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The effects of reactive gas flow conditions on nonpolar AlN film growth on MnS/Si (100) substrates using reactive DC magnetron sputtering were investigated. During AlN deposition at a substrate temperature of 750 °C, the MnS surface can be unintentionally nitrided, resulting in a decrease in the crystallinity of the AlN. Low-temperature growth of the AlN layer at 300 °C prevents this nitridation and results in the crystallization of nonpolar AlN. A N2 flow equal to 30% of the Ar sputtering gas flow was found to improve the crystallinity of the nonpolar AlN and to reduce nitrogen defects, which play an important role in interfacial reactions. Nitrogen defects promote the formation of alloys such as AlMn and MnSi that degrade the interface and can significantly decompose the MnS. A higher proportion of N2 improves the nonpolar AlN crystallinity, reduces the concentration of defects and suppresses reactions at the AlN/MnS interface.

Research using X-ray diffraction (XRD) remains to be accelerated in spite of its importance in materials science. Automated noise separation or optimization of measurement time in XRD is beneficial for discovering materials. This study analyzes two-dimensional XRD (2D-XRD) with density-based clustering to accelerate XRD. This clustering technique can separate diffraction pattern signals from noises, even with low signal-to-noise ratio (S/N) 2D-XRD. Moreover, we found that the crystalline degree information in composition spreads is captured based on density. This information requires a long time to be captured with conventional one-dimensional detectors or scintillation counters. Therefore, these findings lead to dramatic reduction and optimization of measurement time to improve S/N. The proposed procedure is applicable with 2D detector measurements.

The effect of an Al buffer layer on the growth of AlN on a Si (111) substrate was investigated to develop an all-sputtered GaN film on a Si (111) template substrate. The X-ray diffraction method revealed an obvious improvement in the crystallinity of an AlN layer on the initial layer. At the interface structure, AlN film without the Al buffer layer exhibited surface nitridation of the Si surface, which degraded the AlN crystal growth. After investigating various growth conditions such as substrate temperature and layer thickness, we achieved the all-sputtered epitaxial growth of a GaN/AlN/Si substrate. The substrate temperature was below 650 °C, and the total thickness was less than 200 nm, which is beneficial as regards the cost efficiency of the template substrate for nitride semiconductors.

Thin film growth of Zn x Mn1−x S on a Si (100) substrate by sputtering was investigated for nonpolar AlN film growth on Si (100) substrate. The Zn x Mn1−x S buffer layer reduces the large differences in thermal expansion coefficient and lattice constants between AlN and Si. Although the solubility of ZnS in MnS is less than 5% at 800 °C in bulk form, the insertion of a room-temperature MnS layer between Zn x Mn1−x S and Si enabled (100)-oriented cubic-Zn x Mn1−x S film growth even at x = 9.5%, which is a metastable phase and a phase separation region in bulk form. On the (100)-oriented cubic Zn x Mn1−x S film, nonpolar AlN growth was achieved by sputtering. Furthermore, X-ray photoelectron spectroscopy measurements revealed that the Zn x Mn1−x S film improved the stability of the AlN/Zn x Mn1−x S interface. Zn x Mn1−x S has the potential to enable nonpolar AlN growth on large-diameter Si (100) substrates.

Electronic states and band bending behavior of SnO2 single crystals grown by physical vapor transport were investigated by combining surface-sensitive soft- and bulk-sensitive hard X-ray photoelectron spectroscopy (PES). The as-grown SnO2 crystals had a higher density of in-gap states relating to oxygen vacancies in comparison with the SnO2 crystal annealed at 1100 °C under oxygen atmosphere. Both samples have similar Fermi level pinning at 0.26 eV below the conduction band minimum at the surface and no surface accumulation layer. The estimated carrier density by PES at the surface of the as-grown and annealed SnO2 crystals were 3.2 × 1017 and 3.2 × 1015 cm−3, respectively.

The effects of the N2 gas flow ratio and the substrate self-bias of reactive sputtering on the polarity of AlN film on various planar sapphire substrates were investigated to obtain a non-polar oriented AlN film. On a c-plane sapphire substrate, substrate self-bias enhanced c-plane AlN growth and Al termination at the surface, as confirmed by X-ray diffraction (XRD) and time-of-flight low-energy atom scattering spectroscopy. In addition, the AlN film deposited at an N2 gas:Ar sputtering gas ratio of 14% with substrate self-bias had high crystallinity with an XRD ω-rocking curve of 17 arcsec for the 0002 diffraction. In contrast, the AlN films on a- and r-plane sapphire substrates had semi-polar and non-polar plane orientations, respectively. However, on the a-plane sapphire substrate, the c-plane-orientated AlN phase was also observed, which was increased under substrate self-bias condition and an N2 flow rate below 30%. Preferable conditions for non-polar AlN growth by reactive sputtering were non-substrate self-bias and a high N2 flow rate of 30% or more.

Surface electronic states and band-bending behavior of a melt-grown (111)-plane In2O3 single crystal were investigated using X-ray photoelectron spectroscopy (XPES). The In2O3 single crystal was cleaved under vacuum conditions below 5 × 10−5 Pa, and loaded to a measurement chamber with a vacuum level of approximately 5 × 10−7 Pa. After cleaving, density reduction of in-gap states relating to oxygen vacancies was confirmed. Nevertheless, the cleaved surface had a surface electron accumulation layer with the surface Fermi level pinned at approximately 0.76 eV above the conduction band minimum. The bulk and surface carrier density were estimated as 3.9 × 1017 and 6.0 × 1019 cm−3 respectively by combining the XPES result and the Poisson–Schrodinger solutions. Scanning nonlinear dielectric microscopy indicated a higher carrier density at the (100) surface than that at the (111) surface, suggesting a crystallographic plane dependence which may originate in defects relating to the dipole and surface instability of the In2O3 surface.

The reaction mechanism of ZrO-based metal resists by extreme ultraviolet (EUV) exposure was investigated using hard X-ray photoelectron spectroscopy, near edge X-ray absorption fine structure spectroscopy, and X-ray diffraction. EUV exposure did not affect the amorphous structure of the metal resist. After EUV exposure, the π* states of the C atom and the σ* states of the O atom of the cell molecules were reacted. Moreover, EUV exposure decomposed the carbonyl species of the cell molecules and forms the high oxidation states of ZrO x . Thus, the metal resist reaction occurred with the decomposition of cell molecules and the formation of ZrO2 by EUV exposure.

In this paper deposited materials using focused ion beam-induced chemical vapor deposition (FIB-CVD) in an AuSi alloyed metal source was investigated. Results using Au and Si FIB-CVD were almost the same as those using Ga FIB-CVD. It was suggested that differences in deposited materials among the ions used should be investigated in more detail.

The impact of TiN deposition on thin high-k (HfO2 and HfSiON) films formed on Si substrates was studied using monoenergetic positron beams. For the predeposition sample, the positrons implanted into Si diffuse toward the high-k/Si interface under the influence of the electric field, suggesting the presence of negative charges in the high-k films. After TiN was deposited on HfO2, positive charges were introduced at the TiN/HfO2 interface, which were associated with the incorporation of nitride into HfO2, resulting in the formation of positively charged oxygen vacancies (VOs). From the isochronal annealing experiments for TiN/HfSiON/Si, it was found that positively charged defects (such as VO) were introduced into HfSiON after annealing at 700–900 °C. These defects were introduced by the interaction between TiN and HfSiON, resulting in the formation of polycrystalline TiO2 at the interface. The positively charged defects were annealed out at 1100 °C, but the dielectric properties of HfSiON degraded.

Silicon dangling bonds (Si-DBs) in HfSiOx have been studied using first-principles calculations. Interestingly, our computational result revealed that the Si-DB-related gap state in HfSiOx locates in a much lower energy region than that in SiOx. This is because Hf atoms enhance the ionic character of the HfSiOx film, which in turn induces a positive charge at the Si site. We consider that the low-lying Si-DB level, which is now very near the N 2p state, contributes to the formation of strong Si–N bonds in HfSiON. The lower shift of the Si-DB level upon cation metal inclusion can be useful information not only for improving the electric properties of high-k gate stacks but also for developing prominent silicon–oxide–nitride–oxide–silicon (SONOS) nonvolatile memories where controllability of the charge trap level is a crucial issue.

Typical p-metals show similar effective work functions close to p+ polycrystalline silicon (poly-Si) pinning position irrespective of materials after high-temperature process. We found that this phenomenon can be explained by the modified Vo model taking into account the effect of Si substrate. Oxygen absorption by Si substrate and subsequent electron transfer to metal electrode clearly explain the p-metal Fermi level pinning as well as p+ poly-Si pinning. In addition, unsuppressed Fermi level pinning by insertion of barrier layer at p+ poly-Si/barrier layer/high-k gate stack, which is one of the open issues concerning p+ poly-Si pinning, has the same overall reaction scheme. The modified model also consistently explains this phenomenon.

Epitaxial SrTiO3 (STO) thin films with high electrical properties were grown on Si using ZnS single- and SrS/MnS hetero-buffer layers. STO films on both ZnS-buffered and SrS/MnS-buffered Si showed two growth orientations, (100) and (110). The temperature dependence of the growth orientation for STO films was different for the ZnS single-buffer layer in comparison with the SrS/MnS heterobuffer layers. (100) growth of STO films on SrS/MnS-buffered Si became dominant at high temperatures about 700 ?C, while (100) growth of STO films on ZnS-buffered Si became dominant at a relatively low growth temperature of 550 ?C. STO(100) films on ZnS-buffered and SrS/MnS-buffered Si showed lattice and domain matches for epitaxial relationships with [001]ZnS?[011]STO and SrS[001]?[011]STO, respectively via 45? in-plane rotation of STO films relative to both ZnS and SrS layers. The ZnS buffer layer contained many stacking faults because of the mismatch between ZnS and Si, however, those defects were terminated at the ZnS/STO interface. In contrast, the MnS buffer was very stable against stacking defect formation. Transmission electron microscopy measurements revealed the presence of a disordered region at the ZnS/Si and MnS/Si interfaces. Auger electron spectroscopy and transmission electron microscopy results showed that a good MnS/Si interface at the initial growth stage degraded to a SiS2-x-rich phase during MnS deposition and again into a SiO2-x-rich phase during STO deposition at the high growth temperature of 700 ?C. It was also observed that STO on SrS/MnS-buffered Si showed a markedly high dielectric constant compared with that of STO on ZnS-buffered Si.

Optical and structural properties of an InGaN double-quantum-well (DQW) laser diode (LD) wafer that lased at 450 nm were investigated to discuss an enormous impact of a polarization-induced electric field on the recombination dynamics in InGaN quantum structures. The quantum-well (QW) structure was shown to have the well thickness as thin as approximately 1 nm and InN molar fraction x of approximately 14%. The gross effective electric field in the QW (FQW) was estimated to be 490 kV/cm from the Franz–Keldysh oscillation (FKO) period in the electroreflectance (ER) spectrum, implying that an internal piezoelectric field (Fpiz) of approximately 1.4 MV/cm was cancelled by the pn junction built-in field (Fbi) and Coulomb screening due to carriers in the DQW. The magnitude of FQW can be further weakened by applying reverse bias (VR) on the junction; the decrease in the photoluminescence (PL) lifetime at low temperature measured under VR was explained to be due to a recovery of electron-hole wavefunction overlap for small VR (|VR

GaN films were grown on (La0.29,Sr0.71)(Al0.65,Ta0.35)O3 (LSAT) (111) substrates, the lattice constant of which matched the 3×3 structure of GaN (0001) and the thermal expansion coefficient of which was close to that of GaN, by atmospheric metalorganic chemical vapor deposition. It was found that the surface of LSAT having a perovskite crystal structure was damaged in ambient of NH3 and TMG gas. However, the epitaxial growth of GaN film on the LSAT substrate was achieved by using an AlN blocking layer to prevent the damage by these gases. The crystallographic orientation was evaluated from a phi-scan of 4-cycle X-ray diffraction to be GaN[1100]∥LSAT[110] rotating in plane by 30° against the expected orientation (GaN[2110]∥LSAT[110]). The 30° rotation would be caused by the bond configuration of the surface of the LSAT substrate. The interface structure at the substrate and the threading dislocation in the films were also investigated using a cross-sectional transmission electron microscope.

Using first-principles total-energy calculations within the framework of the density functional theory, we show that nanometer-scale trenches excavated in GaN with (0001) and surfaces cause a variable electrostatic potential difference, which is tunable by controlling the hydrogen coverage of the surfaces. A positive potential difference of 3.53 V is induced between clean (0001) and surfaces in nanotrenches, while a negative potential difference of −5.93 V is induced in nanotrenches with fully hydrogenated surfaces. The value of the potential difference strongly depends on the H coverage of the surfaces. Nanotrenches excavated in GaN with polar surfaces can supply electricity for various nanoscale devices consisting of molecules, clusters, and atoms inserted into the trenches.

The effect of crystallized ZrO2 (ZrO2-seed), amorphous Hf0.43Zr0.57O2 (HZO; HZO-seed), and amorphous Al2O3 (Al2O3-seed) seed layers on the ferroelectricity of HZO films was investigated. The remanent polarization () of a TiN-electroded capacitor with a ZrO2-seed layer was much larger than that of capacitors with a HZO-seed, Al2O3-seed, or no seed layer. Furthermore, the maximum 2P r was exhibited when the thickness of the ZrO2-seed layer was 2 nm. Large grain growth was observed, which satisfied the same lattice pattern between ZrO2 and HZO films, and indicates that the ZrO2 seed layer plays an important role in the nucleation of the HZO film.

The effects of Y and Mn doping into the rutile TiO2 films on a (100) Ge substrate stack structure were investigated by combinatorial synthesis. Composition spread films were fabricated by combinatorial pulsed laser deposition. Regardless of the dopant concentration, the Mn-doped TiO2 film indicated an amorphous structure. In contrast, the Y-doped TiO2 film had a rutile-type crystal structure below an Y concentration of 11.0 at. %. The high Y concentration enhanced the amorphous structure and Ge diffusion into the TiO2 layer. Although both dopants reduced leakage currents, the effect of Y was greater than that of Mn. The post-deposition annealed Y-doped TiO2 indicated an improvement in the leakage current by three orders of magnitude and electron accumulation at a capacitor structure. The Y doping into TiO2 may provide beneficial effects of good interface control and effective dielectric material for Ge-based capacitors.

The Ag2S gap-type atomic switch based "tug of war" device is a promising element for building a new type of CMOS free neuromorphic computer-hardware. Since Ag+ cations are reduced during operation of the device, it was thought that the gap-material should be a n-type polymer. In this study, we revealed that the polymer bithiophene–oligoethyleneoxide (BTOE) doped poly(ethylene oxide) (PEO), which was used as gap-material in the first demonstration of the "tug of war", is a p-type polymer. For this we used impedance spectroscopy and transistor measurements. We elaborate on how the electrochemical processes in the "tug of war" devices could be explained in the case of p-type conductive gap-materials.

The spontaneous polarization effect of ZnO on the thin film growth of pentacene, which is a typical π conjunction organic semiconductor, was investigated. Pentacene thin films were grown on polar ZnO surfaces by ultraslow organic film physical vapor deposition to obtain layer-by-layer growth. X-ray diffraction measurements revealed that pentacene molecules stand upright on polar ZnO surfaces, and that the films consist of two polymorphs, namely, the thin-film and bulk phases. The thin-film phases of pentacene were observed regardless of the polarity of the ZnO substrate at a thickness of less than six molecular layers. However, pentacene on a Zn-polar ZnO substrate gradually changed to the bulk phase unlike that on an O-polar ZnO substrate. Kelvin probe force microscopy measurements revealed that the surface potential of pentacene becomes more positive with increasing pentacene thickness at less than two molecular layers. The variation in the potential of pentacene on the Zn-polar ZnO substrate was larger than that of pentacene on the O-polar ZnO substrate. These findings indicate that the polarity of the semiconductor can control the growth and electronic state of the inorganic/organic semiconductor interface.

The polarity effects of ZnO on the electronic state of a monolayer pentacene/ZnO interface were investigated by X-ray photoelectron spectroscopy (XPS). XPS revealed that the Zn-polar ZnO (Zn-ZnO) strongly depleted electrons in pentacene at the interface. The O-polar ZnO showed greater electron transfer from ZnO to pentacene than Zn-ZnO. The surface potential of pentacene on ZnO was larger than that of bulk pentacene regardless of the ZnO polarity. These findings indicate that the polarity of ZnO has the potential to control the electronic state of the organic/inorganic semiconductor interface.

The electronic states and band bending behavior of melt-grown In2O3 single crystals were investigated by combining surface-sensitive soft- and bulk-sensitive hard-X-ray photoelectron spectroscopies. The as-grown In2O3 crystal had a higher density of in-gap states related to oxygen vacancies than the In2O3 crystal annealed in air at 1000 °C. Nevertheless, the polished surfaces of both samples had surface electron accumulation layers (SEALs) with similar Fermi level pinning energies at the surface. The estimated peak carrier density at the surface of both samples was 1.2 × 1020 cm−3. The SEALs may originate from defects due to surface polishing or adsorbates.

The effect of annealing on implanted Ga of diamond-like carbon (DLC) films on Si substrates fabricated by focused-ion-beam chemical vapor deposition (FIB-CVD) was investigated. Thermal desorption spectroscopy showed two Ga+ peaks at 470 and 630 °C. These temperatures agree with the results of energy-dispersive X-ray diffraction analysis of Ga concentration in the film. Cross-sectional transmission microscopy revealed changes in the structure of the DLC film at each temperature. At approximately 400 °C, the Ga in the film migrated to the surface and desorbed. Above 600 °C, the Si in the DLC layer near the damaged Si substrate interface recrystallized. These results can be applied to enable deliberate control of the mechanical properties of DLC films fabricated by FIB-CVD.

Hafnium (Hf) 4f core-level binding energy shifts caused by Hf–N bond formation in hafnium oxynitride (HfOxNy) have been studied by first-principles calculations. Our computational results clearly showed that the Hf 4f core-level binding energies are reduced by 0.36 and 0.65 eV for Hf–N and N–Hf–N bond formation, respectively. These results are in good agreement with chemical shifts observed in the X-ray photoelectron spectroscopy (XPS) of HfOxNy films deposited on a Si(100) substrate. In the present work, we demonstrate that the first-principles calculation is a useful tool to clarify chemical environments of Hf-based high-k gate dielectrics.

Binary alloy Schottky contacts on ZnO are developed using the combinatorial ion beam deposition system. The compositional fraction of the Schottky binary alloy was continuously changed by the composition spread technique. Pt–Ru alloy composition spreads were deposited as the Schottky metal alloys. It was shown that the compositional fraction of the Schottky binary alloys changed continuously. A Pt–Ru alloy metal film was grown on o-polar ZnO epitaxialy, and its crystal structures changed from the Pt-phase (cubic structure) to the Ru-phase (hexagonal structure) in the Pt–Ru alloy phase diagram. Schottky barrier heights determined by current–voltage measurements increased with increasing Pt content. By combining the ion beam deposition and combinatorial system, the Schottky barrier heights of the Schottky binary alloys have been controlled systematically.

A theoretical investigation has been made of the origin of substantial threshold voltage (Vth) shifts observed in p+poly-Si gate Hf-based metal insulator semiconductor field effect transistors (MISFETs), by focusing on the effect of oxygen vacancy (VO) formation in HfO2. It has been found that VO formation and subsequent electron transfer across the interface definitely causes substantial Vth shifts, especially in p+poly-Si gate MISFETs. Moreover, the theory also systematically reproduces recent experimental reports that large flat band (Vfb) shifts are observed, even in intrinsic poly-Si gates, and that the Vfb shifts exhibit a high dependence on HfSiOx thickness.

The bottom-electrode effect on a Cu/HfO2 stack structure, which is an oxide-based resistive random access memory (ReRAM) structure, and the resistance switching behavior of the structures were investigated by hard X-ray photoelectron spectroscopy and by comparing the Pt and TiN bottom electrodes. In the Pt bottom electrode, a forward bias voltage induced the reduction of the unintentionally oxidized Cu top electrode and the Cu ion migration in the HfO2 layer, resulting in the switching from the high resistivity to the low resistivity at approximately ±1 V. In contrast, the TiN bottom electrode induced the formation of oxygen vacancies in the HfO2 layer and the thick Cu2O layer at the Cu/HfO2 interface, namely, it induced oxygen migration rather than Cu migration. The switching voltage of the Cu/HfO2/TiN structure was twice that of the Cu/HfO2/Pt structure. The switching mechanism in a nanoionic-type ReRAM structure can be controlled by changing the bottom electrode.

Differences between the resistive switching characteristics of Al2O3/TiO2 and TiO2/Al2O3 bilayer structures, fabricated by atomic layer deposition at 200 °C and post-deposition annealing, were studied in Pt bottom electrode (Pt-BE)/insulator/Pt top electrode (Pt-TE) capacitors. The Pt-BE/Al2O3/TiO2/Pt-TE capacitor exhibits stable bipolar resistive switching with an on-resistance/off-resistance ratio of ∼102 controlled by a small voltage of ±0.8 V. The forming process occurs in two steps of breaking of the Al2O3 layer and transfer of oxygen vacancies (VO) into the TiO2 layer. The capacitor showed poor endurance, particularly in the high-resistance state under vacuum conditions. This indicates that the insulating TiO2 layer without VO is not formed near the Al2O3 layer because oxygen cannot be introduced from the exterior. On the other hand, in the Pt-BE/TiO2/Al2O3/Pt-TE capacitor, multilevel resistive switching with several applied voltage-dependent nonvolatile states is observed. The switching mechanism corresponds to the Al2O3 layer’s trapped VO concentration, which is controlled by varying the applied voltage.

The interface stability between electrodes (Pt, TaC, TiC, and RuO2) and a Bi-containing relaxor ferroelectric oxide, BaTiO3–Bi(Mg2/3Nb1/3)O3 (BT–BMN), applied to a high-temperature operational capacitor was investigated by hard X-ray photoelectron spectroscopy. All the electrodes showed electron filling at the Fermi level after annealing at 400 °C. However, Pt and TaC indicated electrical property degradations due to the thick intermediate layer formation and defect formation of the BT–BMN layer relating to the Bi diffusion into the electrodes. In contrast, TiC inhibited the Bi diffusion and did not show any change in the band alignment after annealing. Furthermore, RuO2 eliminated the defect formation in BT–BMN and showed no change in the band alignment although the Bi diffusion was also observed. These results suggest that the TiC/RuO2/BT–BMN stack structure is a potential candidate for the high-temperature operational capacitor.

The deposition conditions of (100) rutile TiO2 grown on p-type (100) Ge substrates by pulsed laser deposition (PLD) were optimized to improve the electrical properties of the TiO2/Ge structure. Increasing the substrate temperature (T sub) enhanced the grain growth, the surface roughness of the film, and Ge diffusion into the TiO2 layer. The growth rate, which was controlled by the laser density in PLD (L d), affected the Ge diffusion. L d of 0.35 J/cm2 (0.37 nm/min) enhanced the Ge diffusion and improved the crystallinity and surface roughness at a temperature of 450 °C, at which GeO x undergoes decomposition and desorption. However, the Ge diffusion into TiO2 degraded the electrical properties. By using the optimized conditions (L d = 0.7 J/cm2 and T sub = 420 °C) with postannealing, the TiO2/Ge structure showed an improvement in the leakage current of 3 orders of magnitude and the capacitance–voltage property characteristics indicated the formation of a p–n junction.

As an alternative contact electrode material to metals, which is necessary for downsized semiconductor devices in 10 nm processes, an intrinsically conducting polymer was studied in terms of its interfacial charge-transfer behavior with an inorganic semiconductor. Polypyrrole as the conducting polymer was formed using an electrochemical technique on an oxide semiconductor and its electronic properties were evaluated using scanning probe microscopy. The experimental results showed that an ohmic contact was observed dynamically at local positions, although a Schottky barrier was expected in the static electronic state over the measurement area. From this research, the conducting polymer was found to be promising as a contact electrode.

We fabricated a Y2O3–ZrO2 film (YZO) on Al2O3 to achieve the field effect passivation with high negative fixed charge densities on p-type Si. The surface recombination velocity was improved down to 30 cm/s after annealing at 400 °C. This improvement can be attributed to the effective fixed charge enhancement while the interface state densities were kept almost constant. A high thermal tolerance of over 600 °C upon inserting a 2-nm-thick ZrO2 layer between the YZO and Al2O3 interface was confirmed. This result showed that the ZrO2 layer acts as a protective barrier to prevent Al and Y interdiffusions. Annealing at a higher temperature of 800 °C resulted in interface degradation and YZO crystallization, which led to the deterioration of the passivation properties.

Magneto-optical spectroscopy of a transparent ferromagnetic semiconductor, anatase TiO2 doped with Co, is carried out at room temperature. A large magneto-optical response with ferromagnetic field dependence is observed throughout from ultraviolet to visible range and increases with increasing Co content or carrier concentration. The magnitude of magnetic circular dichroism (MCD) per unit thickness has a peak around the absorption edge such a huge value of ~10400 deg/cm at 3.57 eV for a 10 mol% Co-doped specimen. Although the results are not sufficient to prove that the ferromagnetism is in the ordinary framework of diluted magnetic semiconductors, the coexistence of Co impurity and mobile carrier is shown to transform the band structure of host TiO2 to generate ferromagnetism.

A growth of the wurtzite (110) AlN thin films on Si(100) with MnS buffer layer was demonstrated for the first time by KrF pulsed excimer laser deposition. The presence of an epitaxial MnS layer on Si(100) substrate was found to affect the orientation of the AlN growth. AlN films was grown epitaxially on the MnS buffer at a substrate temperature higher than 700°C. The AlN/MnS/Si heterostructure is investigated by X-ray diffraction and in situ reflection high-energy electron diffraction. An AlN(110)∥MnS(100)∥Si(100) with in-plane alignment of AlN[0001]∥MnS[010]∥Si[010] and AlN[1100]∥MnS[001]∥Si[001] was observed. This result indicates a possibility of non-polar epitaxial AlN films on Si(100) with an expectation of a new substrate for GaN based optoelectronic devices on silicon.

We have succeeded in rapid optimization of dielectric properties in a combinatorial BaxSr1-xTiO3 film library fabricated on a highly insulating Si substrate. The thin-film library was prepared by using a pulsed-laser molecular beam epitaxy system equipped with a combinatorial mask for controlling compositional (i.e. x in BaxSr1-xTiO3) variations and a temperature-gradient sample holder for obtaining a growth temperature variation along the x and y axis of the substrate, respectively. The dielectric properties of this combinatorial library were mapped by a scanning evanescent microwave probe at a frequency of 2.5 GHz, revealing a strong dependence of permittivity and loss on the composition and on the growth temperature. The optimum permittivity was found in the film with x~0.5 grown at 730°C. From X-ray diffraction analysis, strong correlation was found between the grain orientations and dielectric properties.

The passivation properties and band structures in aluminum oxide (AlOx) deposited by ozone-based atomic layer deposition (ALD) at room temperature on p-type crystalline silicon were investigated by X-ray photoelectron spectroscopy (XPS). The effective carrier lifetime depends on the thickness of AlOx films, since the field effects induced in the films by fixed charges depend on film thickness. The fixed charges are different by two orders of magnitude between films with thicknesses of 10 and 30 nm. At the 30-nm-thick AlOx/Si interface, the completely accumulated band bending of the Si surface was observed. On the other hand, a thin depletion layer was formed at the 10-nm-thick AlOx/Si interface. From the time-dependent XPS measurements, a hole trap was observed toward AlOx, in which trapping centers existed.

Recently, excellent surface passivation has been achieved for both p- and n-type silicon solar cells using AlOx/SiNx:H stacks deposited by atomic layer deposition and plasma-enhanced chemical vapor deposition. However, alternative materials and deposition methods could provide practical options for large-scale manufacturing of commercial solar cells. In this study we demonstrate that AlOx/AlNx stacks fabricated by reactive radio-frequency magnetron sputtering can provide fairly good surface passivation (Smax of ~30 cm/s) regardless of AlOx thickness, which is found to be due to the high negative fixed charge density (Qeff of −2.8 × 1012 cm−2) and moderately low interface trap density (Dit of 2.0 × 1011 eV−1cm−2). The stacks also show fairly good antireflection performance in the visible and near-infrared spectral region. The demonstrated surface passivation and antireflection performance of in situ reactively sputtered AlOx/AlNx stacks make them a promising candidate for a surface-passivating antireflection coating on silicon solar cells.

An interconnect of flexible and foldable devices based on advanced electronics requires high electrical conductivity, flexibility, adhesiveness on a plastic substrate, and efficient productivity. In this study, we investigated the applicability of a conductive polymer/metal composite to the interconnect of flexible devices. By combining an inkjet process and a photochemical reaction, micropatterns of a polypyrrole/silver composite were formed on flexible plastic substrates with an average linewidth of approximately 70 µm within 10 min. The conductivity of the composite was improved to 6.0 × 102 Ω−1cm−1. From these results, it is expected that the conducting polymer/metal composite can be applied to the microwiring of flexible electronic devices.

The preparation of nonpolar ZnO and Cu-doped ZnO thin films on Si substrates was studied for the application to the fabrication of green-light-emitting diodes. The use of rocksalt MnS and wurtzite AlN as buffer layers is a key technology for achieving the heteroepitaxial growth of nonpolar ZnO thin film on a (100) Si substrate. X-ray diffraction and photoluminescence measurements revealed that deposition under a high oxygen partial pressure (~1 Torr) can enhance the nonpolar crystallization of undoped ZnO, and can simultaneously suppress the formation of defects such as oxygen vacancies. These techniques can be also applied to the growth of Cu-doped ZnO. A room-temperature photoluminescence study revealed that nonpolar -oriented Cu-doped ZnO film exhibits enhanced green emission owing to the doped Cu ions.

The Cu ion migration behavior of a Pt/Cu/HfO2/Pt structure, which is an oxide-based resistive random access memory (ReRAM) and exhibits resistance switching behavior at voltages of ±0.8 V, was investigated by hard X-ray photoelectron spectroscopy under a bias operation. A forward bias application, during switching from a high resistive state (HRS) to a low resistive state, reduced the Cu2O bonding state at the interface and the intensity ratio of Cu 2p3/2/Hf 3d5/2 (Cu/Hf) by 23 ± 5%, providing evidence of reductions in unintentionally formed Cu2O and Cu diffusion into the HfO2 layer. After switching to HRS again, Cu/Hf increased by 15 ± 5%, indicating that the Cu ion moved back to the top electrode side, though oxygen showed no bias voltage dependence. Consequently, the Cu ion has a key role in the switching. We directly observed the Cu migration behavior related to the resistive change at the Cu/HfO2 interface under bias operation.

Combinatorial thin-film of (1−x)[BaTiO3]–x[Bi(Mg2/3Nb1/3)O3] — (BT–BMN) was grown on Pt/Ti/SiO2/Si, using pulse laser deposition (PLD) method, by ablating stoichiometric and Bi-10 wt % enriched targets to optimize the Bi content. X-ray photoelectron spectroscopy analysis revealed a linear Bi composition spread. As-deposited films post-annealed at high-temperatures, under oxygen atmosphere, turned into crystalline state. The crystallinity, characterized by X-ray diffraction, is better towards Bi-enriched region. The dielectric constant showed a strong dependency of Bi composition and saturated over Bi-7 wt %. The scanning nonlinear dielectric microscopic investigation revealed ferroelectric phase distribution is better around Bi-7 wt % region where the measured leakage current is also minimum. Dielectric constant over 240 and dielectric constant stability below 13% (25–400 °C range) were obtained.

Floating-gate (FG)-type three-dimensional (3D) fin channel flash memories with triangular fin (TF) and rectangular fin (RF) channels and different interpoly dielectric (IPD) materials have been successfully fabricated using (100)- and (110)-oriented silicon-on-insulator (SOI) wafers and orientation-dependent wet etching. The electrical characteristics of the fabricated FG-type 3D fin channel flash memories including threshold voltage (Vt) variability, program/erase (P/E) speed, memory window, endurance, and data retention at room temperature and 85 °C have been comparatively investigated. A higher P/E speed, a larger memory window, and a lower-voltage operation are experimentally obtained in the TF channel flash memories with an Al2O3–nitride–oxide (ANO) IPD layer (TF-ANO) than in the RF channel ones with the same ANO IPD layer (RF-ANO) and the TF channel ones with an oxide–nitride–oxide (ONO) IPD layer (TF-ONO). The larger memory window and lower-voltage operation of TF-ANO flash memories are due to the high-k effect of the Al2O3 layer and the electric field enhancement at the sharp foot edges of the TF channels. It was also found that data retention for all fabricated FG-type 3D fin channel flash memories shows a weak dependence on temperature.

The epitaxial growth of 0.6[BaTiO3]–0.4[Bi(Mg2/3Nb1/3)O3] (BT–BMN) relaxor ferroelectric thin-films on (100) Nb doped SrTiO3 substrates has been achieved and the structure is investigated for high-temperature capacitor applications. The post growth annealing decreases the oxygen vacancy and other defects in BT–BMN films, resulting in the enhancement of dielectric constant. An insertion of intermediate SrRuO3 layers as an electrode instead of Pt, sandwiching the film, is found to be more effective in enhancing the dielectric constant. A very high dielectric constant exceeding 400 was achieved from high-temperature annealed film and the film showed an excellent dielectric constant stability of below 11% in the temperature range of 80–400 °C. This will enable smaller, high-temperature tolerant, monolithically integrated thin-film capacitors on power semiconductor devices.

Nonpolar a-plane ZnO-film and n-ZnO/i-ZnO/p-GaN heterostructure LEDs were grown epitaxially by pulsed laser deposition and metal?organic chemical vapor deposition on Si(001) using AlN and MnS as buffer layers. X-ray diffraction pole figures showed an epitaxial relationship of ZnO() ? AlN() ? MnS(001) ? Si(001). A near band-edge emission from ZnO was observed at 378 nm in photoluminescence measurements. Electroluminescence of nonpolar n-ZnO/i-ZnO/p-GaN LEDs displayed UV emission at 390 nm under forward and reverse bias. Successful growth of nonpolar n-ZnO/i-ZnO/p-GaN heteroepitaxial on Si provides an attractive solution for integrating nonpolar ZnO-based optoelectronic devices with Si substrates for various applications.

The novel use of metal/polymer composite can be a new candidate for filling through silicon vias (TSV) for three-dimensional (3D) LSI, as it provides a much faster and inexpensive fabrication process compared to copper electroplating. In this study, different process methods have been tested in order to optimize TSV filling with Ag/polypyrrole composite. All together nine method set-ups have been examined to analyse their average filling ratios. The statistical analysis of the techniques showed that the masking and scratching in vacuum environment proved to be the most effective, in average up to 98% filling ratio could be reached within 5 min. The technological differences of the two techniques to remove the additional deposited composite material on the surface caused by the wet dipping in aspect of the resulting via fillings are also detailed in this paper. The use of these techniques can contribute to improve through-put for production of 3D-LSI with metal/polymer composites.

The effects of interface properties such as a negative fixed charge density and an interface trap density on the surface passivation of crystalline Si by O3-based batch ALD AlO x were studied. High-quality surface passivation with S max of ∼10 cm/s was obtained from the AlO x samples deposited at 200 °C after annealing. This feature is attributed to the excellent field effect passivation by the high negative fixed charge density of ∼−5 × 1012 cm−2 and chemical passivation, which reduces the interface trap density to ∼1 × 1011 eV−1 cm−2. The annealed AlO x samples deposited at 200 °C also show high thermal stability during firing at 850 °C. Additionally, we found that the formation of a thin SiO x interlayer is essential for the formation of a high negative fixed charge density that induces strong field effect passivation, and that defect passivation at the Si/SiO x interface by diffused hydrogen from AlO x layers is the origin of chemical passivation.