC coatings were produced using the plasma-enhanced chemical vapor deposition (PECVD) technique. The cytotoxicity, genotoxicity, and cell viability of metallic samples with and without DLC coatings were analyzed, considering the chemical composition of the coating and metallic components. The results show that the DLC coatings presented suitable interaction properties and no cytotoxicity or genotoxicity when exposed to the cellular environment, compared with the control group (p < 0.0001). They also demonstrated cell viability, low friction representing a reduction of 80%, and hardness 23–26 GPa, making them ideal for use on fixed implants. It is necessary to control the thickness and roughness of the coating to avoid pinholes and increase the corrosion protection of implants. These DLC coatings with low friction coefficients could facilitate the fixation of implantable pins and screws, including Kirschner wires.

Optimizing the gradient stress sandwich structure thin-film encapsulation for super flexible organic light-emitting devices

To enable organic light-emitting diodes (OLEDs) to be rolled and folded, we need a flexible encapsulation layer that can protect organic materials and metal electrodes that are susceptible to moisture and oxygen. Thin films that encapsulate organic electronic devices need to have excellent mechanical properties to prevent cracks during bending. Using plasma-enhanced chemical vapor deposition (PECVD) and other techniques, we fabricated high-density, stress gradient sandwich-structured films and studied the residual stress of deposited films on encapsulating films and their effect on delamination and cracking. We found that by adjusting the H2/N2 gas ratio and optimizing the Si:N:H ratio of PECVD SiNx:H films, denser, more etch-resistant, higher compressive stress and lower hydrogen content films can be deposited, thereby enable better flexible thin film encapsulation (TFE). We also deposited an inorganic/organic/inorganic sandwich structure film and utilized stress gradient changes to relieve the tensile stress on the outer film during bending. After standardized testing, the OLED with the stress gradient encapsulation structure has no dark spots after bending 10 000 times (bending radius 2 mm). This technique can be used in flexible TFE for various organic devices, showing promising applications in bendable and wearable products.

Methyl ammonium iodide via novel PECVD process for the growth of 2-step vacuum based perovskite (MAPbI3) thin films

MAPbI3 thin films were grown via 2-step vacuum based processes by depositing methyl ammonium iodide (MAI) layer as first step using plasma enhanced chemical vapour deposition (PECVD) technique and then depositing lead iodide (PbI2) layer over it as second step using RF-sputtering technique. To the best of our knowledge MAI layer was deposited for the first time by PECVD technique. MAI solution for PECVD process and PbI2 target for sputtering process were made to deposit these two layers under optimized plasma conditions for the growth of MAPbI3 thin films. Characterization techniques like UV-Vis-NIR spectroscopy and Photoluminescence spectroscopy were performed to study the optical properties. Powder-XRD (PXRD) and glancing incidence XRD (GIXRD) were performed to study structural properties. SEM and cross-SEM were performed for morphological study to view top-view and cross-sectional view of the deposited MAPbI3 perovskite thin film. Perovskite thin films deposited on silicon wafer have been used as perovskite/silicon heterojunction photodiode exhibiting critical performance parameters such as rectifying ratio of 1.58 × 104 at 1.0 V, photo-sensitivity value 7.46 × 102 at light intensity 100 mw/cm2 without biasing.

Microstructure, mechanical, and electrochemical properties of Si/DLC coating deposited on 2024-T3 Al alloy

This work evaluated the microstructure, mechanical, and electrochemical properties of Si/DLC coatings deposited using ‎ the plasma-enhanced chemical vapor deposition (PECVD) technique. Tetramethylsilane and acetylene were used as precursor gases in the deposition process. The characteristics of the coating were estimated using different techniques. The corrosion performance was evaluated using various electrochemical methods in 3.5 wt% NaCl solution. The XPS analysis revealed that the film consists of Si and (a-C: H). The results revealed that as the deposition time increased, the hardness and Young's modulus decreased from 15.83 to 14.21 GPa and 125.8–114.9 GPa, respectively, while the thickness and adhesion strength increased. Moreover, the anti-corrosion ability of the DLC has been improved. It was found the corrosion potential moved to more noble direction (−618 to −562 mVAg/AgCl) while the corrosion rate decreased from 0.012 to 0.001 mmy−1. This trend can be attributed to growing coating thickness and fewer film defects which operated as a protective barrier against the corrosive solution. A failure mechanism of Si/DLC film has been suggested.

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.