Doped Thin Films Research Articles

Donor-Acceptor Type of Fused-Ring Thermally Activated Delayed Fluorescence Compounds Constructed through an Oxygen-Containing Six-Membered Ring.

Nowadays, thermally activated delayed fluorescence (TADF) compounds with a fused-ring core skeleton are getting increasing research interest because of their use in high-performance organic light-emitting diodes (OLEDs). In this study, TADF compounds featuring a D-A-type fused-ring core skeleton are developed. The challenging compatibility of a planarized D-A arrangement and the TADF property is achieved through linking the D and A moieties with two oxygen atoms within a six-membered ring. Compared with a single-oxygen analogue possessing a flexible skeleton and a twisted D-A arrangement, these fused-ring compounds with higher skeleton rigidity show higher photoluminescence quantum yields and narrower emission spectra in toluene and in doped thin films. Their electroluminescent devices achieve high external quantum efficiencies (up to 19.4%), suggesting the potential of rarely achieved D-A-type fused-ring TADF systems to serve as high-performance emitters of OLEDs.

(Edward G. Acheson Award) Exploration of Amorphous Thin Film Electronics

Thin films are critical elements in modern semiconductor devices. They are often prepared in the amorphous phase due to practical reasons, such as the reliability and manufacturability concerns. For example, the amorphous high-k gate dielectric is less prone to current leakage than the polycrystalline dielectric in the MOS device (1). The utilization of amorphous silicon (a-Si:H) or metal oxide semiconductor layer enables the commercial production of thin film transistor (TFT) arrays for flat panel displays (2). Requirements for amorphous thin films are related to the products. For advanced MOSFETs, the nanometer EOT gate dielectric is necessary (3). For LCD or OLED TVs or monitors, the fabrication process has to be low temperature, large area capability, and high throughput (4). In addition, the fabricated device has to be highly reliable, i.e., resistant to damages from subsequent process steps and environmental exposure.In this talk, examples on amorphous thin films conducted in my group will be given and discussed. The doped metal oxide high-k thin film, which has a crystallization temperature higher than that of the undoped film (5), will be examined with respect to fundamental material and electrical properties. Novel devices made from this kind of film, e.g., nanocrystals embedded nonvolatile memories (6) and nano-resistor solid state incandescent LEDs (SSI-LEDs) (7), will be shown and the principles will be deliberated. Separately, PECVD process condition affects the a-Si:H TFT performance as well as the uniformity of the large-area material properties (8), which can be explained with the generalized deposition-etching mechanism (9). Applications of a-Si:H TFTs in nonvolatile memories, e.g., using the floating-gate structure (10), and protein/DNA analysis, e.g., attached with the microchannel device (11), will also be examined.In order to achieve the best device performance with high reliability, both the bulk film and the interface properties of the amorphous thin film have to be tightly controlled, which requires the multidisciplinary approach. This is the early stage of the field. Many new and unique applications of the amorphous thin films can be expected in the near future. Y. Kuo, ECS Trans., 54(1), 273-281 (2013).Y. Kuo, Amorphous Silicon Thin Film Transistors, Kluwer, Norwell, MA, 2004.J. Yan, Y. Kuo, and J. Lu, Electrochem. Solid-State Lett., 10(7), H199-H202 (2007).Y. Kuo, ECS Interface, 22(1), 55-60 (2013).J.-Y. Tewg, Y. Kuo, and J. Lu, Electrochem. Solid-State Lett., 8(1), G27-G29 (2005).Y. Kuo, ECS Trans., 3(3), 253-263 (2006).Y. Kuo and C.-C. Lin, Appl. Phys. Letts., 102(3), 031117 (2013).Y. Kuo, J. Electrochem. Soc., 142, 186-190 (1995).Y. Kuo, Appl. Phys. Lett., 63(2), 144-146 (1993).Y. Kuo and H. Nominanda, Appl. Phys. Letts., 89, 173503 (2006).H. Lee and Y. Kuo, Electrochem. Solid-State Letts., 9, J21-J23 (2006).

Study of electrical conductivity characteristic of tin dioxide films doped with Indium used as gas sensing elements

The electrical conductivity properties were studying characteristics of SnO2:In2O3 thin films, prepared by thermal evaporation method by Magnetron Sputtering Technology with high quality. Optimal conditions for obtaining thin film with maximum gas sensitivity where revealed. During the results of this study was clear that the maximum sensitive degree for doped tin dioxide thin film by Indium at a temperature less than undoped tin dioxide thin films. Sensitivity values were studied for samples with the power of function δ~APβ , where found the value of β decreases from 0.88 for the SnO2 films to 0.32 for the doped films with indium.

Investigation of Vacuum Arc-Deposited ta-C and ta-C:N Thin Films on Silicon and Stainless-Steel Foil Substrates Using Raman Spectroscopy

In this paper, we investigated the vacuum arc-deposited tetrahedral amorphous carbon (ta-C) and nitrogen-doped ta-C (ta-C:N) thin films grown on silicon and stainless-steel foil substrates by the visible Raman Spectroscopy. We found that carbon films grown on silicon surfaces prefer more sp3 hybridized carbon compared to the stainless-steel foil, which prefer more sp2 hybridized carbon even though the films are grown concurrently under the same conditions. The impact energy of plasma ions modifies the interfacial layer formation, giving a strong dependence of the sp2/sp3 ratio with the substrate bias, behaving differently for different substrates. However, nitrogen doping in amorphous carbon thin films helps to increase sp2 contents uniformly on both the surfaces for a fixed substrate bias. Understanding such interfaces are of interest for many electronic, optoelectronic, and energy storage devices as these interfaces get buried and can influence the properties significantly.

The mechanism of phase transition induced by oxygen doping in zirconium nitride thin films

The mechanism of phase transition induced by oxygen doping in zirconium nitride thin films

Sol-Ageing Effect on the Structural and Optical Properties of Undoped and Doped ZrO2 Thin Films

Sol-Ageing Effect on the Structural and Optical Properties of Undoped and Doped ZrO2 Thin Films

Impact of copper doping in NiO thin films deposited by spray pyrolysis on their physical properties

Impact of copper doping in NiO thin films deposited by spray pyrolysis on their physical properties

Rapid synthesis of transparent Lu2O3:RE3+ (RE = Eu, Tb and Tm) thin-film scintillators with tunable RGB luminescence for the detection of X-ray

Developing efficient strategies to fabricate planar photoluminescence scintillators is of great importance to explore X-ray detectors with new platform. Rare-earth (RE) doped Lu2O3 thin films are successfully fabricated by mild aqueous phase electrochemical deposition on ITO/glass substrates with low-temperature post-annealing treatment. The as-prepared Lu2O3:RE3+ (RE = Eu, Tb and Tm) thin films exhibit steerable thickness, high transparency in the visible-NIR range, and low transmittance at UV band mainly due to the oxygen-metal (O2--RE3+) charge transfer processes and the 4f-4f transitions of the RE3+. The Lu2O3:RE3+ thin films emit intense red, green and blue (RGB) photoluminescence, which mainly correspond to the 5D0-7F2 transition of Eu3+, 5D4-7F5 transition of Tb3+ and 1G4-3H6 transition of Tm3+ respectively. Moreover, the transparent Lu2O3:RE3+ thin films also exhibit high sensitivity and linearity luminescence to the X-ray stimulation in a dose rate from 30 to 160 mGy s−1. This rapid and energy-saving synthesis show high efficiency to fabricate rare-earth doped thin-film with a tunable optical performance for optoelectrical application in the fields of solar light concentrators, agricultural light conversion thin films, biosensors, photodetectors and especially the X-ray detectors.

Effect of chalcone moiety on AC conductance of Metal Oxide Nano Composite doped thin polymer film

ABSTRACT PVA, Chitosan, transition metal oxide nanocomposites, and a chlorinated chalcone moiety were used to create a 0.03 cm−1 thin polymer film. Prepared films were characterized using available techniques. The prepared film shows a semi-crystalline nature, proved by XRD analysis, and the nano-scale crystalline size (40–150 nm) was also observed. The surface of the film was smooth and a blooming flower resembling structure appeared in the SEM images obtained at 5 µm. The XPS and EDX spectra reveal the presence of added transition metals and other elements present in the prepared polymer thin film. The prepared film undergoes multistage decomposition upon heating, which was proved by TGA analysis. FT-IR analysis of the film shows that there was no chemical interaction between the added compound and the host polymer; instead, physical interactions alone persisted. Higher AC conductivity was observed with a value of 1.30 × 10−6 Scm−1 at room temperature for polymer composite film made up of MONC and DCHP. This conductance varies with temperature, and at higher temperatures, both dielectric loss and dielectric constant are high. It was discovered that the presence of chalcone moiety improves the AC conductance and dielectric properties of MONC doped polymer composite film.

Electron doping of NdNiO3 thin films using dual chamber CaH2 annealing

Hydrogen donor doping has been exploited as a strategy to manipulate the electronic structure and electrical properties of functional oxide systems. Especially, the development of synthetic methods to achieve electron doping of perovskite rare-earth nickelate thin films utilizing interstitial hydrogen is highly desirable considering the rich electronic phase diagram hosting several functional properties. In this work, we present the hydrogenation of NdNiO3 (NNO) thin films using CaH2 annealing and the resulting giant modulation of electrical resistivity in hydrogenated NNO (H–NNO) thin films. Magnetron sputtering was employed to deposit epitaxial ∼60 ​nm-thin NNO films on single crystal LaAlO3 (LAO) substrates. The formation of the pristine perovskite NNO phase was realized after annealing the films at 500 ​°C for 24 h. CaH2 annealing of NNO thin films for time durations ranging from 1 to 6 ​h was performed in a vacuumed ampule with two interconnected chambers at 280 ​°C. The two-chamber design enables a simple and clean approach for hydrogen doping without physical contact between the powder and sample of interest. X-ray diffraction and Raman spectroscopy revealed the formation of NNO in pristine samples, and the subsequent hydrogen incorporation upon CaH2 annealing without forming any impurity phases. The conversion of the oxidation state of Ni towards +2 upon CaH2 annealing was probed using X-ray photoelectron spectroscopy and X-ray absorption spectroscopy. Consequently, a substantial increase in the room-temperature resistivity was observed upon CaH2 annealing indicating the formation of a strongly correlated electronic configuration of Ni in H–NNO due to electron doping. Overall, the findings of this study highlight the versatility of CaH2 annealing as an electron doping method to tune the electrical properties of correlated oxides at low temperatures.

Lithium activated enhancement in UV-photo response of europium doped ZnO thin film

The advancement in material functionality is an important tool to enhance the sensitivity of ZnO-based UV detectors. The ZnO-based UV detector with different morphology has shown interesting results but the improvement is limited. The incorporation of dopant not only gives the characteristic property of dopant but also tunes electron, hole, and defect concentrations. This work has shown significant improvement in the performance of ZnO-based UV detector with the incorporation of Eu1% and Li1% as the dopants. Sol-gel derived ZnO and Eu 1% doped ZnO (Eu1) and Eu1% Li1% doped ZnO thin film (Eu1Li1) have been investigated for UV detector application. The HRXRD and AFM confirm the high crystalline quality with granular structure in all deposited thin films. The enhanced UV absorption in doped thin film confirms the potentiality of Eu1Li1 thin film as a UV detector. The observed photocurrent value increases twice in Eu1%Li1% doped ZnO thin film (6.75 μA) as compared to pure ZnO (3.14 μA) at 4.0 V bias voltage under UV irradiation of wavelength 325 nm. The responsivity of the Eu1Li1 UV detector is twice as compared to pure ZnO. The enhanced photocurrent is due to an increase of favorable oxygen defect concentration arising with Eu1% and Li1% substitution.

Unfolding the conductivity reversal n- to p-type in phosphorus-doped ZnO thin films by spin-on dopant (SOD) process

Phosphorus doping induced p-type doping in ZnO thin films based on spin-on dopant (SOD) process is reported in this article. Owing to the reduced dependence on the conventional amenities for diffusion/ion-implantation doping, the SOD process provides a simple and cheap doping method. The effect of SOD process temperature on conductivity ZnO thin films is investigated by altering the temperature from 700°C to 1000°C. Systematic field emission scanning electron microscopy analysis demonstrates the impact of doping temperature on the morphological properties of SOD. The x-ray diffraction measurements reveal that the p-type ZnO thin films had (002) preferred crystal orientation. At the same time, x-ray photoelectron spectroscopy validated the formation of the PZn–2VZn complex, which was responsible for the acceptor behaviour of films. Moreover, the photoluminescence spectra tracked down that the origin of 3.35 and 3.31 eV emission peaks is due to the acceptor bound exciton and free-electron to acceptor level transitions, respectively. Finally, an elevated hole concentration of 2.09 × 1016 cm−3 is achieved with a resistivity of 1.14 Ω-cm at 800°C doping temperature. However, the film doped at 900°C and 1000°C showed n-type behaviour due to the generation of high concentration donor defects. Here, we successfully demonstrate that the SOD process has great potential to produce high-quality p-type ZnO thin films suitable for optoelectronic devices applications.

Effect of Al2O3 interlayers on the microstructure and electrical response of ferroelectric doped HfO2 thin films

Novel devices based on ferroelectric hafnium oxide comply with the increasing demand for highly scalable embedded non-volatile memory devices, especially for in-memory computing applications. However, due to the polycrystalline nature of these hafnium oxide films, highly scaled devices face variability concerns. In order to enable smaller grains to circumvent the current limitations, the introduction of Al2O3 interlayers to interrupt the columnar grain growth is presented herein. Transmission Kikuchi diffraction is utilized to investigate influences of the Al2O3 layer on the microstructure of hafnium oxide. Moreover, electrical analysis indicates how the interlayer affects the wake-up phenomena as well as the electric field distribution within the stack. These results provide evidence on how to control grain size, electric behavior, and crystallization temperature by the insertion of Al2O3 interlayers.

Enhanced opto-electronic properties of X-doped (X = Al, Ga, and In) CuO thin films for photodetector applications

Recent trends in optoelectronics still need a highly efficient photodetector based on p-type metal oxide semiconductors. This work stands with the improvement in the performance of CuO thin films via doping with different metals into the thin films. The CuO thin films were successfully doped with 1 wt% of X (X = Al, Ga, and In) by spray pyrolysis method. The prepared doped CuO thin films were characterized to interpret the structural, morphological, and elemental characteristics using advanced techniques. These doped CuO thin films were subjected to study the photodetection ability by analyzing optoelectronic properties. The doping also tuned the optical and electrical properties. Among the fabricated photodetectors, the Al-doped CuO detector shows a maximum photocurrent. The CuO:Al (1.0%) thin film exhibits a high photocurrent of 2.59 × 10−6 A, the responsivity of 2.82 × 10− 1 AW− 1, the external quantum efficiency of 66%, and the detectivity of 1.45 × 1010 Jones. Compared to the other thin films, Al doping has remarkably reduced the bandgap and shows a good photosensing activity that may be due to an increase in charge carriers. These outcomes provide a way to assemble good photodetectors and tune their properties in a wide range.

Process Considerations for selective doping of poly-Si thin films with spin-on dopants and nickel silicide formation for planar thermoelectric devices

The formation of highly doped p-type (boron-doped) and n-type (phosphorus-doped) poly-Si thin films with spin-on dopants on the same wafer poses unique challenges. This work evaluates the pros and cons of different approaches to dopant diffusion, residue removal, and diffusion mask selection when working with spin-on dopants. The experiments have been carried out to optimize the formation of highly doped poly-Si thin films that will form the active layers of a micro-thermoelectric generator (μ-TEG). Building upon previous work on residue removal methods, we report that the residue formation is also dependent on the oxide-silicon surface with a PECVD oxide-Si interface not requiring a post-dopant diffusion nitric acid treatment to achieve a hydrophobic surface. Furthermore, comparing the direct dispense and proximity diffusion methods verifies the existing reports of enhanced diffusion in the latter case. Besides, we observe that doping first with Boron is more conducive than doping first with phosphorus to reduce sheet resistance. We also optimize the contact formation with Ti/Ni thin films and report the mean contact resistivity. Notably, contact annealing precludes the nitric acid treatment requirement even if the surface is hydrophilic after removing dopant residue. Additionally, the sequence of silicidation is observed to be dependent on the doping of the underlying areas.

Absorption and Emission of Chemically and Electrochemically Doped Graphene Nanoribbons

Graphene nanoribbons (GNRs) are narrow stripes of graphene that exhibit unique optical and electronic properties depending on their width and edge type. Recent advances in the bottom-up synthesis of GNRs have enabled precise control over their structure and thus their bandgap. However, the systematic optical and electrical characterization of GNRs obtained from solution-mediated reactions has so far been prevented by the poor stability and processability of GNR dispersions. Here we employ liquid cascade centrifugation (LCC) to obtain size-selected and stable dispersions of bottom-up synthesized 9-aGNRs in toluene and tetrahydrofuran and investigate their intrinsic optical properties. Dispersions and films of these 9-aGNRs show well-defined absorption and photoluminescence bands between 800 and 1000 nm, with relative intensities depending on the LCC-fraction. The best GNR dispersions show photoluminescence quantum yields of up to 70 %. Trions are charged excitons with red-shifted emission that can be created in doped low-dimensional semiconductors, such as carbon nanotubes. Theoretical studies predict large trion binding energies (> 300 meV) in graphene nanoribbons (depending on their width). Hence their optical properties upon doping and possible new features are of interest. Chemical doping of our 9-aGNR dispersions with the strong molecular p-dopant F4-TCNQ and electrochemical doping of GNR thin films in ambipolar electrolyte-gated field-effect transistors results in the expected bleaching of the main absorption bands but also the emergence of new redshifted, charge-induced absorption peaks that may indicate the existence of trions in GNRs.

(Digital Presentation) Characterization of Anisotropic Strain in Anelastic Material By Raman Spectroscopy

Raman spectroscopy has recently been applied for non-destructive characterization of strain in crystalline thin films. It makes use of the numerical value of the mode Grüneisen parameter γ , which equals (minus) the ratio of the relative change in the frequency of a Raman-active vibrational mode and the strain-induced relative change in the unit cell volume. In the presence of in-plane, compressive biaxial strain, aliovalent doped CeO2-films exhibit values of γ which are ~30% smaller than the literature values for the bulk ceramics under isostatic stress. This discrepancy is due in large part to the negative contribution from the anelastic (time-dependent) mechanical properties of oxygen-deficient ceria, thereby raising questions concerning the relationship between Raman mode frequency and anelastic strain. Here we propose a way to "separate" anelastic and elastic contributions to the Grüneisen parameter.500-650nm thick films , x=0.1-0.2, were deposited by RF magnetron sputtering on (100) p-Si wafers (1Ω-cm, tSi=280mm). The films (S-films) were in the fluorite phase with pronounced (111) texture and exhibited biaxial , compressive strain. The in- and out-of-plane lattice parameters (aS || , aS ⊥ ) of the S-films were determined by XRD at different sample tilt angles. The in-plane stress (σbi) in the S-films was determined by profilometry from the change in Si-wafer curvature following film deposition. From σbi and the film biaxial modulus, the elastic component of the in-plane compressive strain (ue ) was calculated (~ -0.2%).Strain-free (relaxed) R-films were obtained by partial substrate removal, forming 2 mm diameter self-supported membranes. Pronounced membrane buckling indicated that residual strain was negligible (aR || ≈ aR ^ ). From the increase in area upon substrate removal, measured with optical profilometry, the total S-film in-plane strain (ut ) was calculated from aS ||/aR-1 ≈ -0.5%. The anelastic strain component may be calculated as ua= ut-ue . The small, anisotropic strain-induced blue shift of the frequency of the F2g -phonon mode for S-films suggests that the F2g mode responds primarily to the elastic component of the strain.As a control, 430nm thick films of mechanically elastic Y2O3 were deposited by sputtering on a Si wafer covered with a 1.5 µm thick PECVD deposited SiO2 layer. This layer supported the Y2O3-films upon membrane formation, but prevented complete strain relaxation. The Y2O3-films were in the double fluorite phase with strong (222) texture and, as with the S-films, were under in-plane compressive strain. The Y2O3 S-film lattice parameters were determined by acquiring XRD-patterns at different sample tilt angles, while membrane in- and out-of-plane lattice parameters were determined with XRD in the transmission and reflection modes, respectively. The values of γ calculated from the Raman frequency of the [Fg +Ag ] peak position were close to the literature values for bulk yttria under isostatic stress.This work should serve as a sample protocol for strain characterization of doped ceria thin films. It supports the concept that the discrepancy between the behavior of Raman modes of isostatically and anisotropically strained doped ceria is related to anelasticity. Our results shed light upon strain characterization by Raman spectroscopy and may lay the foundation for future studies to elucidate selective sensitivity to various strain components.

Orientation-dependent photoluminescence properties of Pr3+ doped Ba0.85Ca0.15Ti0.90Zr0.10O3 thin films

Tuning the photoluminescence properties of rare earth doped ferroelectric thin films is extremely important for developing novel optical-electro devices. Here, the (001), (011) and (111)-oriented Pr3+ doped Ba0.85Ca0.15Ti0.90Zr0.10O3 (BCTZ:Pr3+) epitaxial thin films were prepared on Pb(Mg1/3Nb2/3)O3–PbTiO3 single crystalline substrates by pulsed laser deposition. The effects of crystal orientation on the photoluminescence properties of BCTZ:Pr3+ thin films were systematically investigated. Under the excitation of a 492 nm light, all the films exhibit strong green emission peak around 544 nm, which is ascribed to the transition of 3P0→3H5 of Pr3+ ions. Particularly, the emission intensity strongly depends on the crystal orientation with stronger intensity of (001) (16.76%) and (111)-oriented (19.56%) BCTZ:Pr3+ thin films than that of (011)-oriented one. The dependence of photoluminescence on the orientation can be attributed to different electron-phonon interactions and surface roughnesses. This work provides a novel strategy for the improvement of photoluminescence properties in lanthanides doped ferroelectric films.

Extracting the Complex Refractive Index of an Ultrathin Layer at Terahertz Frequencies With no Prior Knowledge of Substrate Absorption Loss

A method based on complementary transmission and reflection measurements is developed to determine the complex refractive index of an ultrathin layer, despite no knowledge of the substrate's absorption loss. Such a technique avoids error introduced by conventional methods in which the extinction coefficient of the substrate is extracted from a different region of the wafer, or an entirely different reference wafer. This method is implemented to determine the terahertz (THz) complex refractive index of highly doped (i.e., >10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">18</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−3</sup> ) thin films from the emerging group IV semiconductor of GeSn, as well as the THz extinction coefficient of the underlying substrate region.

Nitrogen-doped titanium dioxide films fabricated via magnetron sputtering for vascular stent biocompatibility improvement

Nowadays, vascular stents are commonly used to treat cardiovascular diseases. This article focuses on the influence of nitrogen doping of titanium dioxide thin films, utilized for coating metallic stents to improve their biological properties and biocompatibility. The hereby-investigated titanium oxide thin films are fabricated by magnetron sputtering in a reactive gas atmosphere consisting of argon and oxygen in the first case and argon, nitrogen and oxygen in the second case. Control of the nitrogen and oxygen gas flow rates, and hence their mixing ratios, allows adjustment of the nitrogen-doping level within the titanium dioxide thin films. A correlation of the thin film internal structure on the in vitro behavior of human mesenchymal stem cells derived from adipose tissue is hereby demonstrated. Different nitrogen doping levels affect the surface energy, the wettability, the cell adhesion and thus the cellular proliferation on top of the thin films. The surface colonization of cells on titanium dioxide thin films decreases up to a nitrogen-doping level of ∼ 3.75 at.%, which is associated with a decreasing polar component of the surface energy. For non-doped titanium dioxide thin films, a weak chondrogenesis of adult human adipose-derived mesenchymal stem cells with lower chondrogenic differentiation compared to glass is observed. An increasing nitrogen-doping level leads to linear increase in the chondrogenic differentiation rate, which is comparable to the control value of uncoated glass. Other investigated differentiated cell types do not display this behavior.