Film Growth Research Articles

Recent Applications and Future Trends of Nanostructured Thin Films-Based Gas Sensors Produced by Magnetron Sputtering

The field of gas sensors has been developing for the last year due to the necessity of characterizing compounds and, in particular, volatile organic compounds whose detection can be of special interest in a vast range of applications that extend from clinical evaluation to environmental monitoring. Among all the potential techniques to develop sensors, magnetron sputtering has emerged as one of the most suitable methodologies for the production of large-scale uniform coatings, with high packing density and strong adhesion to the substrate at relatively low substrate temperatures. Furthermore, it presents elevated deposition rates, allows the growth of thin films with high purity, permits a precise control of film thickness, enables the simple manufacturing of sensors with low power consumption and, consequently, low costs involved in the production. This work reviewed all the current applications of gas sensors developed through magnetron sputtering in the field of VOCs assessment by gathering the most relevant scientific works published. A total of 10 compounds were considered for this work. Additionally, 13 other compounds were identified as promising targets and classified as future trends in this field. Overall, this work summarizes the state-of-the-art in the field of gas sensors developed by magnetron sputtering technology, allowing the scientific community to take a step forward in this field and explore new research areas.

Epitaxial growth of HfB2 thin films on Si(111) by magnetron sputtering

Epitaxial growth of HfB2 thin films on Si(111) by magnetron sputtering

Investigation of thermally induced surface composition and morphology variation of magnetron sputtered Sb2Se3 absorber layer for thin film solar cells

One of the most promising semiconductor materials for the development of sustainable thin-film solar cell technology is antimony selenide (Sb2Se3). Its excellent optical and electrical properties have drawn attention lately for potential application in thin-film solar cells. In this study, Sb2Se3 films deposited using the direct current (DC) magnetron sputtering technique have been subjected to a post-annealing process without an extra selenium supply at temperatures between 150 and 450 °C. Without an extra selenium supply, the impact of post-annealing temperature on the surface composition as well as the physical properties of the fabricated films was investigated. The overall evaluations revealed that the post-annealing temperature is highly efficient in altering the physical properties of the Sb2Se3 absorber thin films. We further observed that the post-annealing process improved the crystallization and the heat treatment temperature quite affected preferential orientation. The surface morphology of films exhibited structural deformation at high post-annealing temperatures (> 350 °C). According to optical and electrical characterizations, respectively, the optical energy gap and the resistivity of Sb2Se3 films reduced with an increment in the post-annealing temperature. Based on the XPS result, the variation in temperature of post-annealing led to a change in the surface composition of the films. The findings on the growth of Sb2Se3 thin films indicate the existence of an intermediate growth temperature that permits the growth of Sb2Se3 films to be optimized. The study’s conclusions can serve as a guide to the growth of Sb2Se3 thin films with the desired crystallinity, surface morphology, and composition for thin film solar cell applications.

Heterogeneous Morphologies and Hardness of Co-Sputtered Thin Films of Concentrated Cu-Mo-W Alloys

Heterogeneous microstructures in Cu-Mo-W alloy thin films formed by magnetron co-sputtering immiscible elements with concentrated compositions are characterized using scanning transmission electron microscopy (STEM) and nanoindentation. In this work, we modified the phase separated structure of a Cu-Mo immiscible system by adding W, which impedes surface diffusion during film growth. The heterogeneous microstructures in the Cu-Mo-W ternary system exhibited bicontinuous matrices and agglomerates composed of Mo(W)-rich phase. This is unique, as these are the slower-diffusing species, contrasting past reports of binary Cu-Mo thin films that exhibited Cu-rich agglomerates. The bicontinuous matrices comprised of Cu-rich and Mo(W)-rich phases exhibited bilayer thicknesses of less than 5 nm. The hardness of these thin films measured using nanoindentation is reported and compared to similar multilayers and nanocomposites in binary systems.

Effect of substrate temperature on the growth mechanism of FeSe superconducting films

Abstract Among all the iron-based superconductors (IBSs), Fe-chalcogenides (Fe-Ch) possess the advan tages of simple structure, non-toxicity, low anisotropy and the potential for high-field applications.One of the most effective methods for preparing Fe-Ch films is pulsed laser deposition (PLD). However, high quality film growth is challenged by the significant volatility difference between the iron
and chalcogens (S, Se, Te), which affects stoichiometric transfer from target to substrate and subsequently impacts superconductivity. Currently, there is limited research on the correlation between the growth mechanism and preparation conditions of Fe-Ch films, particularly in explaining chalcogen volatility during deposition. Technically, PLD offers various adjustable parameters, among
which the substrate temperature (Ts) is the most critical one affecting film quality. It governs particle behavior on the substrate including adsorption, diffusion, bonding reactions, crystallization processes while also strongly affecting volatilization rates. In this study, we fabricated a series of FeSe films using PLD at different Ts ranging from 25 ℃ to 750 ℃.We reveal in detail the impact of
competitive processes between Se volatilization and reactive crystallization of Fe/Se on film quality. The optimal film was obtained at Ts=500 ℃ with a composition ratio of Fe1.01Se. We also investigate the correlations between Ts and film crystallinity, surface morphology, along with their influence on superconductivity. Additionally, the pinning mechanism in FeSe film grown at the
optimal Ts was briefly analyzed. Our results provide reliable experimental evidence regarding the growth mechanism of FeSe films while revealing comprehensive insights into how Ts affects both film quality and performance.

Low-resistivity Ohmic contacts of Ti/Al on few-layered 1T'-MoTe2/2H-MoTe2 heterojunctions grown by chemical vapor deposition.

This study explores the phase-controlled growth of few-layered 2H-MoTe2, 1T'-MoTe2, and 2H-/1T'-MoTe2 heterostructures and their impacts on metal contact properties. Cold-wall chemical vapor deposition (CW-CVD) with varying growth rates of MoOx and reaction temperatures with Te vapors enabled the growth of continuous thin films of either 1T'-MoTe2 or 2H-MoTe2 phases on two-inch sapphire substrates. This methodology facilitates the meticulous optimization of chemical vapor deposition (CVD) parameters, enabling the realization of phase-controlled growth of few-layered MoTe2 thin films and their subsequent heterostructures. The study further investigates the influence of a 1T'-MoTe2 intermediate layer on the electrical properties of metal contacts on few-layered 2H-MoTe2. Bi-layer Ti/Al contacts directly deposited on 2H-MoTe2 exhibited Schottky behavior, indicating inefficient carrier transport. However, introducing a few-layered 1T'-MoTe2 intermediate layer between the metal and 2H-MoTe2 layers improved the contact characteristics significantly. The resulting Al/Ti/1T'-MoTe2/2H-MoTe2 contact scheme demonstrates Ohmic behavior with a specific contact resistance of around 1.7 × 10-4 Ω cm2. This substantial improvement is attributed to the high carrier concentration of the 1T'-MoTe2 intermediate layer which could be attributed tentatively to the increased tunneling events across the van der Waals gap and enhancing carrier transport between the metal and 2H-MoTe2.

Properties of phosphorus-boron co-doped c-Si quantum dots/SiNx:H thin film prepared by PECVD in-situ deposition

Co-doping of phosphorus and boron elements into crystalline silicon quantum dot (c-Si QD) is an effective approach for enhancing the photoluminescence (PL) performance. In this paper, we report on the preparation of hydrogenated silicon nitride (SiNx:H) thin films embedded with phosphorus-boron co-doped c-Si QDs via plasma enhanced chemical vapor deposition route. Mixed dilution including hydrogen (H2) and argon (Ar) is applied in the in-situ deposition process for optimizing the deposition process. The P-B co-doped c-Si QD/SiNx:H thin films exhibit a wide range of PL spectra. The emission is greatly improved especially for the short-wavelength light when compared to the SiOx:H thin film containing P-B co-doped c-Si QDs. The effects of H2/Ar flow ratio on the structural and optical characteristics of thin films are systematically investigated through a series of characterizations. Experimental results show that various properties, such as crystallinity, QD size, optical band gap and doping concentrations, are effectively controlled by tuning H2/Ar flow ratio. Based on the red-shift of QCE-related PL peak, the successful P-B co-doping into Si QDs are verified. Finally, a comprehensive discussion has been made to analyze the influence of H2-Ar mixed dilution on the film growth and impurity doping in detail in this paper.

Dark current in FTO/CZTS interface: A comprehensive comparison of practical Vs theoretical approach using SCAPS 1D

Abstract This study investigates the deposition of Cu2ZnSnS4 (CZTS) thin films on fluorine-doped tin oxide (FTO) and soda-lime glass (SLG) substrates using radio frequency (RF) sputtering at varying temperatures. A comprehensive characterization employing multiple analytical techniques was conducted. X-ray diffraction (XRD) analyses confirmed the amorphous nature of CZTS films deposited up to 200°C, while higher temperatures promoted increased crystallinity, with the presence of (112) and (220) planes observed at 300°C and 400°C. Rietveld refinement using Profex software revealed an increase in crystallite size with deposition temperature for films grown at 300°C and 400°C. Optical characterization through UV-Vis spectroscopy unveiled a decrease in band gap energy with increasing deposition temperature, while the Urbach energy, associated with defects and imperfections, exhibited an inverse relationship with band gap and temperature. Experimental current-voltage (I-V) measurements using a Keithley source meter showed variations in the ideality factor with deposition temperature. SCAPS-1D simulations were performed to model the FTO/CZTS interface, incorporating experimental parameters. The simulated I-V behavior demonstrated a transition from recombination to diffusion-dominated current above 1.3 V forward bias. Simulations yielded higher ideality factors due to increased contributions from recombination and diffusion currents. Overall, this study provides insights into the growth, structural, optical, and electrical properties of CZTS thin films deposited by RF sputtering, enabling a comprehensive understanding of the FTO/CZTS heterojunction characteristics and their dependence on deposition temperature.

High responsivity and detectivity β-Ga2O3 solar-blind photodetectors optimized by oxygen vacancy engineering

Solar-blind photodetectors (SBPDs) are core essential components for many critical applications such as precision guidance, fire warning, and space communications. Ultra-wide bandgap semiconductor β-Ga2O3 is considered to be an ideal material for the fabrication of SBPDs. However, synthetizing β-Ga2O3 with high quality factor while simultaneously in situ modulation of electronic and optoelectronic properties to enhance performance has been challenging. Here, pulsed laser deposition (PLD) technology is used to synthesize high-quality β-Ga2O3 thin films on a sapphire substrate. The oxygen vacancy engineered β-Ga2O3 films can achieve in situ precise control of their surface morphology, optical parameters, and optoelectronic properties by simply adjusting the oxygen pressure. Meanwhile, the optimal thickness of the β-Ga2O3 film for the developing high-performance SBPD is ∼221 nm, determined by fitting and analyzing the optical parameters measured by the ellipsometry. Subsequently, the influence of oxygen pressure on the performance of β-Ga2O3 SBPD is thoroughly explored, considering the optimization of electrode size and deposition time. When the oxygen pressure is set to 15 Pa, the β-Ga2O3-based SBPD achieves highly competitive responsivity (R) and detectivity (D*) at 250 nm, with values of 1080 A·W−1 and 1.4 × 1016 cm·W−1·Hz1/2, respectively. Additionally, the noise component of the β-Ga2O3 SBPD is further studied to calibrated the traditional device performance results. This work introduces a simple and straightforward approach to in situ tuning of the optoelectronic properties of β-Ga2O3, which is important for advancing β-Ga2O3 film growth technology and fabricating high-performance photodetectors.

Influence of sulfurization temperature on grain growth in Cu2ZnSnS4 thin films synthesized for solar cell applications

Copper-zinc-tin-sulfur (CZTS) thin films, prepared through a dip-coating solution method, present a highly attractive option as absorber materials for thin-film solar cells. This is due to their affordability, environmentally friendly composition, and abundant availability of raw materials. Although films processed with hydrazine-based solutions have achieved the highest efficiency of approximately 12.6%, the toxic and carcinogenic nature of hydrazine negates these advantages. In the ongoing global research on solution-based processing methods, the size of the grains has emerged as a critical factor in the fabrication of efficient solar cells. In our study, we have successfully prepared CZTS thin films with a pure kesterite phase, characterized by large micro-sized grains, using a dip-coating process with an ethanol-based precursor solution, followed by sulfurization. We investigated how the grain size evolves with varying sulfurization temperatures. Notably, we observed that increasing the temperature led to larger and more uniform grain growth. These results underscore the potential of our approach for the straightforward production of high-quality films with sizable grains, ultimately enhancing their photosensitivity and making them a promising candidate for efficient solar cell applications.

Carbon Nitride Nanosheets as an Adhesive Layer for Stable Growth of Vertically-Ordered Mesoporous Silica Film on a Glassy Carbon Electrode and Their Application for CA15-3 Immunosensor

Carbon Nitride Nanosheets as an Adhesive Layer for Stable Growth of Vertically-Ordered Mesoporous Silica Film on a Glassy Carbon Electrode and Their Application for CA15-3 Immunosensor

Effect of As4 beam equivalent pressure on the growth dynamics of InAs films grown at low temperature on graphene layers

The present study investigates the growth of InAs films at low temperature on graphene synthesized via molecular beam epitaxy, emphasizing the effect of As4 beam equivalent pressure (5.0 × 10⁻6 Torr (low) and 4.5 × 10⁻⁵ (high)) on the growth dynamics. X-ray diffraction, scanning electron microscopy, and atomic force microscopy, along with correlation functions, revealed that monitoring the As4 beam equivalent pressure affects the structural properties of polycrystalline InAs films grown on the graphene/Si layer. The film thickness (particle size) was found to be 172 ± 10 nm and 216 ± 10 nm (40 ± 2 nm and 42 ± 2 nm) for the InAs layers grown at low and high As4 beam equivalent pressure. The increase in the film thickness and particle size with increasing the As4 beam equivalent pressure is attributed to improved material availability and surface kinetics due to the large migration energy of As compared to In and hence the larger diffusion length of In. Conversely, decreasing As4 beam equivalent pressure raises the roughness scaling exponent and enlarges interface width (0.17 µm and 0.31 µm for films grown at high and low As4 beam equivalent pressure) and lateral correlation length, implying smoother surfaces due to larger particles. These insights are pivotal for fabricating advanced semiconductors, underscoring As4 beam equivalent pressure's role in optimizing InAs films for electronic and optoelectronic applications.

Growth Conditions and Interfacial Misfit Array in SnTe (111) Films Grown on InP (111)A Substrates by Molecular Beam Epitaxy.

Tin telluride (SnTe) is an IV-VI semiconductor with a topological crystalline insulator band structure, high thermoelectric performance, and in-plane ferroelectricity. Despite its many applications, there has been little work focused on understanding the growth mechanisms of SnTe thin films. In this manuscript, we investigate the molecular beam epitaxy synthesis of SnTe (111) thin films on InP (111)A substrates. We explore the effect of substrate temperature, Te/Sn flux ratio, and growth rate on the film quality. Using a substrate temperature of 340 °C, a Te/Sn flux ratio of 3, and a growth rate of 0.48 Å/s, fully coalesced and single crystalline SnTe (111) epitaxial layers with X-ray rocking curve full-width-at-half-maxima of 0.09° and root-mean-square surface roughness as low as 0.2 nm have been obtained. Despite the 7.5% lattice mismatch between the SnTe (111) film and the InP (111)A substrate, reciprocal space mapping indicates that the 15 nm SnTe layer is fully relaxed. We show that a periodic interfacial misfit (IMF) dislocation array forms at the SnTe/InP heterointerface, where each IMF dislocation is separated by 14 InP lattice sites/13 SnTe lattice sites, providing rapid strain relaxation and yielding the high quality SnTe layer. This is the first report of an IMF array forming in a rock-salt on zinc-blende material system and at an IV-VI on III-V heterointerface, and highlights the potential for SnTe as a buffer layer for epitaxial telluride film growth. This work represents an important milestone in enabling the heterointegration between IV-VI and III-V semiconductors to create multifunctional devices.

Barrier heights and strong fermi-level pinning at epitaxially grown ferromagnet/ZnO/metal Schottky Interfaces for opto-spintronics applications

Schottky contacts at the ferromagnet/ZnO interface are good candidates for the realization and control of several semiconductor emerging magnetic phenomena such spin injection and spin-controlled photonics. In this work, we demonstrate the epitaxial growth of single-phase and wurtzite-ZnO thin films on fcc Pt/Co0.30Pt0.70 (111) electrodes by molecular beam epitaxy technique. While the magnetic properties of the Pt/Co0.30Pt0.70 buffer remain unchanged after the ZnO growth, the electric measurements of back-to-back Schottky diodes reveal Schottky barrier heights at the metal/ZnO interfaces in the range of 590–690 meV using Cu, Pt and Co0.30Pt0.70 contacts. A pinning factor S and a charge neutrality level (CNL) ΦCNL of 0.08 and 4.94 eV, respectively, are obtained indicating a strong Fermi-level pining with a CNL level that lies 0.64 eV bellow the conductance band of ZnO semiconductor. These experimental findings indicate that Co0.30Pt0.70/ZnO interface follows the metal-induced gap states model and can open a pathway for the realization of opto-spintronics applications such spin-LEDs.

Colloidal Stabilizer‐Mediated Crystal Growth Regulation and Defect Healing for High‐Quality Perovskite Solar Cells

AbstractHigh‐quality perovskite (PVK) films is essential for the fabrication of efficient and stable perovskite solar cells (PSCs). However, unstable colloidal particles in PVK suspensions often hinder the formation of crystalline films with low defect densities. Herein, ethylenediaminetetraacetic acid (EDTA) as a colloidal stabilizer into lead iodide (PbI2) is introduced colloidal solutions. EDTA forms chelated complexes with Pb2+, enhancing the electrostatic repulsion and steric hindrance between colloidal particles. This stabilizes the particles and inhibits disordered motion (Brownian motion) and excessive aggregation. As a result, PbI2 films with a uniform hole distribution are formed, providing ample pathways for subsequent PVK film growth and sufficient space. During the film formation process, the replacement of molecules by formamidinium iodide (FAI) and EDTA slows down crystallization, ultimately leading to PVK films with large grain sizes and low defect density. By using this approach, champion power conversion efficiencies (PCEs) of 24.05% for FA0.97Cs0.03PbI3 PSC, 11.08% for CsPbBr3 PSC, and 25.19% for FA0.945MA0.025Cs0.03Pb(I0.975Br0.025)3 PSC are achieved. Moreover, the EDTA‐based FA0.97Cs0.03PbI3 device retains over 90% of its initial PCE after 1000 h at the maximum power point (MPP) under continuous illumination.

Epitaxial growth of single unit-cell superconducting β-Bi2Pd

Bismuth-based binary alloy β-Bi2Pd has recently been suggested as a connate topological superconductor with immense promise for Majorana zero modes. However, the epitaxial thin films down to the ultimate level of single unit-cell have been challenging. Here, we employed the state-of-the-art molecular beam epitaxy to prepare single unit-cell superconducting β-Bi2Pd films with lateral dimensions of hundreds of nanometers. Utilizing in situ scanning tunneling microscopy/spectroscopy, we uncover evidence of anisotropic superconductivity whose spectra are well fit by anisotropic s-wave gap functions and demonstrate that the epitaxial growth of β-Bi2Pd films relies substantially on the substrate temperature, flux ratio, growth rate, and coverage. The high-quality epitaxial films provide a promising platform to investigate the topological superconductivity at the two-dimensional limit.

Selectable growth and electronic structures of two-dimensional layered InSe and In2Se3 films

Selectable growth and electronic structures of two-dimensional layered InSe and In2Se3 films

Tin-Lead Perovskite Solar Cells with Preferred Crystal Orientation by Buried Interface Approach.

Mixed tin-lead perovskite solar cells (PSCs) have garnered much attention for their ideal bandgap and high environmental research value. However, poly (3,4-ethylenedioxythiophene): poly (styrene sulfonate) (PEDOT: PSS), widely used as a hole transport layer (HTL) for Sn-Pb PSCs, results in unsatisfactory power conversion efficiency (PCE) and long-term stability of PSCs due to its acidity and moisture absorption. A synergistic strategy by incorporating histidine (HIS) into the PEDOT: PSS HTL is applied to simultaneously regulate the nucleation and crystallization of perovskite (PVK). HIS neutralizes the acidity of PEDOT: PSS and enhances conductivity. Especially, the coordination of the C═N and -COO- functional groups in the HIS molecule with Sn2+ and Pb2+ induces vertical growth of PVK film, resulting in the release of residual surface stress. Additionally, this strategy also optimizes the energy level alignment between the perovskite layer and the HTL, which improves charge extraction and transport. With these cooperative effects, the PCE of Sn-Pb PSCs reaches 21.46% (1 sun, AM1.5), maintaining excellent stability under a nitrogen atmosphere. Hence, the buried interface approach exhibits the potential for achieving high-performance and stable Sn-Pb PSCs.

Examination of nonideal film growth in batch atomic layer deposition for plasma-resistant coatings

Atomic layer deposition (ALD) can be used to fabricate protective coatings including moisture barrier layers for organic light emitting diodes, anticorrosion layers for photoelectrodes, and plasma-resistant coating for semiconductor manufacturing equipment, which necessitates the deposition of large and thick ALD films via batch ALD. However, batch ALD for the fabrication of large-area and thick coatings exhibits nonideal film growth, a phenomenon that cannot solely be explained by transient concentration distribution within the deposition chamber. This paper describes the application of precursor “exposure” (in the unit of Langmuir, or Pa s), defined as the integral of concentration over time, as a metric to assess the growth per cycle (GPC) distribution under nonideal ALD conditions, demonstrating that the local GPC correlates well with the cumulative precursor exposure at that site. Consequently, this measure can effectively predict the nonuniformity (NU) distribution of film thickness and facilitate the determination of optimal operating conditions that ensure maximal uniformity of exposure. Under this condition, the intrafilm NU of ALD-grown Al2O3 film (nominal thickness 300 nm) was reduced to 1.2%, and the interfilm NU is diminished to as low as 3.3%. These values represent reductions of 40% and 45%, respectively, compared to the NU levels observed under nonideal conditions (insufficient trimethylaluminum, TMA exposure downstream). The plasma etch rate of ALD-deposited films is merely 4.3 nm/min, representing a reduction of one-half compared to films deposited under nonideal conditions (9.8 nm/min) with overload TMA exposure downstream leading to chemical vapor deposition-like reactions.

A molecular ferroelectric thin film of imidazolium perchlorate on silicon

Molecular ferroelectrics have garnered significant attention due to their structural tunability, low synthesis temperature, and high flexibility. Herein, we successfully synthesized imidazole perchlorate (ImClO4) single crystals and high-quality, highly-oriented thin films on Si substrates. These films demonstrated a high inverse piezoelectric coefficient of 55.7 pm/V. Two types of domain bands were observed: type-I bands tilted ~60° relative to the horizontal axis, and type-II bands positioned perpendicular to the horizontal axis. Under a + 20 V bias, type-I bands showed a reduction and detachment of 180° domain walls to form a needle-like domain. It extended toward the band boundary after applying −20 V bias, which grew along the boundary upon contact. In contrast, type-II bands showed straight domain wall motion and displayed a higher piezoresponse than type-I bands. The growth of high quality molecular ferroelectric thin films on Si substrates paves the way for the development of on-chip devices.