Cyclotron Resonance Plasma-enhanced Chemical Vapor Research Articles

Mechanical and optical properties of amorphous silicon nitride-based films prepared by electron cyclotron resonance plasma-enhanced chemical vapor deposition

Silicon nitride (SiNx) based films have been recognized as essential dielectric films in the microelectronics and optoelectronics industry due to their desirable properties, such as high electrical insulation, excellent thermal stability, and compatibility with integrated circuit fabrication processes. They are also a potential candidate for fabricating wavelength-selective reflective coatings and surface passivation layers in building-integrated photovoltaics technologies. SiNx-based films are one of the popular choices for antireflective coatings in photovoltaics as well. Recently, SiNx and oxynitride (SiOyNx) based thin film optical filters have been explored to provide distinct color rendering to solar-charged electrical vehicles. Since solar cells have a lifespan of many years and the coating surfaces are substantial, it is essential to produce films with controlled optical and mechanical properties and maintain mechanical integrity against corrosion and wear. This study aims to design a deposition process and optimize minimal parameters for stable plasma conditions during multilayer deposition of SiNx and SiOyNx films using an electron cyclotron resonance plasma-enhanced chemical vapor deposition reactor with SiH4/N2/O2/Ar precursor mixtures at 120 °C. The primary goal was to investigate the influence of gas flow adjustments on the optical and mechanical properties, specifically targeting the refractive index and mechanical properties of the films. We measured the refractive index and the absorption of the films using variable angle spectroscopic ellipsometry. Then, we evaluated the mechanical residual stress ex situ using the wafer curvature measurement method. We have determined the elastic modulus and the hardness of the films using nanoindentation. The experimental results have shown a significant dependence of the optical and mechanical properties on the deposition parameters. To investigate the factors contributing to the intrinsic mechanical stress and to better understand SiNx film degradation mechanisms, we have studied the effect of postdeposition thermal cycling on the properties of the films. Several thermal-cycling experiments from room temperature to 400 °C were performed on different SiNx films, and the results showed an irreversible variation of the mechanical stress toward the tensile stresses caused by delamination of the films, while the refractive index remained unchanged.

Design and fabrication of color-generating nitride based thin-film optical filters for photovoltaic applications

In this paper, we present the design and fabrication of a 11-layer notch filter for photovoltaic applications. Thickness modulation has been done on a starting quarter-wave design to obtain a 11-layer final structure. For our design parameters, we considered materials with indices of 2.09 and 1.51 as high and low refractive index materials, respectively. Since this filter aims for photovoltaic applications, we defined the substrate as silicon. The design shows a reflection peak of around 73% from 350 to 467 nm with a FWHM of 79 nm along with less than 10% reflection for longer wavelengths of the remaining high transmission region of 300–1200 nm. For fabrication, we used silicon nitride and silicon oxynitride as alternating high and low refractive index materials on a silicon substrate. Layers of silicon nitride and oxynitride were deposited with an electron cyclotron resonance plasma-enhanced chemical vapor deposition reactor and characterized with variable angle spectroscopic ellipsometry and spectrophotometry.

(Student Award, 2nd Place) Optical and Mechanical Properties of Europium-Doped Sicn Thin Films Prepared By Integrated Ecr-PECVD and Magnetron Sputtering

Silicon carbonitride (SiCN) is a wide bandgap semiconductor material that has drawn significant interest over the past few decades due to its excellent optical, electrical, and mechanical properties[1]. Rare earth doping in wide bandgap semiconductors has several prospective applications in the field of photoelectric devices, solid-state lasers, flat panel displays, and high-energy radiation detectors [2]. Among the various rare earth materials, europium (Eu) is particularly interesting due to its optically active divalent and trivalent states capable of emitting in different visible spectral ranges [3].In this work, Eu-doped SiCN thin films were prepared by electron cyclotron resonance plasma-enhanced chemical vapor deposition (ECR-PECVD) with integrated magnetron sputtering [4] on p-type 3” Si (100) substrates. Silane (diluted in 90% argon), nitrogen (diluted in 90% argon) and ethane (C2H6) were used as precursor gases, and a 99.9% pure Eu sputtering target was used as a sputtering source. To understand the effect of C incorporation in the Eu-doped SiCN matrix, we have prepared a set of samples without C. The as-deposited samples were annealed over a wide range of temperatures from 600 to 1100° C in an internet N2 environment. Rutherford backscattering spectrometry (RBS) was performed to determine the atomic concentration of the constituents. Variable angle spectroscopic ellipsometry (VASE) analysis was performed to investigate the optical properties of the films. The room temperature photoluminescence (PL) experiments were carried out with a laser diode excitation source, operating at a wavelength of 375nm. Finally, we performed nanoindentation measurements to understand the deformation behavior of SiCN films as a function of the incorporation of C. The indentation hardness and Young’s modulus of the films were investigated for different Eu and C concentrations.

Optical and Mechanical Properties of Europium-Doped Silicon Oxynitride Thin Films

Light emission from silicon-based systems has gained significant interest over the past few decades with the vision of developing an optoelectronic platform that can be integrated with the existing metal-oxide-semiconductor (MOS) technology [1]. Rare earth doping of silicon-based materials is a promising approach to fabricating efficient light emitting devices because of their excellent luminescence properties and their chemical stability [2]. Europium (Eu) ions are attractive dopants for silicon photonic applications due to their intense emission in the visible spectral region. The efficiency of such photonic devices can be influenced by the mechanical properties of the Eu-doped films. Thus, the integration of these films in photonic devices requires an understanding of their mechanical properties as well. In this work, we discuss the relationship between the photoluminescence (PL) behavior and the elasticity and hardness of Eu doped silicon oxynitride (SiON) thin films.We have fabricated thin films using an electron cyclotron resonance plasma-enhanced chemical vapor deposition system with integrated magnetron sputtering system [3] on p-type 3” Si (100) substrates. Silane (diluted in 90% argon) and nitrogen (diluted in 90% argon) were used as precursor gases, while a 99.9% pure Eu sputtering target was used as a sputtering source. Different sets of samples were fabricated by changing the sputtering power and argon flow rate to understand the effect of deposition parameters on the dopant concentration and the optical and mechanical properties. Post-deposition annealing in nitrogen and a mixture of nitrogen with hydrogen (5%) were performed over a wide range of temperatures from 600° to 1100° C. The effect of hydrogen passivation was studied as well. The atomic concentration of the constituents was identified by Rutherford backscattering spectrometry. Optical properties were investigated by variable angle spectroscopic ellipsometry (VASE) analysis. The PL spectra were obtained at room temperature with a laser diode excitation source, operating at a wavelength of 375nm. Finally, we performed nanoindentation measurements to understand the deformation behavior of SiON films with the incorporation of Eu. The indentation hardness and Young’s modulus of the films were investigated, respectively, for different Eu concentrations and different deposition parameters.Reference[1] A. Moadhen, H. Elhouichet, M. Oueslati, and M. Férid, “Photoluminescence properties of europium-doped porous silicon nanocomposites,” J. Lumin., vol. 99, no. 1, pp. 13–17, 2002, doi: 10.1016/S0022-2313(02)00322-8.[2] Z. Lin R. Huang, H. Wang, Y. Wang, Y. Zhang, Y. Gao, J. Song, C. Song, H. Li, “Dense nanosized europium silicate clusters induced light emission enhancement in Eu-doped silicon oxycarbide films,” J. Alloys Compd., vol. 694, pp. 946–951, 2017, doi: 10.1016/j.jallcom.2016.10.132.[3] J. W. Miller, Z. Khatami, J. Wojcik, J. D. B. Bradley, and P. Mascher, “Integrated ECR-PECVD and magnetron sputtering system for rare-earth-doped Si-based materials,” Surf. Coatings Technol., vol. 336, pp. 99–105, 2018, doi: 10.1016/j.surfcoat.2017.08.051.

Design and Fabrication of Multiple-Color-Generating Thin-Film Optical Filters for Photovoltaic Applications

The use of electric vehicles (EVs) can reduce greenhouse gas emissions, air pollution, dependency on fossil fuels, and their adverse health effects on humans. But, we can only utilize the full environmental benefits of EVs when they are charged with renewable energy sources with zero or low carbon emissions. As a solution, Mobarak et al. [1] suggested integrating low-cost, flexible, and thin-film copper indium gallium selenide (CIGS) solar cells directly onto the steel of all the upward-facing body parts of the vehicles. But, this integration of solar cells comes with an aesthetic drawback. Previously, colorful photovoltaics (PVs) have been designed with one-dimensional (1D) photonic crystals or various 1D and 2D metallic nanostructures for aesthetic building-integrated photovoltaics (BIPVs) [2, 3]. However, the functionality of our application differs from that of BIPV as we need maximum absorption of the solar spectrum to obtain maximum conversion efficiency. Thus, we propose replacing the anti-reflective coating (ARC) present in the solar cells with a notch filter (a narrow high-reflection region in the visible range along with high transmission for the rest of the solar spectrum) to obtain colors.High-performance notch filters with a narrow and ultra-steep notch are well known in literature [4, 5]. Generally, high-performance notch filters are designed with a minimum of 45 layers. It is challenging to use filters with many layers on solar cells due to fabrication and thickness complexities. Thus, we created designs with a maximum of 27 layers for possible integration with photovoltaics. We used OptiLayer [6] to simulate our designs and the gradual evolution technique was used to optimize the designs. We performed our simulations with a multilayer structure of alternating high and low refractive indices of 2.09 and 1.45, respectively, on top of a silicon substrate. We optimized this multilayer structure for three reference wavelengths (400 nm, 550 nm, and 700 nm) resembling three colors. Our designs have notch widths of less than 100 nm for all the reference wavelengths with an average of 70% reflection in the high-reflection region and less than 20% reflection in the high-transmission area.To fabricate our designs, we need materials that are transparent to the solar spectrum targeted by the active material of the solar cells. The materials also need to have refractive indices closer to our simulation. Thus, we chose the combination of silicon nitride and silicon dioxide as our high and low refractive index material, respectively [7, 8]. To better understand our designs’ optical characteristics, we fabricated a scaled-down version of our structure with 5-10 layers. We used electron cyclotron resonance plasma-enhanced chemical vapor deposition (ECR-PECVD) to deposit the multilayer structure on silicon wafers. To obtain the silicon nitride and silicon dioxide layers, we used a SiH4/N2/O2/Ar precursor mixture. By tuning the gas flow rate in the reactor chamber, we tuned the stoichiometry and obtained the required refractive index for each layer. To characterize the refractive index and thickness for each layer, we used variable angle spectroscopic ellipsometry (VASE). We made a detailed comparison of our simulation and fabrication results.

Study on the Performance Impact of Introducing an InN Buffer Layer at Various Deposition Temperatures on InN Film Grown by ECR-PEMOCVD on Free-Standing Diamond Substrate

In this study, InN films are grown at a relatively low temperature by electron cyclotron resonance plasma-enhanced metal organic chemical vapor deposition (ECR-PEMOCVD) on free-standing diamond substrates. Due to the high lattice mismatch rate between InN film and the free-standing diamond substrate, the function of a buffer layer is to build a bridge between the substrate and film to reduce the lattice mismatch between them. Therefore, here, we study the performance impact of introducing an InN buffer layer at various deposition temperatures and explore the optimal buffer layer deposition temperature used to grow relatively high-quality InN films. The experimental results show that when an InN buffer layer is introduced at a deposition temperature of 100 °C, the growth direction of the InN film is perpendicular to the substrate with a high c-axis preferred orientation, the roughness of the surface is minimal, and the particle sizes are consistent with growth in the same direction. Additionally, the carrier mobility is highest, and the carrier concentration is lowest compared with other conditions.

Effect of nitrogen flow on the properties of carbon nitride films deposited by electron cyclotron resonance plasma-enhanced chemical vapor deposition

Amorphous hydrogenated carbon nitride (a-CNx:H) films were fabricated via electron cyclotron resonance microwave plasma-enhanced chemical vapor deposition technology using N2 and C2H2 as nitrogen and carbon sources, respectively. The effects of the N2/C2H2 gas flow ratio on the composition, bond structure, scratch resistance, and optical properties of the a-CNx:H films were investigated. X-ray photoluminescence spectroscopy and Raman spectroscopy results indicated that the N/C atomic ratio, carbon 1s sp3/sp2 ratio, and nitrogen 1s sp3/sp2 ratio increased with increasing N2/C2H2 gas ratio. Pin-on-disk wear tests conducted with a pin made of ultrahigh-molecular weight polyethylene indicated that all the a-CNx:H films exhibited good scratch resistance; however, rubbing with a stainless-steel ball weakened the wear resistance of the a-CNx:H films as the N2/C2H2 gas ratio changed from 5/30 to 30/30. The measured transmittance spectra showed that nitrogen incorporation into the carbon films increased their transmittance in the visible to near-infrared regions. The optical bandgap of the a-CNx:H films was obtained by the Tauc method, which demonstrated that when the N2/C2H2 gas flow ratio changed from 0/30 to 30/30, the optical bandgap increased from 1.18 to 1.86 eV. Our results suggest that a-CNx:H films can be used as optical and protective coatings.

Low-Temperature and Low-Pressure Silicon Nitride Deposition by ECR-PECVD for Optical Waveguides

We report on low-temperature and low-pressure deposition conditions of 140 °C and 1.5 mTorr, respectively, to achieve high-optical quality silicon nitride thin films. We deposit the silicon nitride films using an electron cyclotron resonance plasma-enhanced chemical vapour deposition (ECR-PECVD) chamber with Ar-diluted SiH4, and N2 gas. Variable-angle spectroscopic ellipsometry was used to determine the thickness and refractive index of the silicon nitride films, which ranged from 300 to 650 nm and 1.8 to 2.1 at 638 nm, respectively. We used Rutherford backscattering spectrometry to determine the chemical composition of the films, including oxygen contamination, and elastic recoil detection to characterize the removal of hydrogen after annealing. The as-deposited films are found to have variable relative silicon and nitrogen compositions with significant oxygen content and hydrogen incorporation of 10–20 and 17–21%, respectively. Atomic force microscopy measurements show a decrease in root mean square roughness after annealing for a variety of films. Prism coupling measurements show losses as low as 1.3, 0.3 and 1.5 ± 0.1 dB/cm at 638, 980 and 1550 nm, respectively, without the need for post-process annealing. Based on this study, we find that the as-deposited ECR-PECVD SiOxNy:Hz films have a suitable thickness, refractive index and optical loss for their use in visible and near-infrared integrated photonic devices.

Impact of the Deposition Temperature on the Structural and Electrical Properties of InN Films Grown on Self-Standing Diamond Substrates by Low-Temperature ECR-MOCVD

The progress of InN semiconductors is still in its infancy compared to GaN-based devices and materials. Herein, InN thin films were grown on self-standing diamond substrates using low-temperature electron cyclotron resonance plasma-enhanced metal organic chemical vapor deposition (ECR-PEMOCVD) with inert N2 used as a nitrogen source. The thermal conductivity of diamond substrates makes the as-grown InN films especially attractive for various optoelectronic applications. Structural and electrical properties which depend on deposition temperature were systematically investigated by reflection high-energy electron diffraction (RHEED), X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and Hall effect measurement. The results indicated that the quality and properties of InN films were significantly influenced by the deposition temperature, and InN films with highly c-axis preferential orientation and surface morphology were obtained at optimized temperatures of 400 °C. Moreover, their electrical properties with deposition temperature were studied, and their tendency was correlated with the dependence on micro- structure and morphology.

Study on Preparation and Properties of InN Films on Self-Supporting Diamond Substrates Under Different Nitrogen Flows

Several InN film samples with superb properties were prepared on a self-supporting diamond substrate for different nitrogen flow rates using an electron cyclotron resonance plasma-enhanced metal-organic chemical vapor deposition (ECR-PEMOCVD) system. After the InN film samples were obtained, the samples were characterized via reflected high-energy electron diffraction (RHEED), X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscope (AFM), and electron probe micro-analysis (EPMA) to study the effect of the nitrogen flow on the quality of the InN films. The experimental results show that the variation in the nitrogen flow has a great impact on the preferential growth of the (0002) crystal plane of the InN thin-film. By increasing the nitrogen flow moderately, the crystal quality of the film is improved. Under the growth condition of appropriate nitrogen flow, InN thin-films with a preferred orientation along the c-axis can be obtained, and the surface of the resulting InN thin-films is relatively flat. However, a high nitrogen flow does not improve the film crystal quality. The results of the experiment and of the analysis show that the InN films prepared with a nitrogen flow rate of 80 sccm have an excellent preferential orientation. The result of the EPMA test shows that the percentages of the In and N atoms in the prepared film samples are close to a ratio of 1:1, and a small amount of metal In droplets is present. In addition, the InN thin-films prepared in such condition have an excellent surface morphology and composition.

X-ray Absorption Spectroscopy of Silicon Carbide Thin Films Improved by Nitrogen for All-Silicon Solar Cells

Synchrotron-based experiments in combination with optical measurements were used to explore the potential of a photovoltaic material based on silicon carbonitride (SiCN) thin films, in particular for the use in space solar cells. The large bandgap, SiCN films were fabricated using electron cyclotron resonance plasma-enhanced chemical vapour deposition (ECR-PECVD) followed by low-temperature annealing processes. X-ray absorption near edge structure (XANES) with excitations at the carbon, nitrogen, and silicon K-edges verifies that the presence of nitrogen tends to disrupt Si–C networks. This results in the enhancement of light absorption and bandgap widening, which is desirable for front emitters in all-silicon tandem solar cells. The ternary structure of SiCN allows bandgap engineering and tuning of the light absorption and refractive index through careful design of the composition. XANES showed that the thermal annealing at a medium temperature (500 °C) using N2 ambient promoted the formation of Si–Si and C–N sp2 bonds before disappearing in higher annealing temperatures. In our opinion unlocking the potential of robust SiC mixed with nitrogen in SiCN matrix has appeal in radiation-resistant solar cells, where it can serve as the top emitter layer in all-silicon tandem solar cells and at the same time benefits the antireflection properties.

Annealing of silicon carbonitride nanostructured thin films: interdependency of hydrogen content, optical, and structural properties

Silicon carbonitride (SiCxNy) materials, inspired by their outstanding multifunctional properties, are finding increasing applications in a variety of fields, including as next generation solar cells and hard coatings. Hydrogenated SiCxNy thin films, along with binary submatrices of stoichiometric SiC and SiN3 as a reference, were deposited using electron cyclotron resonance plasma-enhanced chemical vapor deposition. We described a comparative study of the effects of post-deposition thermal annealing, from 300 to 1200 °C, on the evolution of hydrogen-rich a-SiC1.2N0.7:H1.4 thin films. Concurrently, two featured annealing temperatures (500 and 900 °C) were found to have the significant influence on the morphology, optical, and microstructural properties of the films. During annealing the amorphous phase of SiC1.2N0.7:H1.4 thin films was fully maintained according to the transmission electron microscopy and X-ray diffraction analyses. The hydrogen density was quantitatively analyzed employing two different experimental techniques, elastic recoil detection and Fourier transform infrared spectroscopy, showing the associate annealing temperatures of hydrogen desorption, breaking of all hydrogen-terminated bonds, and depletion of all hydrogen content. The refractive indices and optical band gap of the films were calculated using variable angle spectroscopic ellipsometer. Thermal annealing resulted in hydrogen desorption and consequently layer densification along with an increase in the refractive index. During the annealing process, first the optical band gap widened, and then narrowed due to hydrogen out-diffusion or chemical bond restructuring, depending on the annealing temperature. In addition, Rutherford backscattering spectrometry and X-ray photoelectron spectroscopy were performed. These findings are discussed in the context of the interdependency of the hydrogen desorption and thermally induced changes in chemical bonds, mass density, and optical properties.

Effect of Temperature on the Microstructure and Electrical Conductivity of Microcrystalline Si Films

Micro-Si films were deposited using Ar diluted SiH4 gaseous mixture by electron cyclotron resonance plasma-enhanced chemical vapor deposition (ECR-PECVD). The effects of the substrate temperature on microstructure and electrical conductivity of micro-Si film were investigated. The results show that, with the increasing of substrate temperature, crystallinity and grain size increased monotonously, of which a competing balance would determine the electrical conductivity of micro-Si films. Based on these results, relatively small grain size and appropriate crystallinity would be beneficial to improve the electrical properties of micro-Si films.

Electron affinity of cubic boron nitride terminated with vanadium oxide

A thermally stable negative electron affinity (NEA) for a cubic boron nitride (c-BN) surface with vanadium-oxide-termination is achieved, and its electronic structure was analyzed with in-situ photoelectron spectroscopy. The c-BN films were prepared by electron cyclotron resonance plasma-enhanced chemical vapor deposition employing BF3 and N2 as precursors. Vanadium layers of ∼0.1 and 0.5 nm thickness were deposited on the c-BN surface in an electron beam deposition system. Oxidation of the metal layer was achieved by an oxygen plasma treatment. After 650 °C thermal annealing, the vanadium oxide on the c-BN surface was determined to be VO2, and the surfaces were found to be thermally stable, exhibiting an NEA. In comparison, the oxygen-terminated c-BN surface, where B2O3 was detected, showed a positive electron affinity of ∼1.2 eV. The B2O3 evidently acts as a negatively charged layer introducing a surface dipole directed into the c-BN. Through the interaction of VO2 with the B2O3 layer, a B-O-V layer structure would contribute a dipole between the O and V layers with the positive side facing vacuum. The lower enthalpy of formation for B2O3 is favorable for the formation of the B-O-V layer structure, which provides a thermally stable surface dipole and an NEA surface.

Influence of Power on the Microstructure and Optical Properties of Microcrystalline Si Films

Microcrystalline silicon films were deposited using Ar diluted SiH4 gaseous mixture by electron cyclotron resonance plasma-enhanced chemical vapor deposition (ECR-PECVD). The effects of power on microstrcture and optical properties of microcrystalline silicon films were investigated. The results show that, with the increasing of the power, the crystallinity increased, but the concentration of hydrogen decreased monotonously. Furthermore, the absorption coefficient of the films increased monotonously, and the optical bandgap changed from 1.89eV to 1.75eV with the microwave power ranging from 400 W to 650W.

Reusable thin film photocatalyst of Fe-doped TiO2deposited by ECR plasma

The paper presents an improved method of depositing nanocrystalline thin films of Fe-doped TiO2 to be used as a reusable cyclic photocatalyst for degrading the organic pollutants. The technique of electron cyclotron resonance plasma-enhanced chemical vapor deposition was employed with titanium tetra-isopropoxide (C12H28O4Ti) and ferrocene (C10H10Fe) as precursors of Ti and Fe, respectively. Optical emission spectroscopy was used to identify the reactive species, to determine the electron temperature and the ion density during deposition. The films were characterized using optical absorption and photoluminescence spectra, whereas the morphological analysis was carried out with scanning electron microscopy. Strong adhesion of the deposited films with the substrate ruled out any possibility of TiO2 particles being leached out. It was confirmed by observing the degradation rate of the same film repeatedly. Cyclic use of the film for the catalytic reactions thus makes the process much user friendly for the water treatment. Copyright © 2014 John Wiley & Sons, Ltd.

Substrate Dependence of Microcrystalline Silicon Growth with SiH<sub>4</sub> Diluted by Ar

Microcrystalline Si films were deposited by electron cyclotron resonance plasma-enhanced chemical vapor deposition (ECR-PECVD) using Ar diluted SiH4gaseous mixture. The effects of the substrate on deposition rate, preferred orientation and roughness of the films were investigated. The results show that, the influence of the substrate surface chemical nature on the deposition rate is significant in the initial stage of the growth. And considering the crystallinity and roughness of the films, the substrate is favored in its preferred orientation with a rougher surface. Based on these results, it is confirmed that the combination of diffusion and etching is indispensable to describe the deposition of μc-Si with SiH4diluted by Ar, and the mechanism of μc-Si growth could be controlled by diffusion of Si and etching of the Ar+on the film surface.

Low-temperature ECR-PEMOCVD deposition of high-quality crystalline gallium nitride films: A comparative study of intermediate layers for growth on amorphous glass substrates

A low temperature growth method based on an electron cyclotron resonance plasma-enhanced metal organic chemical vapor deposition system (ECR-PEMOCVD) was proposed for the growth of GaN (Gallium nitride) films on ordinary amorphous soda-lime glass substrates. To alleviate the large lattice mismatch between GaN film and glass substrate and improve the heat dissipation performance for potential optoelctrical device application, five intermediate layers (Cu, Ni, Ti, Ag, and ITO) were deposited on the glass substrate before the growth of GaN. A comparative study was performed through structural analysis of the as-grown GaN films with various intermediate layers investigated by means of in-situ reflection high energy electron diffraction (RHEED), X-ray diffraction (XRD), and atomic force microscopy (AFM). The results indicate that the Ti intermediate layer has a great advantage over other intermediate layers in view of crystalline quality and smooth surface, therefore is more suitable and preferred for the potential application in optoelectronic devices.

Excitation mechanism and thermal emission quenching of Tb ions in silicon rich silicon oxide thin films grown by plasma-enhanced chemical vapour deposition—Do we need silicon nanoclusters?

In this work, we will discuss the excitation and emission properties of Tb ions in a Silicon Rich Silicon Oxide (SRSO) matrix obtained at different technological conditions. By means of electron cyclotron resonance plasma-enhanced chemical vapour deposition, undoped and doped SRSO films have been obtained with different Si content (33, 35, 39, 50 at. %) and were annealed at different temperatures (600, 900, 1100 °C). The samples were characterized optically and structurally using photoluminescence (PL), PL excitation, time resolved PL, absorption, cathodoluminescence, temperature dependent PL, Rutherford backscattering spectrometry, Fourier transform infrared spectroscopy and positron annihilation lifetime spectroscopy. Based on the obtained results, we discuss how the matrix modifications influence excitation and emission properties of Tb ions.

Influence of Nitridation Time on the Characteristics of GaN Films Deposited on Ni Metal Substrate by ECR-MOCVD

GaN films were deposited on metal Ni substrates using electron cyclotron resonance plasma-enhanced metal organic chemical vapour deposition system (ECR-PEMOCVD). The nitridation time dependent structural and morphological characteristics of GaN films were systematically investigated by reflection high energy electron diffraction (RHEED), X-ray diffraction (XRD), and scanning electron microscope (SEM) analysis. The results indicate that it is feasible to deposit GaN films on Ni metal substrate under the proper deposition procedures. The high quality GaN films with c-axis preferred orientation and dense and uniform microstructure are successfully obtained under the optimized nitridation time. The GaN/Ni structure has great potential for the improvement of short-wavelength optical devices with excellent heat dissipation.