Quality Of Thin Films Research Articles

Low-Frequency Noise Characteristics of Inkjet-Printed Electrolyte-Gated Thin-Film Transistors

Low-frequency noise is a critical characteristic of transistors, but there are only a few experimental works on the noise in printed electronics. In this work, we characterize the low-frequency noise of inkjet-printed electrolyte-gated thin-film transistors (EGTs) with indium-oxide semiconductors. We confirm that the carrier number fluctuation with correlated mobility fluctuation is the dominating noise generation mechanism. Also, we present the benchmark analysis on the noise level of various thin-film technologies. Notably, the extracted value of trap density near the insulator-channel interface is high, indicating an inferior quality of solution-processed and inkjet-printed thin-films. However, because of electrolyte-gating, the large areal gate capacitance compensates the negative effect of the high trap density, effectively reducing the flat-band voltage noise. As a result, the normalized drain current noise is considerably lower than solution-processed transistors and comparable with sputtered inorganic transistors with dielectric gating. This renders the electrolyte-gating approach useful in reducing the noise for printed/solution-based transistors, suitable for low-noise applications.

The precise role of UV exposure time in controlling the orbital transition energies, optical and electrical parameters of thermally vacuum evaporated Se50Te50 thin film

Abstract The scenarios for this work have been summarized in the preparation of the Se50Te50 thin film -(~500 nm)- by thermal evaporation method, then using a mercury lamp with a 150 W/cm2 as a source of ultraviolet radiation. The irradiation process has been carried out in the open air for the Se50Te50 thin film without irradiation and in the UV-treated period between 0.5 and 2.5 h. A thorough study has been carried out which ultimately has been confirmed from it that the irradiation time plays the role of controlling the optical and electrical properties. The energy band type corresponding to the orbital transitions has been determined, and the energies of the orbital transition has been calculated in the Tauc region, HOMO/LUMO gap, and charge transfer gap. In addition to, calculating the exciton and Urbach energies. It has been found that these energies decrease with increasing UV exposure time, except for Urbach's energies, which behave differently. The role of the UV exposure time in controlling many optical constants, dispersion, and dielectric parameters was investigated. Thin-film quality coefficient, the surface resistance, and thermal emission, in addition to the angle of refraction as a function of wavelength, have been determined. As well, the spectral distribution of the molar parameters has been discussed. Finally, the DC electrical conductivity, the activation energy in the extended and hopping state regions, and Mott's parameters have been computed.

Impact of CdCl2 Treatment in CdTe Thin Film Grown on Ultra-Thin Glass Substrate via Close Spaced Sublimation

In this study, close-spaced sublimation (CSS) grown cadmium telluride (CdTe) thin films with good adhesion to 100 µm thin Schott D263T ultra-thin glass (UTG) were investigated. Cadmium chloride (CdCl2) treatment in vacuum ambient was executed to enhance the film quality and optoelectrical properties of CdTe thin film. The post-deposition annealing temperature ranging from 360–420 °C was examined to improve the CdTe film quality on UTG substrate. Various characterization techniques have been used to observe the compositional, morphological, optical, as well as electrical properties. Scanning electron microscopy (SEM) verified that the CdTe morphology and grain size could be controlled via CdCl2 treatment temperature. Energy Dispersive X-Ray Analysis (EDX) results confirmed that the annealing temperature range of 375–390 °C yielded the stoichiometric CdTe films. UV-Vis analysis estimated the post-treatment bandgap energy in the range of 1.39–1.46 eV. Carrier concentration and resistivity were obtained in the order of 1013 cm−3 and 104 Ω-cm, respectively. All the experimental results established that the CdCl2 treatment temperature range of 390–405 °C might be considered as the optimum process temperature for the deposition of CdTe solar cell on UTG substrate in close-spaced sublimation (CSS) method.

Fabrication of Tantalum-Doped Titanium-Oxide Electron-Selective Contacts with High Passivation Quality

In this paper, we report on the fabrication of Ta-doped TiO2 (TiO2:Ta) electron-selective contacts and their improved passivation qualities. By using thermal atomic layer deposition, 3.5 nm-thick, undoped TiO2 films and 3.5 nm-thick TiO2:Ta films with Ta concentrations of 1.5, 2.8, and 5.5 at.% were formed at 150 °C on n-type crystalline silicon substrates with ∼1 nm-thick chemical SiO2 layers. Rutherford backscattering spectroscopic measurements confirmed the Ta concentrations in the films and uniform distributions of Ta atoms in the films. X-ray photoelectron spectrometry measurements implied that Ta atoms rather cause local structural changes than enter substitutionally into Ti sites. After annealing at 130 °C in air, the effective minority carrier lifetime (τ eff) of the TiO2:Ta-passivated samples were significantly higher than those of the samples passivated with undoped TiO2 films. The highest τ eff was obtained for the samples with a relatively low Ta-doping concentration of 1.5 at.%. On the other hand, the passivation quality was degraded by Ta doping with a too high concentration (for example, 18.4 at.%). These results indicate that moderate Ta doping improves the passivation quality of TiO2 thin films.

Trifluoromethylphenylacetic Acid as In Situ Accelerant of Ostwald Ripening for Stable and Efficient Perovskite Solar Cells

Perovskite thin film quality, including large grain size and low defect, is one of the fundamental factors to improve the performance and stability of perovskite solar cells (PSCs). Herein, trifluoromethylphenylacetic acid (TFPA) as the accelerant of Ostwald ripening is introduced and an in situ crystal growth control (ICGC) strategy is developed to obtain high‐quality thin films. With adding a proper amount of TFPA into the FAI/MAX (X is Br and Cl) precursor in the two‐step method, the larger grain size and reduced defect density perovskite are achieved due to Ostwald ripening. The ICGC process makes the average particle size from 476 to 625 nm. The defect density is reduced by a factor of 3.18. The high‐quality thin film endows the champion PSC (SnO2/perovskite/spiro‐OMeTAD) with a power conversion efficiency (PCE) of champion PSC higher than 22.19%. Furthermore, TFPA is insoluble in the water and thus TFPA‐modified film is resistive to moisture. The device can be stored in an argon glove box for 2000 h without efficiency change and when exposed to 65–75% relative humidity for more than 1500 h, it retains more than 85% of the initial PCE.

On the quality of tape-cast thin films of sulfide electrolytes for solid-state batteries

All-solid-state lithium batteries (ASSLBs) have the potential to increase energy density, improve safety, and allow for lower manufacturing costs compared to conventional, liquid-based Li-ion batteries. The thickness of solid electrolyte (SE) layer dictates the cell-level energy density and it is desirable to make the SE layer as thin as possible while maintaining uniformity and defect-free. Manufacturing a high-quality, thin sulfide SE layer at large-scale, however, is challenging. Previous studies have addressed the compatibility of materials used for manufacturing thin sulfide SE films, paving the way for further investigation of processing conditions and film quality. Here we report a strong correlation between the solid loading of dispersions and the quality of tape-casted thin sulfide SE films. We also demonstrate a method for quantifying the quality of thin SE films by observing both pin-hole defects and larger heterogeneous agglomerations of particles in the films. Our thin sulfide SE films containing ∼5 wt% binder are defect-free and show similar ionic conductivity compared to a cold-pressed, binder-free, thick SE pellet, resulting in an ∼11X reduction of area specific resistance. This work on the solid loading of the dispersion used in a scalable tape casting process provides insight for manufacturing high-quality, thin sulfide SE films and to increase the cell-level energy density of ASSLB.

Influence of methyl group in a quinoline moiety on optical and light-induced properties of side-chain azo-polymers

We present the optical and photochromic properties as well as surface quality of thin films of the methacrylic copolymers containing 2-methylquinoline and quinoline azo-dyes in side chain. The extinction coefficient and refractive index were determined using spectroscopic ellipsometry combined with transmittance measurements. Photo-responsive behavior was investigated by determination of trans–cis photoisomerization rates under irradiation with unpolarized 365 nm light. We found that optical properties as well as photoisomerization rates of investigated polymers are dependent on the presence of a methyl substituent in the 2nd position of the quinoline moiety. The quality of the thin films was examined using Atomic Force Microscopy measurements.

Residual solvent extraction via chemical displacement for efficient and stable perovskite solar cells

Solvent residue is inevitable to occur in solution processed thin films, but its influence on the thin film quality has not been identified and addressed to date. Methylammonium acetate (MAAc) ionic liquid has recently been realized as an environmentally friendly solvent for solution processed perovskites. The specific high viscosity, low vapor pressure and strong association with perovskite precursor of the MAAc solvent is a double-edged sword, which endowed an advantageously ambient air operational and anti-solvent free perovskite deposition, but the MAAc is likely to be retained within the film and bring in detrimental effects on device performance of the corresponding solar cells. Herein, we reported a novel route to eliminate the residual solvent via a facial hydrochloric acid (HCl) annealing post-treatment (HAAP). In particular, chemical displacement reaction between the incorporated HCl and residual MAAc can be initiated to form volatile MACl and HAc, efficiently extracting MAAc residue. In the meanwhile, the stimulated mass transport via downward penetration and upward escape can trigger secondary perovskite growth with enlarged grain size and smoothened surface, leading to reduced defect state and improved interfacial contact intimacy, and also partial chloride ions are able to enter the crystal lattice to stabilize perovskite phase structure. As a result, a champion efficiency up to 20.78% originating from enhanced Voc was achieved, and more than 96% of its initial efficiency can be maintained after 1000 h shelf-storage.

Modification of graphene-like, hydrogenated amorphous, hydrogenated tetrahedral amorphous carbon and amorphous carbon thin films by UV-C light

The study aims to explore the effect of low fluence UV-C radiation on the structural quality of thin carbon films. We have modified single to few-layered nano-sized graphene-like films deposited by pulsed laser deposition (PLD) on ~300 nm SiO2/Si substrates and additionally different hydrogenated amorphous carbon a-C:H, tetrahedral amorphous carbon (ta-C:H) and amorphous carbon (a-C) thin carbon films. The modification was carried out by irradiation of the samples with UV-C lamps (Hg lamps λ= 254 nm wavelength and fluence of about 2 × 10−3 W/cm−2) for 5- 30 min in air-atmosphere for graphene-like and up to 60 min for thin carbon films. The irradiated graphene-like films were oriented either at about 2 arcdeg to the impinging light, i.e. the light was almost parallel to the honey-comb plane of graphene film or perpendicular to the UV-C light. The thin carbon films were treated only by a light directed perpendicularly to the films' surface for 60 min. Films were studied before and right after UV-C modification by ellipsometry or profilometry, X-ray photoelectron and Raman spectroscopies to clarify the influence of the UV-C treatment. The most pronounced influence of the UV-C irradiation on the structural quality of the films was established on a-C:H and ta-C:H films where the sp3 and the oxygen-containing radicals content decrease moderately and drops significantly, respectively. The influence of the UV-C irradiation directed almost parallel to the films’ surface on the structural quality of the graphene-like films was slightly higher than that directed perpendicularly. No significant influence on the quality of a-C films synthesized or a-C:H films annealed at high temperatures (1020–1050) °C was observed.

Electrical transport properties of thermally stable n-ZnO/AlN/p-Si diode grown using RF sputtering

The temperature dependent electrical transport properties of n-ZnO/AlN/p-Si heterojunction diode fabricated by RF sputtering system have been investigated over a wide temperature range of 303 K–413 K. The AlN buffer layer in-between ZnO and Si lowers the mismatch in thermal expansion coefficient/lattice constant for improved electrical and structural characteristics. XRD pattern and FESEM confirm the crystalline nature and good quality of ZnO thin film with uniform grain size and crack free structure respectively. As measured from the temperature dependent I–V curve, the apparent barrier height reduces as Ideality factor rises which shows good thermal stability within the temperature range studied here. The mean value of barrier height as well as the Richardson constant have been evaluated. Additionally, by taking into account the Gaussian distribution of inhomogeneous barrier heights, the modified Richardson constant has been estimated.

High-performance methylammonium-free ideal-band-gap perovskite solar cells

Summary The development of mixed tin-lead (Sn-Pb)-based perovskite solar cells (PSCs) with low band gap (1.2–1.4 eV) has become critical not only for pushing single-junction devices toward the maximum efficiency given by the Shockley-Queisser limit, but also for enabling all-perovskite tandem devices beyond this limit. However, achieving high power-conversion efficiency (PCE) and long-term device operation stability simultaneously remains a significant challenge for Sn-Pb-based PSCs. Here, we demonstrate near ideal-band-gap (∼1.34 eV) methylammonium-free Sn-Pb-based PSCs with high efficiency (∼20%) and promising operational stability of maintaining >80% of initial PCE over 750 h under maximum-power-point tracking. The key to this success is the use of a SnCl2⋅3FACl complex additive that improves the microstructure and reduces the development of residual stress in the Sn-Pb perovskite thin films, which in turn enhances the efficiency and stability of the Sn-Pb-based ideal-band-gap PSCs.

Chemical vapour deposition

Chemical vapour deposition (CVD) is a powerful technology for producing high-quality solid thin films and coatings. Although widely used in modern industries, it is continuously being developed as it is adapted to new materials. Today, CVD synthesis is being pushed to new heights with the precise manufacturing of both inorganic thin films of 2D materials and high-purity polymeric thin films that can be conformally deposited on various substrates. In this Primer, an overview of the CVD technique, including instrument construction, process control, material characterization and reproducibility issues, is provided. By taking graphene, 2D transition metal dichalcogenides (TMDs) and polymeric thin films as typical examples, the best practices for experimentation involving substrate pretreatment, high-temperature growth and post-growth processes are presented. Recent advances and scaling-up challenges are also highlighted. By analysing current limitations and optimizations, we also provide insight into possible future directions for the method, including reactor design for high-throughput and low-temperature growth of thin films. This Primer on chemical vapour deposition summarizes current and emerging experimental set-ups as well as common characterization approaches used to determine thin film formation and quality as applied to graphene and other novel 2D materials.

Сравнение характеристик тонких пленок PZT на подложках из сапфира и кремния

The properties of ferroelectric sol-gel PZT films deposited on a silicon-on-sapphire (SOS) substrate are compared with those of PZT films formed on a Si substrate. The crystalline structure, asymmetry of the hysteresis loops, polarization dependences of the transient current, short-circuit photocurrent, and open-circuit photovoltage, as well as the substrate bending have been studied. The PZT on SOS films are textured in a single (111) direction and exhibit symmetric hysteresis loops with a strong remanent polarization. The PZT films on Si are textured in the main (111) and weaker (100) directions, have weaker polarization, and exhibit an asymmetry of the hysteresis loops, which is reflected in the magnitude of the transient current and photocurrent. It is shown that the sapphire substrate has a convex bending that causes a compressive stress in the film plane, which weakens the effect of the lattice mismatch between PZT and Pt. By contrast, the Si substrate has a concave curvature, which causes the film to stretch. The deformations and mechanical stresses within the films were estimated. For PZT on Si, an estimate of the strain gradient along the (111) axis was obtained, which makes it possible to relate the asymmetry of the hysteresis loops to the flexoelectric polarization, with the flexoelectric coefficient for sol-gel PZT films found to be 0.0154 µC/cm. The results obtained show that the sapphire substrate provides a better quality of thin PZT films.

Crystal Structure Visualization of Niobium Nitride (NbN) Thin Film

The well-known program for the visualization and exploration of crystal structural has been by using diamond software. The diffraction technique is used for study the Niobium Thin Film (NbN) and good quality, good resolution powder patterns are recorded in these research work. The calculation of angles by measuring the distance between two atoms, crystal structure visualization and the thin film (NbN) diffraction pattern is main focus in this research work.

Incorporation of Ag into Cu(In,Ga)Se2 films in low-temperature process

Chalcopyrite Cu(In,Ga)Se2 (CIGS) thin films deposited in a low-temperature process (450°C) usually produce fine grains and poor crystallinity. Herein, different Ag treatment processes, which can decrease the melting temperature and enlarge band gap of the CIGS films, were employed to enhance the quality of thin films in a low-temperature deposition process. It is demonstrated that both the Ag precursor and Ag surface treatment process can heighten the crystallinity of CIGS films and the device efficiency. The former is more obvious than the latter. Furthermore, the Urbach energy is also reduced with Ag doping. This work aims to provide a feasible Ag-doping process for the high-quality CIGS films in a low-temperature process.

Improvement in the passivation quality of titanium oxide thin films by doping with tantalum

We demonstrate that the passivation quality of TiO2 electron-selective contacts can be improved by Ta doping. By using atomic layer deposition, 3.5-nm-thick, undoped TiO2 films and Ta-doped TiO2 (TiO2:Ta) films with Ta concentrations of 1.5, 2.8, and 5.5 at.% were formed on n-type crystalline silicon substrates with chemical SiO2 layers. After annealing at 130 °C, the effective minority-carrier lifetime (τeff) of the TiO2:Ta-passivated samples were significantly higher than that of the undoped-TiO2-passivated samples, and the highest τeff was obtained at a relatively low Ta-doping concentration of 1.5 at.%. These indicate that moderate Ta doping improves the passivation quality of TiO2 thin films.

Combination of ultraviolet exposure and thermal post-treatment to obtain high quality HfO2 thin films

The characteristics of HfO2 thin films obtained with and without ultraviolet (UV) exposure post-treatment are discussed. First, 30-nm-thick HfO2 thin films are deposited on silicon wafer substrates using atomic layer deposition followed by a combination of UV exposure and low-temperature thermal post-treatment. Compared with the samples without UV treatment, the HfO2 samples with post-treatment showed a smaller suboxide bond proportion of 2.59%, along with increased crystallinity. The use of a UV-treated gate dielectric HfO2 film in a MOS capacitor device results in lower interface trap and fixed charge densities. Furthermore, the dielectric constant of the HfO2 thin film with the treatment is 22.03, which is higher than that of the film without the treatment, that is, 14.98. In addition, the device capacitance was improved by 56% with the treatment. These results demonstrate the significant potential of the proposed post-treatment process in improving the quality of HfO2 thin films for semiconductor devices.

Zinc oxide incorporated indium tungsten oxide amorphous thin films for thin film transistors applications

Zinc oxide (ZnO), indium tungsten oxide (IWO), and ZnO incorporated indium tungsten oxide (ZIWO) thin films (thickness ~ 10 nm) have been fabricated at room temperature by radio-frequency (RF) magnetron sputtering to study their physical and chemical properties for development of high performance and stable thin film transistors. The study reveals that ZnO incorporation with IWO resulted amorphous, smooth and better quality of thin films in comparison to the zinc oxide and indium tungsten oxide. Furthermore, the fabricated ZIWO thin film transistor exhibits a good device performance with field-effect mobility (μFE) of 26.80 cm2/Vs, threshold voltage (Vth) of 0.62 V, sub-threshold swing (SS) of 0.39 V/decade, and positive biased stress shifting (∆Vth) of +0.82 V than the IWO (conducting in nature) and ZnO (μFE ~ 1.95 cm2/Vs, Vth ~ 14.40 V, SS ~ 1.68 V/decade, ∆Vth of +4.20 V) TFTs counterparts.

Enhancing Efficiency in Transparent Thin‐Film ZnO/P3HT Solar Cells by the Improved Crystalline Quality of ZnO

Face to the suitable ZnO/P3HT heterojunction, improved crystalline quality of zinc oxide (ZnO) thin films is achieved by a simple and effective approach of extending the sputtering time, further the performance of transparent thin‐film solar cells (TFSCs) with P3HT/ZnO heterojunction is greatly enhanced. With extending the sputtering time, the continuous ZnO thin films of necessary thickness is formed on fluorine‐doped tin oxide (FTO) substrate and their crystalline quality is also significantly improved, while the grain size increases and become stable with longer than 60 min. The surface morphology of ZnO thin films with sputtering time of 90 min is smooth. With extending the sputtering time, ZnO thin films show excellent optical property. The improved crystalline quality of ZnO thin films obviously affect the performance of the P3HT‐ZnO SCs, reaching highest fill factor to 0.44, with the sputtering time of 90 min.

Enhancing crystalline/optical quality and electrical properties of the Co-doped ZnS thin films a comparative study

Abstract In this paper, the method of thin film preparation is pulsed laser deposition (PLD). ZnS:Co thin film was grown on sapphire and glass substrates at different temperatures (pressures) by PLD, and we studied a series of optical properties. It shows the crystal structure in XRD. The transmission spectral properties of the ZnS:Co film are very prominent. The transmittance of the film is over 90% between 800 and 6000 nm. The XRD results show the crystalline structure of the film on sapphire substrates and the amorphous structure of the film on glass, which is reflected in the guidance effect of the substrates. The high temperature environment is conducive to the formation of crystals. The best electrical properties of film with 600 °C proposed in the experiment. The research results play a key role in the application of ZnS:Co materials.