손준우 교수

Electrical resistivity and magnetotransport are explored for thin (3–30 nm), epitaxial LaNiO3 films. Films were grown on three different substrates to obtain LaNiO3 films that are coherently strained, with different signs and magnitude of film strain. It is shown that d-band transport is inhibited as the layers progress from compression to tension. The Hall coefficient is “holelike.” Increasing tensile strain causes the film resistivity to increase, causing strong localization to appear below a

The location and nature of fixed charge states in high-k/GaN metal-oxide-semiconductor capacitor structures are characterized by analyzing flatband voltage shifts in high-frequency capacitance-voltage measurements. It is shown that a significant fixed, positive sheet charge forms at Al2O3/GaN interfaces, but not at HfO2/GaN interfaces. Furthermore, an interface dipole is created at HfO2/Al2O3 interfaces, which causes an abrupt shift in the flat band voltage as HfO2 is introduced to form HfO2/Al2

The resistance of superlattices composed of bilayers of ultrathin (∼4 unit cells) of LaNiO3 and ∼3 unit cells of insulating SrTiO3 is explored as a function of temperature and the number of bilayers. All superlattices with more than one bilayer are metallic, whereas a single bilayer is insulating. Two possible interpretations of the electrical characteristics of the superlattices are discussed. The first model involves conduction in parallel-connected layers, whereas the second model assumes cou

Atomic layer deposition was adopted to deposit VO x thin films using vanadyl tri-isopropoxide {VO[O(C 3 H 7 )] 3, VTIP} and water (H 2 O) at 135 °C. The self-limiting and purge-time-dependent growth behaviors were studied by ex situ ellipsometry to determine the saturated growth conditions for atomic-layer-deposited VO x . The as-deposited films were found to be amorphous. The structural, chemical, and optical properties of the crystalline thin films with controlled phase formation were investig

Abstract The use of gate bias to control electronic phases in VO 2 , an archetypical correlated oxide, offers a powerful method to probe their underlying physics, as well as for the potential to develop novel electronic devices. Up to date, purely electrostatic gating in 3‐terminal devices with correlated channel shows the limited electrostatic gating efficiency due to insufficiently induced carrier density and short electrostatic screening length. Here massive and reversible conductance modulat

Designing energy-efficient artificial synapses with adaptive and programmable electronic signals is essential to effectively mimic synaptic functions for brain-inspired computing systems. Here, we report all-solid-state three-terminal artificial synapses that exploit proton-doped metal–insulator transition in a correlated oxide NdNiO 3 (NNO) channel by proton (H + ) injection/extraction in response to gate voltage. Gate voltage reversibly controls the H + concentration in the NNO channel with fa

The scattering of charge carriers by line defects, i.e., threading dislocations (TDs), severely limits electron mobility in epitaxial semiconductor films grown on dissimilar substrates. The density of TDs needs to be decreased to further enhance electron mobility in lattice-mismatched epitaxial films and heterostructures for application in high-performance electronic devices. Here, we report a strategy for the post-treatment of epitaxial La-doped BaSnO3 (LBSO) films by delicately controlling the

In situ exsolution of metal nanoparticles (NPs) is emerging as an alternative technique to deliver thermally stable and evenly dispersed metal NPs, which exhibit excellent adhesion with conducting perovskite oxide supports. Here we provide the first demonstration that Ni metal NPs with high areal density (similar to 175 mu m(-2)) and fine size (similar to 38.65 nm) are exsolved from an Asite-deficient perovskite stannate support (La0.2Ba0.7Sn0.9Ni0.1O3-delta(LBSNO)). The NPs are strongly anchore

Abstract We report direct evidence that oxygen vacancies affect the structural and electrical parameters in tensile-strained NdNiO 3−δ epitaxial thin films by elaborately adjusting the amount of oxygen deficiency (δ) with changing growth temperature T D . The modulation in tensile strain and T D tended to increase oxygen deficiency (δ) in NdNiO 3−δ thin films; this process relieves tensile strain of the thin film by oxygen vacancy incorporation. The oxygen deficiency is directly correlated with

Ferroelectric photovoltaics (FPVs) have drawn much attention owing to their high stability, environmental safety, and anomalously high photovoltages, coupled with reversibly switchable photovoltaic responses. However, FPVs suffer from extremely low photocurrents, which is primarily due to their wide band gaps. Here, we present a new class of FPVs by demonstrating switchable ferroelectric photovoltaic effects and narrow band-gap properties using hexagonal ferrite (h-RFeO3) thin films, where R den

Electronic phase modulation based on hydrogen insertion/extraction is kinetically limited by the bulk hydrogen diffusion or surface exchange reaction, so slow hydrogen kinetics has been a fundamental challenge to be solved for realizing faster solid-state electrochemical switching devices. Here we accelerate electronic phase modulation that occurs by hydrogen insertion in VO2 through vertically aligned 2D defects induced by symmetry mismatch between epitaxial films and substrates. By using domai

Abstract Programmable optoelectronic devices call for the reversible control of the photocarrier recombination process by in‐gap states in oxide semiconductors. However, previous approaches to produce oxygen vacancies as a source of in‐gap states in oxide semiconductors have hampered the reversible formation of oxygen vacancies and their related phenomena. Here, a new strategy to manipulate the 2D photoconductivity from perovskite stannates is demonstrated by exploiting spatially selective photo

Abstract Heterogeneous interfaces exhibit the unique phenomena by the redistribution of charged species to equilibrate the chemical potentials. Despite recent studies on the electronic charge accumulation across chemically inert interfaces, the systematic research to investigate massive reconfiguration of charged ions has been limited in heterostructures with chemically reacting interfaces so far. Here, we demonstrate that a chemical potential mismatch controls oxygen ionic transport across TiO