Laser-assisted Chemical Vapor Deposition Research Articles

Diamond coatings on femtosecond-laser-textured stainless steel 316 surfaces for enhanced adherence

A challenge for directly coating diamond on metallic substrates is the large residual stress near their interfaces due to the large mismatch in the coefficients of thermal expansion (CTEs) that leads to cracking or delamination of the diamond coatings from the substrates. In this work, femtosecond (fs)-laser texturing was applied to fabricate various periodic microgrids on stainless steel (SS) 316 substrates for enhancing the adherence between the SS 316 substrates and the diamond coatings grown using the laser-assisted combustion flame chemical vapor deposition (CVD). Through adjusting the dimensions of the microgrids with different fs scanning parameters, the diamond coatings with a maximum thickness of 19 μm can be grown with quality factors up to 96 % as analyzed by Raman spectroscopy. The corresponding large diamond crystals with an average grain size of 9 μm can be obtained on SS316 substrates by optimizing the fs-laser texturing process. The enhanced adherence between the SS 316 substrates and diamond coatings can be attributed to the stress relief and the improved mechanical bonding. The growth kinetics of the diamond coatings on fs-laser-textured SS 316 substrates were also revealed through the phase constitutions and morphology characteristics. This work is anticipated to provide a new strategy and guidance for the growth of diamond coatings on metallic materials with strong adherence at the interfaces.

Preparation of silicon carbide and tantalum carbonitride composite with high hardness and moderate elastic modulus by laser chemical vapor deposition for anti-erosion protective coatings

Maintaining the harness of silicon carbide (SiC), while reducing Young's modulus of ceramic coatings is crucial for developing highly durable coating systems. This study demonstrated the growth of SiC and tantalum carbonitride (TaCN) composite films with high hardness and low modulus using laser-assisted chemical vapor deposition (CVD) with metal-organic precursors. The effects of deposition temperature on phases, chemical compositions, binding states, microstructures and mechanical properties were investigated. The film prepared at a deposition temperature of 1100 °C were grown at a deposition rate of 81.8 μm h−1, which comprised low-crystallinity SiC and TaCN grains smaller than 10 nm finely mixed and dispersed each other, forming a nanometric mosaic structure. The cross-sectional nanoindentation tests revealed a reduced Young's modulus (E*) of 238.2 GPa and a hardness (H) of 30.4 GPa, corresponding to H/E* and H3/E*2 values of 0.127 and 0.493 GPa, respectively. The SiC–TaCN nanocomposite film exhibited superior durability in erosion tests using a zirconia slurry at 20 kPa, compared with a monolithic SiC film and a silicon nitride substrate.

Trap characterization of high-growth-rate laser-assisted MOCVD GaN

A detailed study comparing defect incorporation between laser-assisted metal-organic chemical vapor deposition (MOCVD)-grown GaN and conventional low- and high-growth-rate MOCVD GaN was conducted. Using deep-level transient and optical spectroscopy, traps throughout the bandgap were characterized where traps were found at EC-0.25 eV, EC-0.57 eV, EC-0.72 eV, EC-0.9 eV, EC-1.35 eV, EC-2.6 eV, and EC-3.28 eV in all three samples. This indicates no new traps were observed in the laser-assisted MOCVD GaN sample. Overall, the trap concentrations in the laser-assisted MOCVD sample were ∼2× higher than the optimal low-growth-rate sample, but this is primarily due to the increase in gallium vacancy EC-2.6 eV and carbon-related EC-3.28 eV trap concentrations. The EC-0.9 eV trap concentration was ∼2× higher in the laser-assisted sample, so proton irradiation experiments were conducted to identify the physical source of this level. The results indicated this was a native point defect likely related to gallium interstitials. Overall, this study shows that the laser-assisted MOCVD growth method is promising for future thick, high-quality GaN epilayers after further growth optimizations.

Growth and scintillation properties of Ce 3+:LuAG–Al2O3 chemically deposited eutectics

Directionally solidified eutectics (DSEs) in Al2O3-based systems have been studied as high-temperature structural ceramics, also recently attracting attention as a phosphor screen for high-resolution radiation imaging. However, it is difficult to obtain uniform and thinly processed DSE in large areas. Here, we report a chemically deposited eutectic (CDE) of Lu3Al5O12 (LuAG)–Al2O3 using a laser-assisted chemical vapor deposition method. The Ce3+-doped LuAG lamella were epitaxially grew with an α-Al2O3 matrix on an r-cut sapphire substrate. The Ce3+:LuAG–α-Al2O3 CDE film exhibited green emissions due to the 5d–4f transitions of the Ce3+ center under UV light and α-/X-ray irradiations. The α-ray dose in the Ce3+:LuAG phase was estimated with Monte Carlo simulations to study a scintillation light yield of the CDE film. The X-ray radiograph of the semiconductor storage device was successfully obtained using a 15-μm-thick Ce3+:LuAG–α-Al2O3 CDE film as an X-ray phosphor screen.

Laser-Assisted Growth of Carbon-Based Materials by Chemical Vapor Deposition

Carbon-based materials (CBMs) such as graphene, carbon nanotubes (CNT), highly ordered pyrolytic graphite (HOPG), and pyrolytic carbon (PyC) have received a great deal of attention in recent years due to their unique electronic, optical, thermal, and mechanical properties. CBMs have been grown using a variety of processes, including mechanical exfoliation, pulsed laser deposition (PLD), and chemical vapor deposition (CVD). Mechanical exfoliation creates materials that are irregularly formed and tiny in size. On the other hand, the practicality of the PLD approach for large-area high-quality CMB deposition is quite difficult. Thus, CVD is considered as the most effective method for growing CBMs. In this paper, a novel pulsed laser-assisted chemical vapor deposition (LCVD) technique was explored to determine ways to reduce the energy requirements to produce high quality CBMs. Different growth parameters, such as gas flow rate, temperature, laser energy, and deposition time were considered and studied thoroughly to analyze the growth pattern. CBMs are grown on Si and Cu substrates, where we find better quality CBM films on Cu as it aids the surface solubility of carbon. Raman spectroscopy confirms the presence of high-quality PyC which is grown at a temperature of 750 °C, CH4 gas flow rate of 20 sccm, a laser frequency of 10 Hz, and an energy density of 0.116 J/cm2 per pulse. It is found that the local pulsed-laser bombardment helps in breaking the carbon-hydrogen bonds of CH4 at a much lower substrate temperature than its thermal decomposition temperature. There is no significant change in the 2D peak intensity in the Raman spectrum with the further increase in temperature which is the indicator of the number of the graphene layer. The intertwined graphene flakes of the PyC are observed due to the surface roughness, which is responsible for the quenching in the Raman 2D signal. These results will provide the platform to fabricate a large area single layer of graphene, including the other 2D materials, on different substrates using the LCVD technique.

Enhanced surface dynamics and magnetic switching of α-Fe2O3 films prepared by laser assisted chemical vapor deposition

In this work, thin hematite films (α-Fe2O3) were fabricated by laser-assisted chemical vapor deposition (LCVD) method using Ar+ laser source. The deposited α-Fe2O3 films were subjected to annealing treatment in O2 and N2 atmosphere at 350 and 400 °C, respectively. The obtained haematite films were doped by bombarding N-ions (3.63 × 1015–6.63 × 1015 ions/cm2) at 350 °C in a furnace at 350 °C. The structure, optical, and magnetic properties were evaluated and compared by X-ray diffraction (XRD), Raman spectroscopy, ultraviolet–visible spectroscopy (UV Vis), and superconducting quantum interference device (SQUID) with vibration sample magnetometer (VSM). The surface topography and ripple formation on N-doped α-Fe2O3 films before and after N-ion at different fluences (0.63 × 1015–6.63 × 1015 ions/cm2) were studied by Rutherford backscattering (RBS) and atomic force microscopy (AFM). Hematite thin films had a rhombohedral structure and annealing of hematite films in N2 atmosphere at 350 °C, caused the formation of uniform surface topography with a lower surface roughness as compared to those annealed in O2 atmosphere. Besides, the hematite films doped with N2 had finer ripples across the surface which increased with higher nitrogen fluence. The photoconductivity mechanism of these films in various UV, Indigo, Green, and dark region is also reported here which can serve as a blueprint for material design in various photochemical, catalytic, and magnetic storage applications.

Luminescent MoS2 Quantum Dots with Tunable Operating Potential for Energy-Enhanced Aqueous Supercapacitors.

Wide band gap luminescent MoS2 quantum dots (QDs) and MoS2 nanocrystals (NCs) have been synthesized by using laser-assisted chemical vapour deposition and used as an electrode material in supercapacitors. Size-dependent properties of the MoS2 QDs and NCs were examined by UV–vis absorption, photoluminescence, and Raman spectroscopy. The morphological evolution of the NCs and QDs were characterized by using field emission scanning electron microscopy, high-resolution transmission electron microscopy, and atomic force microscopy. The as-synthesized uniform QDs with a size of ∼2 nm exhibited an extended electrochemical potential window of 0.9 V with a specific capacitance value of 255 F/g, while the NCs values were 205 F/g and 0.8 V and the pristine MoS2 with values of 105 F/g and 0.6 V at a scan rate of 1 mV s–1. A shorter conductive pathway and 3D quantum confinement of MoS2 QDs that exhibited a higher number of active sites ensure that the efficient charge storage kinetics along with the intercalation processes at the available edge sites enable significant widening of operating potential window and enhance the capacitance. The symmetric device constructed with the QDs showed a remarkable device capacitance of 50 F/g at a scan rate of 1 mV s–1 with an energy density of ∼5.7 W h kg–1 and achieved an excellent cycle stability of 10,000 consecutive cycles with ∼95% capacitance retention.

Two-step fabrication of thin film encapsulation using laser assisted chemical vapor deposition and laser assisted plasma enhanced chemical vapor deposition for long-lifetime organic light emitting diodes

A thin film encapsulation layer was fabricated through two-sequential chemical vapor deposition processes for organic light emitting diodes (OLEDs). The fabrication process consists of laser assisted chemical vapor deposition (LACVD) for the first silicon nitride layer and laser assisted plasma enhanced chemical vapor deposition (LAPECVD) for the second silicon nitride layer. While SiN x thin films fabricated by LAPECVD exhibits remarkable encapsulation characteristics, OLEDs underneath the encapsulation layer risk being damaged during the plasma generation process. In order to prevent damage from the plasma, LACVD was completed prior to the LAPECVD as a buffer layer so that the laser during LACVD did not damage the devices because there was no direct irradiation to the surface. This two-step thin film encapsulation was performed sequentially in one chamber, which reduced the process steps and increased fabrication time. The encapsulation was demonstrated on green phosphorescent OLEDs with I–V-L measurements and a lifetime test. The two-step encapsulation process alleviated the damage on the devices by 19.5% in external quantum efficiency compared to the single layer fabricated by plasma enhanced chemical vapor deposition. The lifetime was increased 3.59 times compared to the device without encapsulation. The composition of the SiNx thin films was analyzed through Fourier-transform infrared spectroscopy (FTIR). While the atomic bond in the layer fabricated by LACVD was too weak to be used in encapsulation, the layer fabricated by the two-step encapsulation did not reveal a Si–O bonding peak but did show a Si–N peak with strong atomic bonding. • Thin film encapsulation by laser assisted plasma enhanced chemical vapor deposition. • Buffer layer by laser assisted chemical vapor deposition prior to encapsulation. • Increase of stability and protection of plasma damage through in-line pre-deposition. • 3.59 times increased LT80 in green phosphorescent organic light emitting diodes.

A reactive molecular dynamics study on the mechanical properties of a recently synthesized amorphous carbon monolayer converted into a nanotube/nanoscroll.

Recently, laser-assisted chemical vapor deposition has been used to synthesize a free-standing, continuous, and stable monolayer amorphous carbon (MAC). MAC is a pure carbon structure composed of randomly distributed five, six, seven, and eight atom rings, which is different from that of disordered graphene. More recently, amorphous MAC-based nanotubes (a-CNT) and nanoscrolls (a-CNS) were proposed. In this work, we have investigated (through fully atomistic reactive molecular dynamics simulations) the mechanical properties and sublimation points of pristine and a-CNT and a-CNS. The results showed that a-CNT and a-CNS have distinct elastic properties and fracture patterns compared to those of their pristine analogs. Both a-CNT and a-CNS presented a non-elastic regime before their total rupture, whereas the CNT and CNS underwent a direct conversion to fractured forms after a critical strain threshold. The critical strain values for the fracture of the a-CNT and a-CNS are about 30% and 25%, respectively, and they are lower than those of the corresponding CNT and CNS cases. Although less resilient to tension, the amorphous tubular structures have similar thermal stability in relation to the pristine cases with sublimation points of 5500 K, 6300 K, 5100 K, and 5900 K for a-CNT, CNT, a-CNS, and CNS, respectively. An interesting result is that the nanostructure behavior is substantially different depending on whether it is a nanotube or a nanoscroll, thus indicating that the topology plays an important role in defining its elastic properties.

Direct writing of graphite thin film by laser-assisted chemical vapor deposition

This study reports the direct writing of low-resistance graphite film strip of 25 μm width and ∼65 nm height on nickel substrates by laser-assisted chemical vapor deposition (LCVD). Raman spectra of the LCVD graphite showed no D-band, confirming that it had little defects. The G-band was nearly constant but the 2D-band showed variations in shape and intensity. A detailed analysis of the 2D-band revealed that the LCVD graphite is a mixture of highly ordered graphite and turbostratic graphite. An observation of the stacking feature by transmission electron microscope further confirmed that the layers close to substrate was closely packed, whereas the layer interspacing gradually increased with distance, transforming into turbostratic graphite. The resistivity of LCVD graphite estimated from the sheet resistance measured by the 4-point method was 2.45 × 10−5 Ω m.

Role of a 193 nm ArF Excimer Laser in Laser-Assisted Plasma-Enhanced Chemical Vapor Deposition of SiNx for Low Temperature Thin Film Encapsulation.

In this study, silicon nitride thin films are deposited on organic polyethylene-naphthalate (PEN) substrates by laser assisted plasma enhanced chemical vapor deposition (LAPECVD) at a low temperature (150 °C) for the purpose of evaluating the encapsulation performance. A plasma generator is placed above the sample stage as conventional plasma enhanced chemical vapor deposition (PECVD) configuration, and the excimer laser beam of 193 nm wavelength illuminated in parallel to the sample surface is coupled to the reaction zone between the sample and plasma source. Major roles of the laser illumination in LAPECVD process are to compete with or complement the plasma decomposition of reactant gases. While a laser mainly decomposes ammonia molecules in the plasma, it also contributes to the photolysis of silane in the plasma state, possibly through the resulting hydrogen radicals and the excitation of intermediate disilane products. It will also be shown that the LAPECVD with coupled laser illumination of 193 nm wavelength improves the deposition rate of silicon nitride thin film, and the encapsulation performance evaluated via the measurement of water vapor transmission rate (WVTR).

Synthesis and properties of free-standing monolayer amorphous carbon.

Bulk amorphous materials have been studied extensively and are widely used, yet their atomic arrangement remains an open issue. Although they are generally believed to be Zachariasen continuous random networks1, recent experimental evidence favours the competing crystallite model in the case of amorphous silicon2-4. In two-dimensional materials, however, the corresponding questions remain unanswered. Here we report the synthesis, by laser-assisted chemical vapour deposition5, of centimetre-scale, free-standing, continuous and stable monolayer amorphous carbon, topologically distinct from disordered graphene. Unlike in bulk materials, the structure of monolayer amorphous carbon can be determined by atomic-resolution imaging. Extensive characterization by Raman and X-ray spectroscopy and transmission electron microscopy reveals the complete absence of long-range periodicity and a threefold-coordinated structure with a wide distribution of bond lengths, bond angles, and five-, six-, seven- and eight-member rings. The ring distribution is not a Zachariasen continuous random network, but resembles the competing (nano)crystallite model6. We construct a corresponding model that enables density-functional-theory calculations of the properties of monolayer amorphous carbon, in accordance with observations. Direct measurements confirm that it is insulating, with resistivity values similar to those of boron nitride grown by chemical vapour deposition. Free-standing monolayer amorphous carbon is surprisingly stable and deforms to a high breaking strength, without crack propagation from the point of fracture. The excellent physical properties of this stable, free-standing monolayer amorphous carbon could prove useful for permeation and diffusion barriers in applications such as magnetic recording devices and flexible electronics.

Catalyst-Free Growth of MoS2 Nanorods Synthesized by Dual Pulsed Laser-Assisted Chemical Vapor Deposition and Their Structural, Optical and Electrical Properties

Molybdenum disulfide (MoS2) nanorods (NRs) were synthesized from bulk MoS2 using laser-assisted chemical vapor deposition. A q-switched Nd:YAG laser with combined beam wavelengths of 1064┬anm and 532┬anm was used to ablate a solid MoS2 target. A vaporΓCosolid process at a furnace temperature of 1000┬░C was found to support the growth of MoS2 NRs without the need for any metal catalyst. Powder x-ray diffraction analysis (PXRD), field emission scanning electron microscopy, high-resolution transmission electron microscopy, Raman spectroscopy, and ultravioletΓCovisible (UVΓCoVis) and photoluminescence (PL) spectroscopy were used to characterize the structural and optical properties of MoS2 NRs. The PXRD revealed the crystallinity and phase purity of the as-synthesized NRs, while electron microscopy showed that MoS2 NRs had lengths in the range of 0.5ΓCo1.2┬a╬╝m and widths between 40┬anm and 160┬anm. UVΓCoVis absorption spectra exhibited broad absorption, and PL measurements showed a sharp emission peak at 379┬anm. Tauc plot calculations determined that the MoS2 NRs showed a direct transition. The electrical conductivity of the NRs was found to be 317.95┬aS/cm. In comparison with the MoS2 nanoparticles, the MoS2 NRs showed higher conductivity due to the in-plane electron transport, which is higher in NRs.

Research progress on SiCN ceramic prepared at low temperature by chemical vapor deposition

Chemical vapor deposition (CVD) is a new technology for preparing inorganic materials which possess some advantages, such as lower preparation temperature, uniform and compact microstructure, and near-size molding, so it is one of the common methods to prepare functional ceramics. In the paper, several common chemical vapor deposition methods like atmospheric chemical vapor deposition, low-pressure chemical vapor deposition, plasma-enhanced chemical vapor deposition and laser-assisted chemical vapor deposition are reviewed, because the microstructure and performance of functional ceramics are greatly influenced by their fabrication methods. In addition, the deposition parameters of Si-C-N absorbing ceramics which are deposited at lower temperature by low-pressure chemical vapor deposition are optimized. It is proposed that low-pressure chemical vapor deposition is the main method for preparing the advanced EMW absorbing ceramics.

Laser assisted synthesis of inorganic fullerene like MoS2-Au nanohybrid and their cytotoxicity against human monocytic (THP-1) cells

Here in, we report the investigation of the immunotoxicity of gold nanoparticles decorated on inorganic fullerene like MoS2 nanostructure (IFMoS2- AuNPs) on the THP-1 immune cell line. The MoS2 nanoparticle with fullerene like nanostructure (IFMoS2) was synthesized by double pulsed laser-assisted chemical vapour deposition (LCVD) method from bulk MoS2 at the temperature of 700 °C. The MoS2 inorganic fullerene-like nanoparticles grown by vapour-solid process (VS). The surface of the IFMoS2 was decorated with gold nanoparticles (AuNPs) to develop the semiconductor biocompatibility interface. The IFMoS2 are typically with diameters 20–50 nm as observed from the electron microscopy analysis. The stability of IFMoS2-AuNPs were examined by dynamic light scattering (DLS) and zeta potential measurements. The decoration of AuNPs on IFMoS2 surface was analyzed by UV–Vis, FTIR, PXRD, FESEM, EDX with elemental mapping and HRTEM measurement. The in vitro cytotoxicity evaluation of the FMoS2-AuNPs was determined on acute monocytic leukemic cells (THP-1) in which cell viability, caspase activity (CASP -3&7/CASP -8/CASP -9) and cell- structural changes were assessed. From FESEM revealed that IFMoS2-AuNPs induced apoptosis in THP-1 cells. Further, THP-1 cell viability markedly decreased at higher IFMoS2-AuNPs concentrations (65–100 μg/ml), indicating its potential as a chemotherapeutic agent in the treatment of human monocytic leukemia.

Thermally Stable and Electrically Conductive, Vertically Aligned Carbon Nanotube/Silicon Infiltrated Composite Structures for High-Temperature Electrodes.

Traditional ceramic-based, high-temperature electrode materials (e.g., lanthanum chromate) are severely limited due to their conditional electrical conductivity and poor stability under harsh circumstances. Advanced composite structures based on vertically aligned carbon nanotubes (VACNTs) and high-temperature ceramics are expected to address this grand challenge, in which ceramic serves as a shielding layer protecting the VACNTs from the oxidation and erosive environment, while the VACNTs work as a conductor. However, it is still a great challenge to fabricate VACNT/ceramic composite structures due to the limited diffusion of ceramics inside the VACNT arrays. In this work, we report on the controllable fabrication of infiltrated (and noninfiltrated) VACNT/silicon composite structures via thermal chemical vapor deposition (CVD) [and laser-assisted CVD]. In laser-assisted CVD, low-crystalline silicon (Si) was quickly deposited at the VACNT subsurfaces/surfaces followed by the formation of high-crystalline Si layers, thus resulting in noninfiltrated composite structures. Unlike laser-assisted CVD, thermal CVD activated the precursors inside and outside the VACNTs simultaneously, which realized uniform infiltrated VACNT/Si composite structures. The growth mechanisms for infiltrated and noninfiltrated VACNT/ceramic composites, which we attributed to the different temperature distributions and gas diffusion mechanism in VACNTs, were investigated. More importantly, the as-farbicated composite structures exhibited excellent multifunctional properties, such as excellent antioxidative ability (up to 1100 °C), high thermal stability (up to 1400 °C), good high velocity hot gas erosion resistance, and good electrical conductivity (∼8.95 Sm-1 at 823 K). The work presented here brings a simple, new approach to the fabrication of advanced composite structures for hot electrode applications.

Laser-assisted chemical vapor deposition setup for fast synthesis of graphene patterns.

An automatic setup based on the laser-assisted chemical vapor deposition method has been developed for the rapid synthesis of graphene patterns. The key components of this setup include a laser beam control and focusing unit, a laser spot monitoring unit, and a vacuum and flow control unit. A laser beam with precision control of laser power is focused on the surface of a nickel foil substrate by the laser beam control and focusing unit for localized heating. A rapid heating and cooling process at the localized region is induced by the relative movement between the focalized laser spot and the nickel foil substrate, which causes the decomposing of gaseous hydrocarbon and the out-diffusing of excess carbon atoms to form graphene patterns on the laser scanning path. All the fabrication parameters that affect the quality and number of graphene layers, such as laser power, laser spot size, laser scanning speed, pressure of vacuum chamber, and flow rates of gases, can be precisely controlled and monitored during the preparation of graphene patterns. A simulation of temperature distribution was carried out via the finite element method, providing a scientific guidance for the regulation of temperature distribution during experiments. A multi-layer graphene ribbon with few defects was synthesized to verify its performance of the rapid growth of high-quality graphene patterns. Furthermore, this setup has potential applications in other laser-based graphene synthesis and processing.

Laser assisted chemical vapor deposition of nanostructured NaTaO3 and SrTiO3 thin films for efficient photocatalytic hydrogen evolution

In this work, we report the preparation of nanostructured NaTaO3 and SrTiO3 thin films on stainless steel substrates by laser assisted chemical vapor deposition (LCVD) and their application as photocatalysts for hydrogen evolution under UV light. The effect of the deposition conditions on the compositions and microstructures of the materials is discussed, and an integral study of the influence of the structural, morphological, optical and photoelectrochemical properties of the films on their catalytic activities for hydrogen production is presented through X-ray diffraction (XRD), scanning electron microscopy (SEM), UV–vis diffuse reflectance spectroscopy (DRS), photoluminescence spectroscopy (PL) and electrochemical impedance spectroscopy (EIS) analyses. The LCVD process allows for the growth of films with attractive microstructures for photocatalytic applications, leading to a roof-like morphology in the case of orthorhombic NaTaO3 and a cauliflower-like morphology for cubic SrTiO3, which promote an enhanced charge separation and transference process and a higher photocatalytic efficiency compared to the photocatalysts prepared as powders. Orthorhombic NaTaO3 exhibits a hydrogen evolution rate of 5672μmolg−1h−1, and SrTiO3 generates only 494μmolg−1h−1, which are significantly higher than the activities of the materials prepared as powders. This improvement is attributed to the microstructure of the films prepared by LCVD and their superior optical, structural and photoelectrochemical properties. The results of the evaluation of the catalytic activity of the films prepared in this work by LCVD demonstrate the attainment of stable photocatalysts with a competitive performance compared to similar materials prepared by alternative methods.

Resonant and nonresonant vibrational excitation of ammonia molecules in the growth of gallium nitride using laser-assisted metal organic chemical vapour deposition

The influence of exciting ammonia (NH3) molecular vibration in the growth of gallium nitride (GaN) was investigated by using an infrared laser-assisted metal organic chemical vapor deposition method. A wavelength tunable CO2 laser was used to selectively excite the individual vibrational modes. Resonantly exciting the NH-wagging mode (v2) of NH3 molecules at 9.219 μm led to a GaN growth rate of 84 μm/h, which is much higher than the reported results. The difference between the resonantly excited and conventional thermally populated vibrational states was studied via resonant and nonresonant vibrational excitations of NH3 molecules. Resonant excitation of various vibrational modes was achieved at 9.219, 10.35, and 10.719 μm, respectively. Nonresonant excitation was conducted at 9.201 and 10.591 μm, similar to conventional thermal heating. Compared to nonresonant excitation, resonant excitation noticeably promotes the GaN growth rate and crystalline quality. The full width at half maximum value of the XRD rocking curves of the GaN (0002) and GaN (10–12) diffraction peaks decreased at resonant depositions and reached its minimum value of 45 and 53 arcmin, respectively, at the laser wavelength of 9.219 μm. According to the optical emission spectroscopic studies, resonantly exciting the NH3 v2 mode leads to NH3 decomposition at room temperature, reduces the formation of the TMGa:NH3 adduct, promotes the supply of active species in GaN formation, and, therefore, results in the increased GaN growth rate.

Low Temperature Deposition of Inorganic Thin Films by Ultraviolet Laser-Assisted Chemical Vapor Deposition

Low Temperature Deposition of Inorganic Thin Films by Ultraviolet Laser-Assisted Chemical Vapor Deposition