Pressure Chemical Vapor Deposition Technique Research Articles

Modulation of the morphological and optical properties of CVD grown non-Stochiometric [formula omitted] nanostructures by various substrate angles

Gallium oxide (Ga2O3) nanostructures (NSs) were synthesized via atmospheric pressure chemical vapor deposition (APCVD) technique assisted by hydrogen. The geometrical orientation in terms of the substrate angle was studied to investigate its influence on the morphological, compositional and optical properties of the material. The results revealed that the geometry, stoichiometry and optical parameters of Ga2O3 could be tuned by substrate angle variations during deposition. Tilting the substrate was found to enhance the step coverage of the substrate and the Ga/O atomic ratio above the stoichiometric value. Bandgap of the films was observed to vary inversely (ranged between 4.590 and 4.664eV) to the Ga/O atomic ratio. The refractive index at wavelength of 632.8 nm, dispersion and single oscillator energy of the prepared films were also evaluated, and were found to be in the range of 2.129–3.265, 20.952–56.520eV and 5.309–6.387eV, respectively, with the increase of substrate angle.

High-performance GeSi/Ge multi-quantum well photodetector on a Ge-buffered Si substrate.

This work demonstrates a high-performance photodetector with a 4-cycle Ge0.86Si0.14/Ge multi-quantum well (MQW) structure grown by reduced pressure chemical vapor deposition techniques on a Ge-buffered Si (100) substrate. At -1 V bias, the dark current density of the fabricated PIN mesa devices is as low as 3 mA/cm2, and the optical responsivities are 0.51 and 0.17 A/W at 1310 and 1550 nm, respectively, corresponding to the cutoff wavelength of 1620 nm. At the same time, the device has good high-power performance and continuous repeatable light response. On the other hand, the temperature coefficient of resistance (TCR) of the device is as high as -5.18%/K, surpassing all commercial thermal detectors. These results indicate that the CMOS-compatible and low-cost Ge0.86Si0.14/Ge multilayer structure is promising for short-wave infrared and uncooled infrared imaging.

Modification of the Physical Properties of SnO2 Thin Films for Optoelectronic Applications Combining Rapid Atmospheric Pressure Chemical Vapor Deposition Technique and Heat Treatment

Herein, the influence of the postannealing process on tin oxide thin films deposited by chemical vapor deposition in the atmospheric pressure technique is investigated. The as‐deposited films are heat treated under different environments, including ambient air, oxygen, nitrogen, and vacuum. The postannealing process is performed at 600 ºC for 60 min. It is worth mentioning that no sign of damage or destruction has been observed in samples after the annealing process. The structural characterization of the thin films is studied using X‐ray diffraction analysis, which reveals an increase in the peak intensities after annealing. Field‐emission scanning electron microscope surface morphology shows that heat‐treated tin oxide thin films have larger grain sizes than as‐deposited ones. Hall effect analysis shows a significant reduction in sheet resistance and a substantial increase in mobility after postannealing. The ultraviolet–visible–near‐infrared transmittance spectra in the 300–3000 nm range exhibit near 80% transparency in the visible region after annealing. Furthermore, the estimated bandgap values increase from 2.95 to 3.08 eV as the carrier concentration increases after the heat treatment. The results suggest the superiority of the oxygen‐annealed sample over the other annealing environments.

A temperature-based synthesis and characterization study of aluminum-incorporated diamond-like carbon thin films

The present work deals with the study of various properties of aluminum (Al)-incorporated diamond-like carbon (DLC) thin films synthesized using the atmospheric pressure chemical vapor deposition (APCVD) technique by varying the deposition temperature (Td) and keeping the N2 flow rate constant. Surface morphology analysis, resistance to corrosion, nanohardness (H), and Young’s modulus (E) of the coatings were carried out using atomic force microscopy (AFM), corrosion test, scanning electron microscopy (SEM), and nanoindentation test, respectively. SEM results showed a smoother surface morphology of the coatings grown at different process temperatures. With an increase in process temperature, the coating roughness (Ra) lies in the range of 20–36 µm. The corrosion resistance of the coating was found to be reduced with a consecutive increase in the deposition temperature from 800℃ to 880℃. However, above 880℃, the resistance increases further, and it may be due to the presence of more Al weight percentage in the coating. The nanoindentation result revealed that H and E of the coating increase with an increase in the CVD process temperature. The elastic–plastic property indicated by H/E and H3/E2, which are also indicators of the wear properties of the coating, were studied using the nanoindentation technique. The residual stresses (σ) calculated using Stoney’s equation revealed a reduction in residual stress with an increase in the process temperature.

Influence of Deposition Time on Titanium Nitride (TiN) Thin Film Coating Synthesis Using Chemical Vapour Deposition

Titanium nitride (TiN) thin film coatings were grown over silicon (p-type) substrate using the atmospheric pressure chemical vapour deposition (APCVD) technique. The synthesis process was carried out to evaluate the effect of deposition time on the physical and mechanical characteristics of TiN coating. Thin films grown over Si substrate were further characterised to evaluate the morphological properties, surface roughness and mechanical properties using a scanning electrode microscope (SEM), atomic force microscopy (AFM) and nanoindentation, respectively. EDS equipped with SEM showed the presence of Ti and N elements in considerable amounts. TiN morphology obtained from the SEM test showed small-sized particles on the surface along with cracks and pores. AFM results revealed that by increasing the deposition time, the surface roughness of the coating also increased. The nanomechanical properties such as nanohardness (H) and Young’s modulus (E), etc., evaluated using the nanoindentation technique showed that higher deposition time led to an increase in H and E. Overall, it was observed that deposition time plays a vital role in the TiN coating deposition using the CVD technique.

Study of morphological evolution and growth mechanism of CVD grown 2D tin disulfide

Fractal patterns formed during non-equilibrium growth processes and are abundant in nature. However, the mechanism of their formation remains unknown. Several growth factors such as relaxation rate, cooling rate, diffusion anisotropy and growth time were identified for regulating the fractal growth. Nevertheless, most articles focused on regular shaped (such as triangles and hexagons) 2D layered metal dichalcogenides (LMDs), whereas fractals have received less attention. Therefore, understanding the controlled synthesis of LMDs materials with unique edge structures is highly desired for various potential applications. Here, we report large fractal growth of tin disulfide (SnS2) by atmospheric pressure chemical vapor deposition technique. The edge length of the atomically thin SnS2 fractals range from 5 to 100 µm. Our study shows the morphological evolution from fractal to triangular-like structure during the CVD growth process. To understand this phenomenon, we anticipated that the early phase of the growth mostly occurs via kinetic regulated pathway resulting fractal like structure. As the domains go through numerous relaxation phases throughout the edge diffusion process, the morphology gets more compact or regular, indicating increased thermodynamic control over the growth process. We have also provided a physical model for the growth mechanism of CVD grown SnS2.

Low temperature chemical vapor deposition as a sustainable method to obtain c-oriented and highly UV luminescent ZnO thin films

We report the fabrication of c-oriented and transparent ZnO films with high UV/visible luminescent ratio on glass substrates using a very simple low temperature-atmospheric pressure chemical vapor deposition technique, where zinc acetate (ZA) and water vapor were the precursors. Both the ZA source and the glass substrate are in a same work temperature zone (240 °C) and no vacuum system is necessary. Highly c-oriented ZnO films were obtained with different growth rates (∼2 to 44 nm/min) by varying the source-substrate distance. The samples were characterized by scanning electron microscopy, X-ray diffraction and UV–vis, photoluminescence (PL) and energy-dispersive X-ray spectroscopies. Films grown with the highest growth rate exhibited narrower bandgap, which is correlated with a violet component in the PL spectra.

Spectroscopic Study of the 3107 cm−1 and 3143 cm−1 H-Related Defects in Type Ib Diamonds

Hydrogen-related infrared absorption bands in natural diamonds have been extensively investigated and widely used to identify natural, treated, and synthetic diamonds grown by high pressure and high temperature (HPHT) and chemical vapor deposition (CVD) techniques. However, the evolutional behavior of the hydrogen-related defects and the relationship between the hydrogen-related and nitrogen-related defects in natural and HPHT-treated Ib diamonds are unclear. In this article, the hydrogen-related defects, particularly the infrared absorption bands of 3107 cm−1 and 3143 cm−1 in natural type Ib diamonds and HPHT-treated natural diamonds, were systematically investigated using spectroscopic techniques. It was found that the 1405 cm−1 absorption intensity was directly proportional to the 3107 cm−1 absorption intensity; the 3143 cm−1 absorption intensity increased with the increase in the 3107 cm−1 absorption intensity, but there was no strict linear relationship between them. The 3143 cm−1 band was not only related to the intensity of the 3107 cm−1 but also related to the value of NC/NA in natural diamonds. When the value of NC/NA was less than one, the 3143 cm−1 band was more pronounced. After high-temperature annealing, the absorption intensities of the 3107 cm−1 and 3143 cm−1 in natural type Ib diamonds became stronger. However, in HPHT synthetic diamonds, only a 3107 cm−1 defect was introduced with the increase in the A centers in the diamonds. The difference and the detectability of the 3143 cm−1 and 3107 cm−1 bands investigated could be efficiently used to identify natural type Ib diamonds from their counterparts, including the synthetic diamonds and the HPHT-treated diamonds.

Decoupling trade-off thermoelectric relations and controlled out-plane lattice dynamics in few-layer MoS2

We report on the thermoelectric properties of few-layer MoS2 fabricated on 290 nm-SiO2/Si by a two-zone atmospheric pressure chemical vapor deposition (CVD) technique. The decoupling of electrical conductivity and Seebeck coefficient is noticed after 592 K, where the electrical conductivity (σ) is linearly increased and the Seebeck coefficient (S) is exponentially increased. The highest values of σ and S are 10.9 S cm−1 and 10312 nV K−1 at 734 K, respectively, and the highest power factor (S2σ) is 116 nW m−1 K−2 at 734 K. The calculated out-plane (A1g) displacement and the decreased A1g phonon lifetime are revealing the reduced phonon transport. The current investigations paved an attention to decouple the thermoelectric properties of few layer MoS2.

Synthesis of SiC films by Atmospheric Pressure Chemical Vapor Deposition using Dimethylisopropylsilane Polymeric Precursor

Abstract: Silicon carbide (SiC) thin films were deposited on Quartz, SiC, and GaAs substrates under a hydrogen (H2) ambient at 850°C using dimethylisopropylsilane [CH(CH3)2SiH(CH3)2] as a single molecular polymeric precursor by the atmospheric pressure chemical vapor deposition (APCVD) technique. Effects on the SiC films from variation of precursor to H2 flow ratio in the reactive chamber as well as those which resulted when vacuum or positive pressures are utilized during temperature ramping have been investigated. Detailed analysis of Fourier Transform Infrared Spectroscopy (FTIR) results indicate the formation of SiC at 850°C in accordance with residual Si-CH2, Si-CH3 and Si-O bonds. Confirmed by either X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) or Energy Dispersive Spectroscopy (EDS), results show that the produced SiC films are dense, rough surfaced, void-free, and consist of a crystalline core showing the presence of beta-SiC and small amounts of alphaSiC. Pre-experimental thermodynamic modeling provided the valuable insight that an increase of the precursor to direct H2 flow ratio would provide a decrease of unreacted carbon in the SiC matrix yielding higher quality SiC films. These simulations also have shown reasonable agreement with our experimental observations. Keywords: SiC thin Film, Polymeric Precursor, Chemical Vapor Deposition, Thermodynamic Modelling

Performance of High Efficiency Avalanche Poly-SiGe Devices for Photo-Sensing Applications.

This paper explores poly-silicon-germanium (poly-SiGe) avalanche photo-sensors (APSs) involving a device of heterojunction structures. A low pressure chemical vapor deposition (LPCVD) technique was used to deposit epitaxial poly-SiGe thin films. The thin films were subjected to annealing after the deposition. Our research shows that the most optimal thin films can be obtained at 800 °C for 30 min annealing in the hydrogen atmosphere. Under a 3-μW/cm2 incident light (with a wavelength of 550 nm) and up to 27-V biased voltage, the APS with a n+-n-p-p+ alloy/SiO2/Si-substrate structure using the better annealed poly-SiGe film process showed improved performance by nearly 70%, 96% in responsivity, and 85% in quantum efficiency, when compared to the non-annealed APS. The optimal avalanche multiplication factor curve of the APS developed under the exponent of n = 3 condition can be improved with an increase in uniformity corresponding to the APS-junction voltage. This finding is promising and can be adopted in future photo-sensing and optical communication applications.

Low doping in-situ strategy leading to polysilicon based TFTs exhibiting high stability under stress effects and enhanced electrical performances

In the present work, we investigate the effect of low phosphorus doped polysilicon thin films. These later are deposited on glass substrates by low pressure chemical vapor Deposition (LPCVD) technique and are in situ doped with phosphine adjunction to silane. Doping levels are reported by the phosphine to silane ratio Γ varying from 0 (undoped layer) to heavily doped layer almost 1.2 × 10–3. Films are characterized by different techniques as Photothermal Deflection Spectroscopy (PDS), photoluminescence measurements and x-ray diffraction of polycrystalline layers. The last one reveals that doping concentration giving modification in crystallite size and presence of microstrain, so a clear reduction in the Eg value was observed for the slightest doped layer (Γ = 3.7 × 10–7) by comparaison with the undoped one ((Γ = 0). Results give evidence of an optimum doping level to obtain higher polysilicon films quality. Polysilicon film quality has been correlated to phosphorus doping levels. Thin film transistors (TFTs) are fabricated on glass substrate using a top gate four mask process at low temperature (<600 °C). Electrical characterizations highlight significant improvements in the TFTs performances using slightly doped film instead of undoped one as active layer. Based on Levinson’s model, density of states within the grain boundaries is also found to be the lowest. Stability under stress is enhanced too. For slightly doped films, electrical characterizations indicate that both threshold voltage and density of states NT within the grain boundaries have their lowest values. Although, the field effect mobility μ records its highest values. Additionally, low doping levels enhances the TFT stability under stress. As a result, the in situ low doping strategy opens the way to manufacture polysilicon electronic devices exhibiting high electrical performances and a rather high stability under stress effects.

Nonlinear Optical Properties of ZnO Thin Film at Low Laser Intensity Using Z-Scan Technique

In this work, a highly sensitive well-known z-scan technique was employed to study the nonlinear optical properties of Zinc Oxide thin films as a function of low laser fluencies. The transmissions of the continues-wave red laser diode with wavelength of (650 nm) were measured from the ZnO thin film sample with thickness of (425 nm). The thin film used in this study was deposited on the glass substrates based on atmospheric pressure chemical vapor deposition (APCVD) technique. The measurements were obtained at low laser powers ranging from (1.9-2.5) mW. The results indicated that the nonlinear absorption coefficient, refractive index and the third-order nonlinear optical susceptibility increase with increasing the laser intensity. The obtained curves of the closed aperture showed a positive sign of the nonlinear refractive index which in turn attributed to the self-defocusing of the material. The optical parameters obtained in this work are relatively comparable with that obtained elsewhere. The results also confirm the reliability of the z-scan approach even at low laser intensities.

Temperature dependence of β-Ga2O3 heteroepitaxy on c-plane sapphire using low pressure chemical vapor deposition

β-Ga2O3 has drawn significant attention for power electronics and deep ultraviolet (UV) photodetector applications owing to its wide bandgap of ~4.4–4.9 eV and high electric breakdown strength of ~7–8 MV/cm. Growth of β-Ga2O3 epitaxial thin films with high growth rate has been recently reported using low pressure chemical vapor deposition (LPCVD) technique. In this work, we have investigated the effect of growth temperature on β-Ga2O3 films grown on c-plane sapphire substrates using LPCVD. We performed growths by varying temperatures from 800 °C to 950 °C while keeping all other growth parameters (Ar/O2 gas flow rates, growth pressure, and Gallium precursor to substrate distance) constant. Optical, structural, and surface characterizations are performed to determine the thickness, bandgap, phase purity, crystal orientation, and crystalline quality of the grown thin films. Amorphous islands of Ga2O3 are observed at growth temperature of 800 °C while continuous and crystalline (−201) oriented β-Ga2O3 thin films are achieved for growth temperatures of 850–950 °C. Crystallinity of the films is found to improve with increase in growth temperature with a minimum rocking full width at half maximum of 1.52º in sample grown at 925 °C. For all the samples grown at and above 875 °C, transmittance measurements revealed an optical bandgap of ~4.77–4.80 eV with high growth rate of ~6 µm/h.

Atmospheric pressure chemical vapor deposition of indium oxide nanostructured films for photoelectrochemical application

In this work, indium oxide nanostructured films were synthesized by hydrogen assisted atmospheric pressure chemical vapor deposition technique at various deposition temperatures. The surface morphology, crystallinity, and optical properties of the synthesized films were investigated by field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), and UV–vis-NIR measurement, respectively. Photoelectrochemical (PEC) activity of the fabricated films was investigated in a 0.5 M aqueous solution of KOH under simulated solar illumination (150 W Xenon arc lamp). The result of the indium oxide photoanodes' PEC performance shows that the sample grown at 950°C exhibited optimal performance. It generates an overall photocurrent density of 2.56 mA/cm2, with an incident photon to current conversion efficiency (IPCE) of 37% around λ=390 nm of the incident spectrum. The sample also recorded a significant applied bias to photon conversion efficiency (ABPE) of 0.60%. The superiority of the PEC performance of the sample could be attributed to the film composition, crystallinity and bandgap reduction, as well as low flat band potential and enhanced charge carrier density.

Effect of nitrogen (N2) flow rate over the tribological, structural and mechanical properties diamond-like carbon (DLC) thin film

In this article, nitrogen (N2) doped diamond-like carbon (N-DLC) coatings are deposited by Atmospheric pressure chemical vapor deposition (APCVD) technique at varying N2 flow rates and are investigated by scanning electron microscopy (SEM), atomic force microscopy (AFM), Raman spectroscopy, nanoindentation (NI) and nano scratch (NS) characterization. The wear rate (WR) and coefficient of friction (μ) of the N-DLC thin films increase from 1.32 × 10−4 to 3.11 × 10−4 μm2 and 0.05 to 0.15 with the increase of load from 40 to 70 mN at 70 sccm N2 flow rate. The results showed that there is a significant improvement in the tribological and mechanical properties of the APCVD synthesized DLC film as compare to the other PVD deposited DLC film.

Comparison of passivation properties of plasma-assisted ALD and APCVD deposited Al2O3 with SiNx capping

In this paper, we report on the direct comparison of Al2O3 films deposited by plasma-assisted atomic layer deposition (ALD) and atmospheric pressure chemical vapor deposition (APCVD) techniques on the passivation properties of both bare and boron diffused Si surfaces. It is found that ALD and APCVD deposited Al2O3 layers with SiNx capping have very similar chemical composition, hydrogen concentration at the Al2O3/Si interface, and interface defect density (Dit), but the ALD film has slightly higher negative fixed charge (Qf) after a high temperature (~750 °C) contact firing cycle typically used for solar cell fabrication. Both films showed excellent surface recombination velocities of <5 cm/s on planar and textured un-diffused Si wafers, but the ALD films gave 1 to 8 fA/cm2 lower emitter saturation current densities (J0e) on implanted boron emitters with sheet resistance in the range of 90–180 Ω/□. This is attributed to the observed slightly higher negative charge-induced field-effect passivation in the ALD films. However, SiNx/Al2O3/p+/n/n+ passivated emitter rear totally diffused (PERT) cell structures fabricated with 110 and 150 Ω/□ emitter in this study showed no appreciable difference in cell efficiency. Device analysis and simulations showed that even for >23% high-performance solar cells design, with very low bulk and rear contact recombination, the observed small difference in J0e has negligible effect on cell efficiency. Thus, APCVD Al2O3 passivation of B emitter can produce comparable efficiencies to their counterpart ALD Al2O3 passivated n-type Si solar cells.

Strained Si0.2Ge0.8/Ge multilayer Stacks Epitaxially Grown on a Low-/high-Temperature Ge Buffer Layer and Selective Wet-Etching of Germanium.

With the development of new designs and materials for nano-scale transistors, vertical Gate-All-Around Field Effect Transistors (vGAAFETs) with germanium as channel materials have emerged as excellent choices. The driving forces for this choice are the full control of the short channel effect and the high carrier mobility in the channel region. In this work, a novel process to form the structure for a VGAA transistor with a Ge channel is presented. The structure consists of multilayers of Si0.2Ge0.8/Ge grown on a Ge buffer layer grown by the reduced pressure chemical vapor deposition technique. The Ge buffer layer growth consists of low-temperature growth at 400 °C and high-temperature growth at 650 °C. The impact of the epitaxial quality of the Ge buffer on the defect density in the Si0.2Ge0.8/Ge stack has been studied. In this part, different thicknesses (0.6, 1.2 and 2.0 µm) of the Ge buffer on the quality of the Si0.2Ge0.8/Ge stack structure have been investigated. The thicker Ge buffer layer can improve surface roughness. A high-quality and atomically smooth surface with RMS 0.73 nm of the Si0.2Ge0.8/Ge stack structure can be successfully realized on the 1.2 µm Ge buffer layer. After the epitaxy step, the multilayer is vertically dry-etched to form a fin where the Ge channel is selectively released to SiGe by using wet-etching in HNO3 and H2O2 solution at room temperature. It has been found that the solution concentration has a great effect on the etch rate. The relative etching depth of Ge is linearly dependent on the etching time in H2O2 solution. The results of this study emphasize the selective etching of germanium and provide the experimental basis for the release of germanium channels in the future.

Strain relaxation in different shapes of single crystal graphene grown by chemical vapor deposition on copper

The chemical vapor deposition (CVD) growth of single-crystal graphene on polycrystalline copper foils is a complex process affected by thermodynamics, kinetics, and growth conditions. These factors lead to the diversity of island shapes of single crystal graphene. Here, we present an experimental atomic force microscopy (AFM) study of the different shapes of single-crystal graphene grown on the inner surface of copper enclosures using the low pressure CVD technique. Most remarkably, this study indicates that graphene single crystal appears to form below the adjacent copper foil surface. This feature is revealed in cross sectional AFM scans of the height, which indicate that the graphene surface lies below the neighboring foil surface by ∼15–30 nm. Our results also show that an impurity assisted growth mechanism governs the growth of single crystal graphene via isotropic diffusion, producing two-fold, four-fold, and six-fold symmetries in the resulting flakes. In addition, single crystal graphene produced via anisotropic diffusion is also present here, but they do not exhibit signs of an impurity assisted growth mechanism. Finally, we find that strain relaxation in two-fold and four-fold symmetric graphene structures via isotropic diffusion is more complicated than the six-fold structures via isotropic diffusion, which results in multiple steps orientations in low symmetry structures.

Effect of Deposition Temperature on the Physical Performance of n-ZnO/p-Si Heterojunction

Comparative study of the physical characteristics of n-ZnO/p-Si heterojunction diode has been done as a function of deposition temperature in the range of 300-600 °C. Transparent conducting (TC) Zinc Oxide (ZnO) thin films were deposited by atmospheric pressure chemical vapor deposition (APCVD) technique on the p-Si(100) and glass substrates. Also, the influences of different deposition temperature on the morphology and optical properties of ZnO films were studied. Both the average surface roughness (from 62.8 to 18.8 nm) and the root mean square (from 78.2 to 24 nm) of ZnO films were decreased with the increase in the deposition temperature. Optical transmittance measurement results exhibited good transparency within the visible wavelength range for the films prepared at a temperature above 400 C. The current-voltage (I-V) characteristics of the heterojunction diodes exhibited rectification behavior and depend on the deposition temperature. The electrical parameters of the n-ZnO/p-Si heterojunctions were also affected by the deposition temperature. The diodes prepared at a temperature above 400 C were possessed lower reverse saturation current and high rectification ratio compared to those fabricated at a relatively lower temperature such as 300 C or 400 °C. Such low a temperature grown n-ZnO/p-Si heterojunction diodes with lower reverse saturation current could be suitable for photo-detection applications.