Epitaxial films of LaCuOS, a wide gap p-type semiconductor, were grown on yittria- stabi-lized-zirconia (YSZ) (001) or MgO (001) substrates by a reactive solid phase epitaxy (R-SPE) method. Crystal quality, electrical and optical properties on the epitaxial films on each substrate are examined in this paper. Achievement of the heteroepitaxial growth of LaCuOS on the MgO (001) substrate improves optical properties of LaCuOS such as spectral bandwidths and emission intensity, suggesting that the MgO (001) substrate is more preferable than the YSZ (001) for epitaxial growth substrate for LaCuOS.

First-principles calculations are performed for high-K gate dielectric materials using model bulk and interface systems. Detailed electronic structures and atomic configurations are investigated for transition metal (Hf and Zr) oxide, metal doped silicate bulk system and a model Si-silicate interface system. Pseudo polymorphs of metal oxides are investigated to elucidate the underlying driving mechanisms in microscopic configurations of metal oxides and silicates in amorphous structures. We studied energetics and electronic structure of metal oxide pseudo morph with varying oxygen coordination. Dielectric constants of metal oxide and silicate materials are also investigated using the density functional perturbation theory method implemented in the ABINIT code. Electronic and dielectric properties of silica interface layers between high-κ dielectric and Si substrate are investigated leading to a confirmation that 1 nm is the physical limit of gate oxide thickness. Furthermore silica interface layer is found to have small dielectric constant of 3.4∼3.9.

Using density-functional theory with ultrasoft pseudopotentials, we previously investigated the structural and electronic properties of the low-pressure (cubic, tetragonal, and monoclinic) phases of ZrO2 and HfO2, in order to elucidate phonon modes, Born effective charge tensors, and especially the lattice dielectric response in these phases. We now extend this previous work by carrying out similar calculations on the two high-pressure orthorhombic phases, and by providing density-of-states and band-gap information on all polymorphs. Our results show that the electronic structures and dielectric responses are strongly phase-dependent. In particular, the monoclinic phases of ZrO2 and HfO2 are found to have a strongly anisotropic dielectric tensor and a rather small orientational average () compared to the two other low-pressure phases. Our calculations show that is even smaller in the orthorhombic phases.

Interfacial chemistry at indium tin oxide/polymer interfaces is of fundamental importance for the performance of polymer-based light emitting diodes. X-ray photoelectron spectroscopy and Rutherford backscattering spectrometry are used to investigate the stability of the interface formed between indium tin oxide and (i) the light emitting polymer poly(p-phenylenevinylene), and (ii) the hole injecting layer poly(3,4-ethylenedioxythiophene) polystyrenesulfonate. The formed interfaces are not stable and indium-containing species diffuse from the metal oxide surface into the polymer layers.

Photoelectron spectra by X-ray photoelectron spectroscopy (XPS) and UV-photoyield spectroscopy (UV-PYS) have been analyzed to study O2-annealing effects on band diagrams of ferroelectric SrxBiyTa2O9 (SBT) thin films deposited by pulsed laser deposition (PLD) and metalorganic dcecomposition (MOD) methods. XPS studies on the annealed PLD-SBT film has shown a rapid shift in its Bi 4f core peaks from the oxidized to the metallic ones, as the film suffer Ar+ bombardment. Surface of the annealed film has exhibited lower Fermi level than the as-deposited one in UV-PYS. The result suggests O2-annealing can suppress leakage current through PLD-SBT films. The UV-PYS studies on MOD-SBT have shown almost the intrinsic Fermi levels before and after the additional annealing. The XPS studies have shown that the additional annealing is not effective to improve stabilities of (Bi2O2)2+ layers, once the film is baked and crystallized.

In the present study electronic structures of the interface between SBT and transition metal including Au, Ag, Cu, Ni, Pt were studied by employing DV-Xα method. The calculations were performed on cluster models of the interface which were SrTa8O36-M2 (M=Au, Ag, Cu, Ni, Pt, and Bi). The calculations results including Fermi level, bond order, atomic charge distribution shown that there existed significant hybridization between metal d states and the O2p–Ta3d states. The Fermi levels of the metals located in the gap of SBT and metal-induced states, and the position of the Fermi levels did not change greatly due to the different transition metals. The charge of Sr and the transition metal atom transferred to oxygen atom, so that the bonding between Sr (or metal atom) and O was almost ionic bonding. The interactions between transition metal and SBT mainly came from the Coulomb interaction.

Recent progress in the research of ferroelectric-gate FETs is reviewed mainly from a view-point of the data retention characteristics. First, importance of insulator-inserted gate structures such as an MFIS (M; metal, F; ferroelectric, I; insulator, S; semiconductor) or MFMIS structure is described and the necessary conditions for the insulating buffer layer and the ferroelectric film are discussed. Then, experimental results for the SiO2 and high-k dielectric buffer layers combined with such ferroelectric films as SBT (SrBi2Ta 2O9) and BLT ((Bi,La)4Ti3O12) are presented, in which particular attention is paid to the discussion on the induced charge matching between the buffer layer and the ferroelectric film. As an example, it is shown in a Pt/BLT/LaAlO3/Si diode that the high and low capacitance values written by positive and negative pulses can be retained at least for 3 days. Finally, recent experimental results on the data retention characteristics of the ferroelectric-gate FETs are presented.

Thin films of aluminum oxide were deposited on clean Si(100) substrates using trimethylaluminum and oxygen at 300°C. Infrared spectroscopic and x-ray photoelectron spectroscopic analyses of these films showed no aluminum silicate or SiO2 phase formation at the film/substrate interface. The O/Al ratio in the as deposited film was found to be higher than that in stoichiometric Al2O3. On annealing the as deposited samples in Ar at higher temperatures, a peak due to the transverse optical phonon for the Si-O-Si stretching mode appeared in the infrared spectra. A combination of Z-contrast imaging and electron energy loss spectroscopy in the scanning transmission electron microscope confirmed that the annealed samples developed a layer of silicon dioxide at the aluminum oxide-Si interface. Z-contrast images and electron energy loss spectra, obtained while heating the sample inside the scanning transmission electron microscope were used to follow the interfacial SiO2 formation.

Yttria stabilized zirconia (YSZ) and zirconia (ZrO2) thin films without and with Nb-doping were prepared on Si substrate by rf-magnetron sputtering. Undoped YSZ and ZrO2 thin films had (001) orientation, and the orientation was unchanged by the Nb-doping. For both undoped YSZ and ZrO2 thin films, around 2.0 V ion-drift type hysteresis was clearly observed in capacitance-voltage (C-V) characteristics. Nb-doping into YSZ brought about the increase of lattice parameter up to 20 mol% of Nb, which suggests that Nb was incorporated into YSZ lattice up to 20 mol%. By the Nb-doping, the hysteresis in C-V characteristics for YSZ thin film was considerable decreased to around 0.1 V. Drastic suppression of the hysteresis in C-V characteristics was observed for Nb-doped ZrO2 thin film. In this case, the hysteresis was completely disappeared. These facts suggest that oxygen vacancies in YSZ and ZrO2 thin films would be suppressed or disappeared by Nb-doping. This means that Nb is a excellent dopant for both YSZ and ZrO2 to suppress the ion-drift type hysteresis.

Uniformly a-axis-oriented, epitaxially twinned Bi3.25La0.75Ti3O12 (BLT) thin films having the major spontaneous polarization entirely along the film normal were grown by pulsed laser deposition on yttria-stabilized zirconia-buffered Si(100) substrates covered with very thin SrRuO3 bottom electrodes. Using SrRuO3 bottom electrodes of a specific low thickness in combination with a relatively high growth rate and a high oxygen pressure, the volume fraction of the BLT (100) orientation, which is competing with the BLT (118) orientation, was increased up to 99%. In this way the growth of fully a-axis-oriented BLT epitaxial films was achieved, attaining a remanent polarization of 32 mC/cm2. Initial fatigue experiments indicated hardly any fatigue after 109 switching cycles.

Transparent metal-insulator-semiconductor field-effect transistors (MISFETs) were fabricated using a single-crystalline thin film of an n-type transparent oxide semiconductor, a homologous compound InGaO3(ZnO)5, grown by a reactive solid phase epitaxy method. The transparent MISFET exhibited good performances with “normally-off characteristics”, “an on/off current ratio as large as 105” and “insensitivity to visible light”. Field-effect mobility was about 2 cm2(Vs)-1, which is larger than those reported previously for MISFETs fabricated in transparent oxide semiconductors. These improved performance is thought to result from the low defect density and intrinsic-level carrier concentration of the single-crystalline InGaO3(ZnO)5 film.

Interfacial strain and substoichiometric silicon oxides are the two principal causes that result in the redshift of the transverse and longitudinal optical phonons of the asymmetric stretch of O in the Si-O-Si bridging bond of thermal SiO2 with decreasing oxide thickness. Analyses to comprehend these effects, therefore, require consideration of both strain and interfacial substoichiometry. A method to isolate the contributions of strain and suboxide content towards the observed shifts is proposed. The procedure, which utilizes simple optical model and effective medium approximation, allows estimation of the average strain and suboxide concentration in films of different thickness. Analyses of oxides formed at two different temperatures (550 and 700°C) with dry and wet oxygen reveal how process conditions affect the interface properties.

The ability of controlling the growth and interfaces of ultrathin dielectric films on Si and compound semiconductors by ultrahigh vacuum physical vapor deposition has led to comprehensive studies of gate stacks employing the high κ gate oxide Ga2O3(Gd2O3), and the rare earth oxides Gd2O3 and Y2O3. The epitaxy and the interfaces of Gd2O3 on GaAs, GaN, and Si were characterized with atomic precision, and show strong tendency to conform to the underlying substrate, thus providing insight into the fundamental mechanism for low interfacial state density and effective passivation of GaAs and GaN surfaces. These Gd2O3 and Y2O3 gate stacks of abrupt interfaces and controlled microstructures were employed as a model system to elucidate critical issues of materials integration in CMOS scaling.

An amorphous p-type conductive oxide semiconductor was created based on a mother crystalline material, a p-type conductive ZnRh2O4 spinel. The amorphous film of ZnRh2O4 was deposited by an rf sputtering method. Seebeck coefficient was positive, +78 μVK-1, indicating that major carrier is a positive hole. A moderate electrical conductivity (2 S cm-1 at room temperature) for a p-type semiconductor was observed. Optical band gap was estimated to be 2.1 eV. P-n junction diodes with a structure of Au / a-ZnRh2O4 / a-InGaZnO4 / ITO fabricated on glass substrates, operated with a good rectifying characteristics, a rectification current ratio at ± 5V of ∼103. The threshold voltage was 2.1 eV, which corresponds to the band gap energy of the amorphous ZnRh2O4. This is the first discovery of a p-type amorphous oxide and the demonstration of p-n junction all composed of amorphous oxide semiconductors.

Lithium niobate single crystal is an excellent material for various optical applications such as frequency conversion, optical switches, optical modulators and others. An automatic diameter control Czochralski crystals growth system has been designed and fabricated. A brief description of the entire system along with software developed has been described. With optimized growth parameters, pure and Fe/Mn doped crystals have been successfully grown using this system. Preliminary characterizations of these crystals have also been presented.

We have characterized (Sr,Sm)Bi2Ta 2O9 (SSBT) films fabricated by the sol-gel technique on Pt/Ti/SiO2/Si substrates. For ferroelectric-gate FET applications, a ferroelectric film which has a small remanent polarization and a relatively large coercive field is required. It is demonstrated that Sm doping in ferroelectric SBT films is effective to reduce the remanent polarization and enhance the coercive field. Sr0.5Sm0.2Bi2.2Ta2O9 films (150nm) crystallized at 850°C exhibits good electrical properties with a remanent polarization of 1.7 μC/cm2 and a coercive fields of 85 kV/cm. These values are suitable for ferroelectric-gate FET applications.

We have studied the growth of four wide gap insulator materials, CaHfO3, CaZrO3, NdGaO3, and LaGaO3 on SrTiO3. CaHfO3 was selected as the best material for forming the insulator layer of an all-oxide field-effect device because the films had the best crystallinity on SrTiO3 (100) and the highest breakdown field. (La,Sr)TiO3 was selected as a metallic oxide for fabricating the source and drain electrodes. Metallic layers were obtained by depositing ultrathin amorphous LaTiO3 films at room temperature on SrTiO3 and postannealing at high temperature to promote Sr diffusion from the substrate into the film.

The role of the first atomic layers in epitaxial relationship and interface characteristics of SrTiO3 films on CeO2/yttria-stabilized zirconia (YSZ)/Si(001) substrates was investigated. Although SrTiO3 film deposited on CeO2/YSZ/Si directly was preferentially (110)-oriented, epitaxial SrTiO3(001) films could be grown on CeO2/YSZ/Si by controlling first atomic layer of the films. In the case of SrTiO3 film starting from TiO2 layer, the neither ion drift nor charge injection occurred in the SrTiO3/CeO2 interface. On the other hand, for the film starting from SrO layer, an injection-type hysteresis was observed. This is probably due to the electron traps in the interface.

The electrical and structural properties of sputtered indium oxide (In2O3) thin films doped with Mo, Zr, and Ti were studied. Properties of these films are compared to undoped In2O3 and tin-doped In2O3 (ITO). The as-sputtered films, doped with Mo (IO:Mo), exhibited high mobility (45 cm2V-1s-1). Pulsed laser deposition (PLD) was also used to deposit IO:Mo films. The highest mobility achieved for an as-deposited PLD IO:Mo film deposited onto a glass substrate was 42.7 cm2V-1s-1. However, PLD IO:Mo films deposited on single-crystal yttria-stabilized zirconia (YSZ) substrates exhibited a higher mobility of 53.6 cm2V-1s-1 and a greater degree of structural orientation than the sputtered films. Following post-deposition annealing, both the sputtered films on glass, and the PLD films on YSZ, exhibited improved mobilities of 47 and 66 cm2V-1s-1, respectively.

γ-Al2O3-based gas sensing materials were invented, and three kinds of gas sensors, i.e. hydrogen, methane, and alcohol gas sensors, made from these materials were fabricated in our group years ago. Recently, the ether, ethane and gasoline gas sensors have also been made respectively from the nano-powders of γ-Al2O3-based gas sensing materials with different additives. In this paper the sensitivities and selectivites of the three new kinds of the gas sensors are reported, and the effect of the particle size of the nano-powder of the material on the performance of the methane sensors is also studied.