Realizing the Heteromorphic Superlattice: Repeated Heterolayers of Amorphous Insulator and Polycrystalline Semiconductor with Minimal Interface Defects

An Unconventional Heteromorphic Superlattice (HSL) is Realized, Comprised of Repeated Layers of Different Materials with Differing Morphologies: Semiconducting Pc-In2O3 Layers Interleaved with Insulating A-MoO3 Layers. Originally Proposed by Tsu in 1989, Yet Never Fully Realized, the High Quality of the HSL Heterostructure Demonstrated Here Validates the Intuition of Tsu, Whereby the Flexibility of the Bond Angle in the Amorphous Phase and the Passivation Effect of the Oxide at Interfacial Bonds Serve to Create Smooth, High-Mobility Interfaces. the Alternating Amorphous Layers Prevent Strain Accumulation in the Polycrystalline Layers While Suppressing Defect Propagation Across the HSL. for the HSL with 7:7 Nm Layer Thickness, the Observed Electron Mobility of 71 Cm2 Vs-1, Matches that of the Highest Quality In2O3 Thin Films. the Atomic Structure and Electronic Properties of Crystalline In2O3/amorphous MoO3 Interfaces Are Verified using Ab-Initio Molecular Dynamics Simulations and Hybrid Functional Calculations. This Work Generalizes the Superlattice Concept to an Entirely New Paradigm of Morphological Combinations

Resistance switching behavior of atomic layer deposited SrTiO3_{3} film through possible formation of Sr2_{2}Ti6_{6}O13_{13} or Sr1_{1}Ti11_{11}O20_{20} phases

Identification of microstructural evolution of nanoscale conducting phase, such as conducting filament (CF), in many resistance switching (RS) devices is a crucial factor to unambiguously understand the electrical behaviours of the RS-based electronic devices. Among the diverse RS material systems, oxide-based redox system comprises the major category of these intriguing electronic devices, where the local, along both lateral and vertical directions of thin films, changes in oxygen chemistry has been suggested to be the main RS mechanism. However, there are systems which involve distinctive crystallographic phases as CF; the Magnéli phase in TiO2 is one of the very well-known examples. The current research reports the possible presence of distinctive local conducting phase in atomic layer deposited SrTiO3 RS thin film. The conducting phase was identified through extensive transmission electron microscopy studies, which indicated that oxygen-deficient Sr2Ti6O13 or Sr1Ti11O20 phase was presumably present mainly along the grain boundaries of SrTiO3 after the unipolar set switching in Pt/TiN/SrTiO3/Pt structure. A detailed electrical characterization revealed that the samples showed typical bipolar and complementary RS after the memory cell was unipolar reset

Quantitative Analysis of the Incorporation Behaviors of Sr and Ti Atoms During the Atomic Layer Deposition of SrTiO₃ Thin Films

The atomic layer deposition (ALD) of multication oxide films is complicated because the deposition behaviors of the component oxides are not independent of one another. In this study, the Ti and Sr atom incorporation behaviors during the ALD of SrTiO₃ films were quantitatively examined via the carefully designed ALD process sequences. H₂O and O₃ were adopted as the oxygen sources of the SrO subcycles, whereas only O₃ was used for the TiO₂ ALD subcycles. Apart from the general conjecture on the roles of the different types of oxygen sources, the oxygen source that was adopted for the subcycles of the other component oxide had almost complete control of the metal atom incorporation behaviors. This means that the first half-cycle of ALD played a dominant role in determining the metal incorporation rate, which revealed the critical role of the steric hindrance effect during the metal precursor injection for the ALD rate. O₃ had almost doubled its reactivity toward the Ti and Sr precursors compared with H₂O. Although these are the expected results from the common knowledge on ALD, the quantitative analysis of the incorporation behaviors of each metal atom provided insightful viewpoints for the ALD process of this technically important oxide material. Furthermore, the SrTiO₃ films with a bulk dielectric constant as high as 236 were obtained by the Ru–SrTiO₃–RuO₂ capacitor structure

Enhanced Brightness and Device Lifetime of Quantum Dot Light-Emitting Diodes by Atomic Layer Deposition

Colloidal quantum dot light-emitting diodes (QD-LEDs) are one of the future emissive displays, but understanding charge transport mechanism at the interface and improving charge balances in the device are key challenges to the commercialization of QD-LED. In this study, the ZnO interlayer is introduced by atomic layer deposition (ALD) technique to enhance the performance and lifetime of green-emitting CdZnSeS/ZnS core/shell QD-LEDs. Atomic force microscopy images of QD layer reveal that the thin film of ZnO deposited by ALD reduces the root-mean-square (RMS) roughness of the QD film to less than 2 nm, even though the average diameter of the individual QDs is about 10.9 nm, which results in the suppression of excess electron transport in QD-LED devices. The enhanced performance (an improvement of maximum luminescence from 70 000 to 160 000 cd m(-2)) and operational stability (an improvement of operation lifetime from 20 to 61.5 h at 5000 cd m(-2)) of the QD-LEDs result from the formation of the smoother interface between the QD and electron transport layers, which is indicated by deposition of thicker ALD ZnO or deposition of ALD ZnO after coating the ZnO nanoparticles as an electron transport layer

Plasmon nanogap-enhanced transition temperature of terahertz active device based on superconductors

We present terahertz optical properties of GdBa2Cu3O7-x (GdBCO) superconducting thin films. GdBCO films with a thickness of about 105 nm were grown on a LaAlO3 (LAO) single crystal substrate using a conventional pulsed laser deposition (PLD) technique. Using an Ar ion milling system, the thickness of the GdBCO film was reduced to 58 nm, and its surface was also smoothened. Terahertz (THz) transmission spectra through two different GdBCO films are measured over the range between 0.2 and 1.5 THz using THz time domain spectroscopy. Interestingly, the THz transmission of the thinner GdBCO film has been increased to six times larger than that of the thicker one, while the thinner film is still maintaining its superconducting property at below 90 K. Those thinner superconducting films are suitable to develop various THz applications combined with plasmonic nanostructures to enhance light-matter interactions. Furthermore, this combined system would create opportunities in studying electrodynamics of Cooper pairs inside the limited volume underneath the plasmonic structures and enhancing a transition temperature of the active terahertz switching device based on the superconducting thin films

CsPbBr3 Perovskite Quantum Dot Light-Emitting Diodes Using Atomic Layer Deposited Al2O3 and ZnO Interlayers

Most CsPbBr3 perovskite quantum dot light-emitting diodes (PQD-LEDs) are fabricated with an inverted device structure where hole transport/injection layers are vacuum-deposited on top of ITO/ZnO (as an electron transport layer (ETL))/PQDs. Standard device architecture of PQD-LEDs enables a solution-process of device fabrication; however, the spin-coating of ZnO ETL dissolved in polar solvent results in decreasing photoluminescence (PL) of PQDs because of PQD destabilization in polar medium. Herein, CsPbBr3 PQD-LEDs are fabricated by depositing Al2O3 and ZnO via atomic layer deposition (ALD) to avoid damages originating from the polar solvent during ZnO ETL spin-coating. Low temperature ALD is adopted to prevent the coarsening of the CsPbBr3 PQDs. A thicker Al2O3 interlayer can prevent PL quenching, but an excessively thick interlayer hinders electron transport due to the insulating nature of Al2O3. ZnO is sequentially deposited on Al2O3 interlayer via ALD, and therefore Al2O3/ZnO bilayer structure is used because of its better electron transporting ability and higher power efficiency in PQD-LED devices compared with Al2O3-only devices

Conformal Formation of (GeTe₂)_{(1–<i>x</i>)}(Sb₂Te₃)_<i>x</i> Layers by Atomic Layer Deposition for Nanoscale Phase Change Memories

Phase change random access memory appears to be the strongest candidate for next-generation high density nonvolatile memory. The fabrication of ultrahigh density phase change memory (≫1 Gb) depends heavily on the thin film growth technique for the phase changing chalcogenide material, most typically containing Ge, Sb and Te (Ge–Sb–Te). Atomic layer deposition (ALD) at low temperatures is the most preferred growth method for depositing such complex materials over surfaces possessing extreme topology. In this study, [(CH₃)₃Si]₂Te and stable alkoxy-Ge (Ge­(OCH₃)₄) and alkoxy-Sb (Sb­(OC₂H₅)₃) metal–organic precursors were used to deposit various layers with compositions lying on the GeTe₂–Sb₂Te₃ tie lines at a substrate temperature as low as 70 °C using a thermal ALD process. The adsorption of Ge precursor was proven to be a physisorption type while other precursors showed a chemisorption behavior. However, the adsorption of Ge precursor was still self-regulated, and the facile ALD of the pseudobinary solid solutions with composition (GeTe₂)_(1‑x)(Sb₂Te₃)_<i>x</i> were achieved. This chemistry-specific ALD process was quite robust against process variations, allowing highly conformal, smooth, and reproducible film growth over a contact hole structure with an extreme geometry. The detailed ALD behavior of binary compounds and incorporation behaviors of the binary compounds in pseudobinary solid solutions were studied in detail. This new composition material showed reliable phase change and accompanying resistance switching behavior, which were slightly better than the standard Ge₂Sb₂Te₅ material in the nanoscale. The local chemical environment was similar to that of conventional Ge₂Sb₂Te₅ materials

Nanoscale Characterization of TiO₂ Films Grown by Atomic Layer Deposition on RuO₂ Electrodes

Topography and leakage current maps of TiO₂ films grown by atomic layer deposition on RuO₂ electrodes using either a TiCl₄ or a Ti­(O-i-C₃H₇)₄ precursor were characterized at nanoscale by conductive atomic force microscopy (CAFM). For both films, the leakage current flows mainly through elevated grains and not along grain boundaries. The overall CAFM leakage current is larger and more localized for the TiCl₄-based films (0.63 nm capacitance equivalent oxide thickness, CET) compared to the Ti­(O-i-C₃H₇)₄-based films (0.68 nm CET). Both films have a physical thickness of ∼20 nm. The nanoscale leakage currents are consistent with macroscopic leakage currents from capacitor structures and are correlated with grain characteristics observed by topography maps and transmission electron microscopy as well as with X-ray diffraction