Deposition Of Oxide Thin Films Research Articles

Suppression of crystallization process in Atomic Layer Deposited hafnium oxide films

Research on the deposition process of atomic layer deposition (ALD) of hafnium oxide thin films is important because it enhances the performance of nonvolatile memory devices and optical coatings and contributes significantly to advancements within the semiconductor industry. In this study, the alternating deposition of tetrakis(dimethylamido) hafnium and cyclopentadienyl tris(dimethylamino) hafnium precursors was studied. Moreover, this method allows for modulation of the refractive index, surface morphology, preferred orientation and phases of the material. Theoretical calculations revealed that the two precursors selectively adsorb on different crystal planes during the ALD process, elucidating the mechanism behind their preferred orientations. This study reports a method for regulating the phase development of thin films. The crystallization of the hafnium oxide thin films was suppressed by controlling the conditions of deposition.

Exploring TMA and H2O Flow Rate Effects on Al2O3 Thin Film Deposition by Thermal ALD: Insights from Zero-Dimensional Modeling

This study investigates the impact of vapour-phase precursor flow rates—specifically those of trimethylaluminum (TMA) and deionized water (H2O)—on the deposition of aluminum oxide (Al2O3) thin films through atomic layer deposition (ALD). It explores how these flow rates influence film growth kinetics and surface reactions, which are critical components of the ALD process. The research combines experimental techniques with a zero-dimensional theoretical model, designed specifically to simulate the deposition dynamics. This model integrates factors such as surface reactions and gas partial pressures within the ALD chamber. Experimentally, Al2O3 films were deposited at varied TMA and H2O flow rates, with system conductance guiding these rates across different temperature settings. Film properties were rigorously assessed using optical reflectance methods and attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy. The experimental findings revealed a pronounced correlation between precursor flow rates and film growth. Specifically, at 150 °C, film thickness reached saturation at a TMA flow rate of 60 sccm, while at 200 °C, thickness peaked and then declined with increasing TMA flow above this rate. Notably, higher temperatures generally resulted in thinner films due to increased desorption rates, whereas higher water flow rates consistently produced thicker films, emphasizing the critical role of water vapour in facilitating surface reactions. This integrative approach not only deepens the understanding of deposition mechanics, particularly highlighting how variations in precursor flow rates distinctly affect the process, but also significantly advances operational parameters for ALD. These insights are invaluable for enhancing the application of ALD technologies across diverse sectors, including microelectronics, photovoltaics, and biomedical coatings, effectively bridging the gap between theoretical predictions and empirical results.

Enhancing perovskite solar cell performance: Investigating the impact of post-annealing on the optoelectrical and structural properties of RF-sputtered NiO films via SCAPS-1D device modeling

In recent years, perovskite solar cells have garnered significant interest in the field of solar cell research and development, primarily due to their notable efficiency. However, their limited lifespan and material defects, particularly in the interface layer and during deposition or fabrication processes, pose challenges to their widespread adoption. Innovative approaches to material processing and design are essential to addressing these issues. This paper introduces a novel method for the deposition of nickel oxide (NiO) thin films aimed at enhancing the performance of perovskite solar cells. Our study involved depositing NiO films on glass substrates using an optimised RF magnetron sputtering process at room temperature. These films were then annealed at temperatures ranging from 100 to 400 °C in an open-air setting. X-ray diffraction analysis showed that pure NiO thin films were formed. These films had a cubic crystalline structure and were mostly oriented along the (200) plane. Crucially, annealing at 100 °C significantly improved the crystallinity of the NiO films, reducing the average crystallite size from 21.05 to 6.10 nm, as evidenced by field emission scanning electron microscopy. For solar cells, this kind of microstructural refinement is very important because it changes the optical band gap, which ranged from 3.81 to 3.86 eV depending on the annealing temperature, and it also has a big effect on the films' electrical properties. The outstanding electrical characteristics of the NiO film annealed at 100 °C are particularly remarkable. We used these improved NiO films in perovskite solar cells that had a structure of FTO/NiO/MAPbI3/PCBM/Ag and ran SCAPS-1D simulations to see how well they worked. The simulation results are promising, indicating an enhancement in cell efficiency with the potential to surpass 22 %. This advancement highlights the critical role of advanced thin film deposition techniques in advancing photovoltaic technology and marks a substantial step towards unlocking the full potential of perovskite solar cells.

Effect of Time and Voltage on the Electrophoresis Deposition of Zinc Oxide Thin Films for Photovoltaic Applications

Electrophoretic deposition is a straightforward, environmentally friendly, and cost-effective technique for depositing and synthesizing nanomaterials, particularly nanofilms of semiconductors. Key parameters in electrophoresis include deposition time and voltage. Zinc oxide, a semiconductor of significant interest in solar energy research, possesses favorable characteristics, notably, a band gap value of approximately 3.33 eV. In the realm of dye-sensitized solar cells, which represent the third generation of solar cells, zinc oxide has emerged as a compelling choice for a photoanode. This study focused on depositing thin films of zinc oxide through electrophoresis and applying them as photoanodes in dye solar cells. The results demonstrated that the electrodeposited films exhibited good reflectance in the visible spectrum (~60–90%), a band gap energy of 3.28 eV, and an incident photon conversion efficiency of approximately 4.48% for the electrodeposited film at 80 V for 5 min.

Improved optoelectrical performance of nanostructured ZnO/porous silicon photovoltaic devices

This report introduced a novel technique for epitaxial bottom-up deposition of macroporous zinc oxide thin films on porous silicon (PSi) substrates. For achieving a higher surface-to-volume ratio and improving the photon trapping ability of the ZnO top layer, an optimized high-porosity PSi substrate was chosen as the template. Then, ZnO thin film was grown on the PSi substrate using the radio-frequency sputter-deposition method. The morphology of samples showed that the epitaxial layer followed the porous nature of the PSi substrate and generated a macroporous ZnO structure. The influence of post-sputtering thermal treatment at different temperatures on the structural and optical characteristics of synthesized macroporous ZnO nanostructures was studied. According to the planar surface morphologies, the average grain size of the sputtered ZnO layers heated at 300, 400, and 500 °C were 826, 1027, and 1195 nm, respectively. These results conform with the increased average crystallite size of ZnO nanostructures with higher annealing temperatures. The calculated crystallite size values were 4.14, 7.76, and 8.84 nm for the annealing temperatures of 300, 400, and 500 °C, respectively. The optical properties of the deposited thin film were improved due to the annealing process at higher temperatures. The highest light absorption coefficient was reported for the thin film annealed at 500 °C. Next, prepared macroporous n-ZnO/p-PSi samples were used to fabricate heterojunction solar cells, and their electrical properties were studied at room temperature. The optoelectrical results showed improved performance of the fabricated devices with higher annealing temperatures. The results showed an enhanced efficiency of 15.08 % for the optimized device with an annealing temperature of 500 °C, which is assigned to its increased surface and enhanced exciton generation. Moreover, this device showed lower series resistance of 4.74 Ω and higher shunt resistance of 2.98 KΩ compared to other devices with lower annealing temperatures.

Deposition and photoluminescence of zinc gallium oxide thin films with varied stoichiometry made by reactive magnetron co-sputtering

This paper reports on the deposition and photoluminescence of amorphous and crystalline thin films of zinc gallium oxide with Ga:Zn atomic ratio varied between 0.3 and 5.7. The films are prepared by reactive direct current magnetron co-sputtering from liquid/solid gallium/zinc targets onto fused quartz substrates; the temperature of the substrate is varied from room temperature (RT) to 800 °C. The sputtering process is effectively controlled by fixing the sputtering power of one of the targets and controlling the power of the other target by plasma optical emission spectroscopy. The method, in conjunction with oxygen flow adjustment, enables the production of near-stoichiometric films at any temperature used. The composition analysis suggests a few at% oxygen deficiency in the films. The resulting deposition rate is at least an order of magnitude higher compared to the commonly used radio-frequency sputtering from a ceramic ZnO:Ga2O3 target. Deposited onto unheated substrates, the films with Ga:Zn ≈ 2 are X-ray amorphous. Well-defined X-ray diffraction peaks of spinel ZnGa2O4 start to appear at a substrate temperature of 300 °C. The surface of the as-deposited films is dense and exhibits a fine-featured structure observed in electron microscopy images. Increasing the deposition temperature from RT to 800 °C eliminates defects and improves crystallinity, which for the films with Ga:Zn ratio close to 2 results in an increase in the optical band gap from 4.6 eV to 5.1 eV. Room temperature photoluminescence established the main peak at 3.1 eV (400 nm); a similar peak in Ga2O3 is ascribed to oxygen-vacancy related transitions. A prominent feature around 2.9 eV (428 nm) is attributed to self-activation center of the octahedral Ga-O groups in the spinel lattice of ZnGa2O4. It was found that photoluminescence from ZnGa2O4 depends significantly on the stoichiometric ratio between Ga and Zn and the deposition/annealing temperature.

The effect of Ar:O2 gas ratios on the structural and optical properties of RF sputter-deposited La2O3-doped ZnO thin films

Due to their unique scintillation, phosphorescence, magnetic, and catalytic properties, rare earth oxide compounds have recently become one of the most in-demand materials used in different ways. The current study investigated the impact of Ar:O2 gas flow variation on the deposition of La2O3-doped zinc oxide thin films (TFs) on silicon dioxide (SiO2) substrates using the radio frequency sputtering technique. FE-SEM analysis has shown a smooth surface topology and purity of La2O3-doped ZnO TFs. X-ray diffraction analysis exhibited a single-phase hexagonal wurtzite-type structure in TFs. A UV–Vis–IR spectrophotometer examined the optical characteristics of ZnO and La2O3-doped ZnO TFs in 300–800 nm wavelength range. The bandgap of La2O3 doped ZnO TFs changed from 2.9 to 3.1 eV as argon and oxygen concentrations in (Ar:O2) gas flow changed. A variation in optical constants such as dielectric constants, refractive index, and extinction coefficient was observed when ZnO and La2O3-doped ZnO TFs were exposed to variable (Ar:O2) gas flow ratios. The photoluminescence analysis of ZnO and La2O3-doped ZnO TFs was performed at an excitation wavelength of 330 nm. Atomic force microscopy further revealed that La2O3 doping resulted in smoother surfaces and smaller grain sizes. This comprehensive study provides valuable insights into the relationship between doping, gas composition, and the optical and structural properties of ZnO TFs. The obtained results on the optimal flow rate of argon gas provide valuable insights for determining the appropriate deposition conditions of La2O3-doped ZnO TFs, specifically for their application in solar thermal systems.

Electromechanical Control of Metal Oxide Thin Films deposition in Successive Ionic Layer Adsorption and Reaction for gas sensors devlopement

Electromechanical Control of Metal Oxide Thin Films deposition in Successive Ionic Layer Adsorption and Reaction for gas sensors devlopement

Diagnosing Time-Varying Harmonics in Low-k Oxide Thin Film (SiOF) Deposition by Using HDP CVD.

This study identified time-varying harmonic characteristics in a high-density plasma (HDP) chemical vapor deposition (CVD) chamber by depositing low-k oxide (SiOF). The characteristics of harmonics are caused by the nonlinear Lorentz force and the nonlinear nature of the sheath. In this study, a noninvasive directional coupler was used to collect harmonic power in the forward and reverse directions, which were low frequency (LF) and high bias radio frequency (RF). The intensity of the 2nd and 3rd harmonics responded to the LF power, pressure, and gas flow rate introduced for plasma generation. Meanwhile, the intensity of the 6th harmonic responded to the oxygen fraction in the transition step. The intensity of the 7th (forward) and 10th (in reverse) harmonic of the bias RF power depended on the underlying layers (silicon rich oxide (SRO) and undoped silicate glass (USG)) and the deposition of the SiOF layer. In particular, the 10th (reverse) harmonic of the bias RF power was identified using electrodynamics in a double capacitor model of the plasma sheath and the deposited dielectric material. The plasma-induced electronic charging effect on the deposited film resulted in the time-varying characteristic of the 10th harmonic (in reverse) of the bias RF power. The wafer-to-wafer consistency and stability of the time-varying characteristic were investigated. The findings of this study can be applied to in situ diagnosis of SiOF thin film deposition and optimization of the deposition process.

Characteristics of a pulsed hollow cathode discharge operated in an Ar+O[formula omitted] gas mixture and deposition of copper nickel oxide thin films

A hollow cathode discharge with a CuNi (Cu50Ni50) cathode is operated inside a vacuum chamber with Ar gas flowing through its nozzle. O2 gas is admitted to the vaccum chamber. Typical Ar+O2 gas pressures are in the range of 2–50 Pa. The energy distribution of plasma ions is investigated with the help of energy-resolved mass spectrometry. Singly charged Ar+ and molecular O2+ ions are the most abundant ionic species. Deposition rate and heat flux to a substrate increase as function of discharge current. At high pressures, the deposition rate is further increased by the directional gas flow, which becomes more focused onto the substrate. Deposited and annealed thin films are analysed by X-ray diffraction and Raman spectroscopy. As-deposited films are composed of a mixed CuxNi1−xO cubic phase with a preferred (111) orientation. Upon annealing at 600 oC, the mixed CuxNi1−xO phase separates into two sub-phases composed of NiO and CuO. Annealed films display a photoelectrochemical (PEC) activity as a photocathode. The PEC activity deteriorates with time, however. This behaviour is related to the reduction of CuO to Cu2O.

Ion expansion dynamics of laser induced multi-elemental plasmas

Ablation of multi-elemental materials by nanosecond lasers is often used to deposit oxide thin films. Understanding the ablation plume dynamics is of utmost importance to gain a detailed insight into thin film growth of materials with a complex composition. In this study, the plume expansion dynamics of several compound materials (AuCu, La0.33Ca0.67MnO3, and LiMn2O4) were characterized by measuring the angular-dependent kinetic energy (KE) distributions of ionic plasma species produced by KrF- and XeCl-excimer laser ablation in vacuum. The distributions of the lightest plume ions were found to differ fundamentally from those of other ions. The latter are similar to the energy distributions observed in single-component plumes and represent a low-energy peak and high-energy tail, while those for the lightest ions consist of at least two distinct peaks. These observations can be explained by assuming the formation of a dynamic double layer (DL) at the front of the plasma giving rise to different acceleration rates for light and heavier ions. As a consequence, heavier elements stay longer within the dynamic DL and gain larger KEs that leads to the observed ion separation. Extending these considerations into three dimensions yields an anisotropic acceleration concept for the plasma ions with high acceleration rates and longer presence within the DL normal to the target surface and lower acceleration rates and shorter time in the parallel direction.

Pseudocapacitive performance of amorphous ruthenium oxide deposited by successive ionic layer adsorption and reaction (SILAR): Effect of thickness

Developing and fabricating effective, affordable electrode materials for supercapacitors is still a challenge. Electrical conductivity, a large surface area, dynamic faster electron transport, and other customizable qualities are present in metal oxide materials while being inexpensive to manufacture. In this work, successive ionic layer adsorption and reaction (SILAR) method was employed for deposition of amorphous ruthenium oxide (RuO2) thin films of different thicknesses on a stainless steel substrate. At 1.56 mg cm−2 thickness amorphous RuO2 achieved a maximum specific capacitance (Cs) of 1146 F g−1 at a scan rate of 5 mV s−1 with 87% capacitance retention up to 5000 cycles. These findings bolster the idea of cost effective deposition of amorphous RuO2 material for supercapacitor applications.

Low-temperature synthesis of crystalline vanadium oxide films using oxygen plasmas

Vanadium oxide (VOx) compounds feature various polymorphs, including V2O5 and VO2, with attractive temperature-tunable optical and electrical properties. However, to achieve the desired material property, high-temperature post-deposition annealing of as-grown VOx films is mostly needed, limiting its use for low-temperature compatible substrates and processes. Herein, we report on the low-temperature hollow-cathode plasma-enhanced atomic layer deposition (ALD) of crystalline vanadium oxide thin films using tetrakis(ethylmethylamido)vanadium and oxygen plasma as a precursor and coreactant, respectively. To extract the impact of the type of plasma source, VOx samples were also synthesized in an inductively coupled plasma-enhanced ALD reactor. Moreover, we have incorporated in situ Ar-plasma and ex situ thermal annealing to investigate the tunability of VOx structural properties. Our findings confirm that both plasma-ALD techniques were able to synthesize as-grown polycrystalline V2O5 films at 150 °C. Postdeposition thermal annealing converted the as-grown V2O5 films into different crystalline VOx states: V2O3, V4O9, and VO2. The last one, VO2 is particularly interesting as a phase-change material, and the metal-insulator transition around 70 °C has been confirmed using temperature-dependent x-ray diffraction and resistivity measurements.

Combinative solution processing and Li doping approach to develop p-type NiO thin films with enchanced electrical properties

The deposition of nickel oxide (NiOx) thin film from an acetylacetonate source using many solution-based techniques has been avoided owing to its poor solubility in alcohol solvents. From this perspective, this work provides a systematic investigation of the development of NiOx thin film, using a combinative approach of ultrasonic spray pyrolysis (USP) and Li dopant for the synthesis and optimization of structural and optoelectronic properties of the films. An in-depth comparative analysis of nickel acetylacetonate-based precursor, employing acetonitrile and methanol as solvents, is provided. It is demonstrated that USP from acetylacetonate precursor yielded uniform, well-compact, and transparent films, with polycrystalline cubic NiOx crystal structures. By screening the deposition temperature in the range of 300–450°C, a temperature of 400°C was identified as an optimal processing temperature leading to uniform, compact, highly transparent, and p-type conductive films. At optimized deposition conditions (400°C), lithium-doped NiOx (Li:NiOx) thin film was deposited. The shift of the main (200) XRD peak position from 43.48° (0-Li:NiOx) to 43.56° (60-Li:NiOx) indicated Li incorporation into the NiOx lattice. An X-ray photoelectron spectroscopy (XPS) study was employed to unravel the incorporation of Li into the deposited Li:NiOx thin films. With the deconvolution of the Ni 2p core level for the as-deposited (0, 60)-Li:NiOx films, the intensity of Ni3+ related peak was found to increase slightly with Li doping. Furthermore, all the deposited Li:NiOx thin films showed p-type conductivity behavior, and the resistivity was reduced from 104 Ωcm (0-Li:NiOx) to 102 Ωcm (60-Li:NiOx). Based on these results, the deposited NiOx and Li:NiOx thin films suggested that USP-deposited Li:NiOx is highly suitable for application in inverted structure solar cells as the hole transport layer.

Plasma assisted atomic layer deposition NiO nanofilms for improved hybrid solid state electrochromic device

Alternate methods for deposition of electrochromic metal oxide thin films need to be explored to obtain an optimized one while designing solid state hybrid or all-inorganic electrochromic device. To continue this quest, electrochromic performance from a hybrid electrochromic device obtaining using plasma assisted atomic layer deposition (ALD) grown nickel oxide (NiO) thin film and viologen has been studied. A few tens of nanometers thick films of NiO were deposited first on silicon to optimize the deposition parameters prior to depositing on Fluorine-doped Tin Oxide (FTO)/glass substrates for fabricating the device. The structural and morphological properties of as-prepared films were analyzed by scanning electron spectroscopy (SEM), x-ray diffraction (XRD), Raman spectroscopy and x-ray photo electron spectroscopy (XPS) techniques. Thereafter, a solid state organic-inorganic hybrid electrochromic device was fabricated using Nickel oxide (NiO) and ethyl viologen (EV). The device changes its color between transparent and blue states under the potential window of ±1.7 V while taking less than 2s for toggling between the two-colored states. The device also exhibits an impressive electrochromic behavior with coloration efficiency of 118cm2/C, contrast ratio of 21% and a good cycle life/stability. The ALD grown films appeared to have advantage over other methods as it yields an atomically smooth and crack-less nano film so that proper power utilization take place for color switching. All these results open a new way to the fabrication of inorganic component to fabricate high-performance hybrid solid state electrochromic devices.

Thin Films Fabricated by Pulsed Laser Deposition for Electrocatalysis

Thin Films Fabricated by Pulsed Laser Deposition for Electrocatalysis

A theoretical study of the atomic layer deposition of HfO2 on Si(1 0 0) surfaces using tetrakis(ethylmethylamino) hafnium and water

The atomic layer deposition (ALD) of hafnium oxide (HfO2) thin film has attracted considerable attention owing to its crucial role in downscaling semiconductor devices. Herein, we theoretically investigated the reaction mechanisms during the ALD of HfO2 thin film (HfO2–ALD) on silicon (Si) surface using tetrakis(ethylmethylamino) hafnium (TEMAH) and water. By using two surface models, fully and partially hydroxylated Si(100) surfaces, we demonstrated that controlling the concentration of hydroxyl groups on the surface is important to enhance the activity for ligand-exchange reactions (LERs) of TEMAH and thereby effectively promote HfO2–ALD. During the precursor pulse, LERs on the fully hydroxylated Si(100) surface easily convert TEMAH into an unsaturated Hf atom with a low energy barrier of 25.8 kJ/mol, while mono(ethylmethylamino) hafnium (MEMAH) is obtained as the final product on the partially hydroxylated Si(100) surface with an energy barrier of 61.3 kJ/mol. The remaining ligand of the adsorbed MEMAH can be removed via LER with water during the water pulse. This work not only provides a better understanding of the conversion of TEMAH into a Hf atom on the hydroxylated Si(100) surface but also offers us more insights into the role of surface hydroxyls in the formation of HfO2 thin films.

Specific method of deposition of aluminium-doped zinc oxide thin films on flexible glass substrates

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DC Sputtering Deposition of Copper Oxide Thin Films Doped with Carbon for Efficient Solar Selective Absorbers

In this work, carbon-doped copper oxide thin films were deposited by the reactive DC sputtering method for use as selective absorbents. The properties of the DC discharge plasma were studied, using the emission spectrum, in the presence of pure argon and by mixing it with oxygen once and carbon dioxide again to know the effect of adding these gases on the properties of the resulting plasma used in the deposition of films. The structural properties of the deposited thin films prepared with different flow ratio of carbon dioxide gas were studied using x-ray diffraction. To examine the selective absorber coatings, the reflectance within the UV-Vis spectrum was measured to calculate the percentage of energy absorbed by solar radiation using numerical integration. The reflectance was also measured in the range from 2.5 to 25 μm to calculate the thermal emission of the solar heater within a temperature of 373 K. Measurements showed good efficiency as a selective absorption layer. The best absorptance of the solar spectrum (α) was 0.8750, and the lowest emittance (ε) in the infrared region was 0.254 at 25% percentage of carbon dioxide in the reactive gas of the sputtering system. So, this ratio has the highest efficiency as a selective absorber.

Stoichiometry and Morphology Analysis of Thermally Deposited V2O5-x Thin Films for Si/V2O5-x Heterojunction Solar Cell Applications.

In recent decades, dopant-free Si-based solar cells with a transition metal oxide layer have gained noticeable research interest as promising candidates for next-generation solar cells with both low manufacturing cost and high power conversion efficiency. Here, we report the effect of the substrate temperature for the deposition of vanadium oxide (V2O5−x, 0 ≤ X ≤ 5) thin films (TFs) for enhanced Si surface passivation. The effectiveness of SiOx formation at the Si/V2O5−x interface for Si surface passivation was investigated by comparing the results of minority carrier lifetime measurements, X-ray photoelectron spectroscopy, and atomic force microscopy. We successfully demonstrated that the deposition temperature of V2O5−x has a decisive effect on the surface passivation performance. The results confirmed that the aspect ratio of the V2O5−x islands that are initially deposited is a crucial factor to facilitate the transport of oxygen atoms originating from the V2O5−x being deposited to the Si surface. In addition, the stoichiometry of V2O5−x TFs can be notably altered by substrate temperature during deposition. As a result, experimentation with the fabricated Si/V2O5−x heterojunction solar cells confirmed that the power conversion efficiency is the highest at a V2O5−x deposition temperature of 75 °C.