Search

We demonstrate that the state-of-the-art postirradiation technology for negatively charged oxygen (O−) ions is effective for tailoring carrier concentration (n e ), electrical resistivity (ρ), and optical band gap (E g) in a wide range for polycrystalline 50-nm-thick Sn-doped In2O3 (ITO) films on glass substrates by reactive plasma deposition with direct-current arc discharge. As-deposited ITO films showed n e of 9.2 × 1020 cm−3, ρ of 1.5 × 10−4 Ω cm, and E g of 3.50 eV. The postirradiation of O− ions for 180 min at 250 °C decreased n e to 2.4 × 1018 cm−3. This resulted in a significant increase in ρ to 3.5 × 10−1 Ω cm while retaining the bixbyite crystal structure and the spatial distribution of Sn dopant atoms. The postirradiation of O− ions led to the continuous decrease in the optical E g ranging from 3.50 to 3.02 eV, which is smaller than that of undoped In2O3. For degenerate ITO films, conventional theories about the broadening and narrowing of the optical E g explain the experimental results well. On the other hand, for nondegenerate ITO films, the optical E g shrinkage would be mainly caused by an upward energy shift attributable to the generation of the anti-bonding π* states between O 2p and In 4d orbitals within the topmost valence band owing to the lattice disorder associated with incorporated interstitial oxygen atoms that fill structural vacancy sites. On the basis of the Ioffe–Regel criterion utilizing the electron mean free path, Fermi momentum, and their product, we determined the critical n e at which degenerate ITO films transform to nondegenerate ones.

The loop extrusion theory predicts that the loops of chromosomes are produced by cohesin molecules that uni-directionally extrude a chromatin fiber. We here use an extension of the Rouse model to predict the chain conformational dynamics driven by the loop extrusion process. Our theory predicts that in a bulk solution, the mean square distance between the starting and ending sites of the loop extrusion process decreases with a constant rate. This is because the tension generated by the loop extrusion process drives the displacement of the starting site towards the ending site. In contrast, when the cohesin is entrapped at an interface, the mean square distance does not decrease until the tension generated by the loop extrusion process arrives at the ending site. This theory highlights the fact that the chain dynamics strongly depends on the mobility of the chain segments bound by cohesin., ファイル公開：2020-09-05

Experiments were conducted on Langmuir monolayers composed of chiral dipalmitoyl-phosphatidylcholine (D-DPPC and L-DPPC) molecules and racemic DPPC (dl-DPPC) molecules by Maxwell displacement current (MDC) measurement and Brewster angle microscopy (BAM) to examine the orientational structure and domain shapes of monolayers. The MDCs generated from chiral DPPC monolayers during monolayer compression resembled each other, indicating that the molecular chirality does not have a direct effect on the generation of MDC. The domain shapes of chiral DPPC monolayers depended on the molecular chirality. On the other hand, the MDC generated from racemic DPPC monolayers was different from that generated from chiral DPPC monolayers at the beginning of the pressure plateau, suggesting an effect of molecular chirality. Interestingly, a spanner-like domain shape of racemic DPPC monolayers was discovered. We suggest that phase separation within the domain by monolayer compression is responsible for the formation of this domain shape.

Using an in situ laser absorption and scattering method, the surface roughness and incorporation of In in InGaN layers grown by metal organic vapor-phase epitaxy (MOVPE) were monitored. We observed that the laser light with energy higher than the GaN bandgap was fully absorbed in a GaN layer with a smooth film surface. On the other hand, we observed that the scattering laser light from the surface when the roughness of the InGaN surface increased owing to the formation of In droplets. Laser light with energy lower than the GaN bandgap was weakly absorbed by the GaN layer and was scattered at the back surface of the wafer. Furthermore, laser light intensity decreased during InGaN growth because of In incorporation. The threshold of trimethyl-In (TMIn) for the formation of In droplets as a function of growth temperature was determined using our in situ system. Moreover, we observed that the In droplets were removed by thermal or H2 treatment. The results indicate that multiwavelength laser absorption and scattering enable the optimization of the growth conditions for In-rich InGaN.

We discuss the condition for delocalization of holes in N-doped ZnO, ZnS, and ZnTe. For N-doped ZnO and ZnS, we find large energy reduction due to ionic polarization and a narrow N-impurity band at the top of the valence band compared with those for N-doped ZnTe. These are due to the significant difference between the static and optical dielectric constants of ZnO and ZnS, which have a fair degree of ionic character. We propose a design doping method which involves codoping donors with N acceptors to satisfy the condition for delocalization.

We have developed 100-nm-thick cerium-doped hydrogenated indium oxide (ICO:H) films with a superior Hall mobility of 130–145 cm2 V−1 s−1. The ICO:H films deposited at 150 °C by dc arc-discharge ion plating were post-annealed at 200 °C. The relationship between the Hall mobility and carrier density of the polycrystalline ICO:H films shows that the carrier transport is limited by an ionized impurity scattering mechanism inside the grains. The surfaces of the ICO:H films were found to be very smooth and clear grain-boundary areas were not observed.

Highly transparent conductive Ga-doped ZnO (GZO) films and GZO films with indium codoping (GZO:In) were deposited on glass substrates at 200 °C by ion plating using direct-current arc discharge. Etching in 0.1 wt % HCl solution made it possible to form a craterlike textured surface with a high haze value. For a textured GZO:In film with a remaining thickness of 388 nm, the sheet resistance was 8.1 Ω/□. Damp-heat test results showed that highly moisture-resistant GZO films with a textured surface could be achieved after indium codoping. For the textured GZO:In film, the relative change in sheet resistance was as low as 5.8% while maintaining a high transparency. The moisture-resistant GZO:In films with a textured surface have great potential for use as window layers in thin-film solar cells.

We predict the collapse of a polyelectrolyte brush grafted on an electrode that is induced by applied electric fields for the limiting cases of low and high salt concentrations. The polyelectrolyte brush collapses locally to screen the charges induced on the electrodes. For low salt concentrations, the height of the polyelectrolyte brush decreases steeply with increasing the voltage between the electrodes because the number of counterions expelled from the brush increases exponentially. However, when the system is in equilibrium with monovalent salts at high concentrations, the brush height decreases almost linearly with increasing the voltage instead of the steep collapse. This is because the voltage drop mainly occurs over the diffuse double layer associated with the distant electrode.

Langmuir monolayers of pentadecanoic acid (C15) and dipalmitoyl phosphatidylcholine (DPPC) are investigated in liquid expanded–liquid condensed (LE–LC) phase co-existence region in order to study evolution of circular and undulating LC domains. The Brewster angle microscopy is analyzed to evaluate LC domain size and shape for various average molecular areas. For C15 monolayer circular domain shape and continuous increase of domain size are observed. In contrast, for DPPC monolayer undulating domain shapes are observed, where the mode of oscillations m is quantized depending on the average molecular area. Surprisingly, also the average domain size is quantized and depends on m. These observations are discussed in accordance with the phase rule modified for the monolayer phase co-existence region and observed levels of domain sizes are compared with theories of m-fold distortion.

The electronic structures of molecular beam epitaxy (MBE)-grown GaAs and GaN have been studied by means of a technique using a newly developed surface-insensitive probe, namely, high-resolution hard X-ray (HX) synchrotron radiation (hν= 5.95 keV) photoemission spectroscopy (PES). The obtained valence band spectra and shallow core electronic states are compared with those calculated by the full-potential local density approximation (LDA) calculations explicitly including the Ga 3dcore state. The experimental valence band spectra show a very good match with the calculations, simulated with linear combinations of the partial density of states. The Ga 3dcore ondcore states in GaN indicates a set of fine structures which are attributed to the Ga 3d-N 2shybridization effect. The present experiments indicate that HX-PES provides an indispensable probe for investigating valence band electronic structures of materials, which has so far been impossible due to the limitations of proper surface preparation methods.

We investigated the effects of the incorporation of both Na and O on defect structures for p-type Cu-poor CuInS2 thin films on the basis of the analysis of experimental data using photoluminescence and the secondary ion mass spectrometry and theoretical results obtained by ab-initio electronic band structure calculations. We propose a model of the defect structure for CuInS2 codoped with Na and O. The NaCu and OS form a complex in which they occupy nearest-neighbor sites. The above complex plays an important role in the annihilation of the deep level due to the n-type divacancy which includes Cu vacancies (V Cu) and vacancies of the sulfur close to the V Cu site.

We have investigated the effects of intentional sodium incorporation on the electronic structures and electric properties of Cu-deflcient CuInS2 thin films. From ab-initio electronic band structure calculations, for p-type Cu-deficient CuInS2 films, we find that interstitial Na species, except for Na at Cu sites (NaCu), are very unstable and move easily within the crystal. On the other hand, we find that the formation of the ionic chemical bonds of NaCu-S atoms near the surface are energetically favorable due to a remarkable decrease in Madelung energy compared with that of neutral defects-complex of InCu-2VCu. Those calculated results indicate that controlled Na incorporation into CuInS2 thin films causes a decrease in the concentration of intrinsic donor defects such as InCu and VS, leading to good p-type conductivity of CuInS2 films. Those findings are in good agreement with experiments of electrical conductivity and photoluminescence.

The incorporation of doping elements N and P as well as the impact of these elements on electrical properties of co-evaporated CuInS2 thin films are studied. We show that by using a radical source, nitrogen can be incorporated up to a density of 6×1019 cm-3. N possibly replaces S atoms and should act as an acceptor. An increase in electrical conductivity, however, is not verified. The concentration of P atoms is below the detection limit of 2×1019 cm-3. Hence no clear evidence for phosphorus incorporation is achieved.

We review a new valence control method of codoping for the fabrication of low-resistivity p-type GaN, AlN, ZnSe, ZnO and CuInS2, which is proposed by ab initio electronic structure calculations. We propose the following codoping method (using both n- and p-type reactive dopants at the same time) to fabricate a low-resistivity p-type semiconductors; (1) GaN: [SiGa+2MgGa(or BeGa), H+2MgGa(or BeGa), and ON+2MgGa(or BeGa)], (2) AlN:[ON+2CN], (3) ZnO:[GaZn+2NO, AlZn+2NO and InZn+2NO, (4) ZnSe:[InZn+2NSe, ClSe+2NSe, 2LiZn+ClSe (or ISe), and TeSe+2NSe] and (5) CuInS2:[VCu+InCu+2P]. We compare our predictions of codoping with the recent sucessful codoping experiments for the fabrication of the low-resistivity p-type wide band-gap semiconductors.

We have investigated the electronic structures of Na-incorporated In-rich CuInS2based onab initioelectronic band structure calculations. We find that the formation of ionic NaCu–S bonds decreases the Madelung energy, resulting in a shift in the energy levels of S 3porbitals in the vicinity of the Na atoms towards lower energy regions. Forp-type CuInS2:VCu, we find that interstitial Na species, except for NaCu, are very unstable and move easily within the crystal. This indicates that the mobile Na will act as a passivator of donor states such as InCuand interstitial In.

Current-voltage measurements were performed on Ba1-x K x BiO3/Nb-doped SrTiO3 (BKBO/STO:Nb) all-oxide-type Schottky junctions in the temperature range of 30 to 300 K. The relative permittivity ε r(E, T) of undoped SrTiO3(110) was measured as a function of both temperature and electric field. An anomalous increase in ideality factor n(T) and decrease in zero-bias barrier height Φb0(T) with decreasing temperature were observed and were analyzed using the interfacial layer model with a thin insulating interfacial layer present between metal contact (BKBO) and semiconductor interface (STO:Nb). The increase in n(T) at low temperature can be explained by taking into account the temperature dependence of the permittivity of the depletion layer (STO:Nb). The effect of the electric field dependence of the permittivity of STO:Nb on n(T) is also discussed using an approximate electric field dependence, ε r(T, E)=b/(a+E 2)1/2, where a and b are constants.

We propose the doping of Cl or In species into p-type ZnSe crystals doped with Li, a Zn-substituting species, in order to fabricate low-resistivity p-type ZnSe crystals, based on ab initio electronic band structure calculations. The simultaneous codoping of a Cl or I donor and a Li acceptor enhances Li incorporation in p-type ZnSe crystals due to a strong interaction between donors and acceptors with a decrease in the Madelung energy, resulting in the formation of p-n-p complexes that occupy the nearest-neighbor sites.

On the basis of band-theoretical investigation using the augmented-spherical-wave (ASW) method, we propose a valence-control method, the “codoping method”, to fabricate low-resistivity p-type GaN materials. p-type dopants lead to an increase in the electrostatic energy in GaN materials. This gives rise to destabilization of ionic charge distributions due to a shift of N 2p levels towards higher energy regions. We clarified that codoping of n-type dopants, Si or O atoms, lead to a stable p-type GaN:Mg atom material and investigated differences in the roles of Si and O on the fabrication of low-resistivity p-type GaN materials.

We have studied the electronic structures ofp-type doped CuIn(S0.9375V0.0625)2(V=N, P, As, Sb or Bi) based onab-initioelectronic band structure calculations using the augmented spherical wave (ASW) method. We determined that P and Sb atoms are extremely suitable dopants which can be substituted for S atoms inp-type doped CuInS2crystals with lower resistivity. On the other hand,p-type CuInS2crystals doped with N or Bi had a higher resistivity than those doped with P or Sb.

We have studied the electronic structures of CuIn(S0.875X0.125)2 (X=O, N, P, C, Si or B) based on the ab-initio electronic band structure calculations using the augmented spherical wave (ASW) method. For p-type CuInS2 crystals doped with N, P, C, Si or B, compared with the case of undoped CuInS2, we have found a smaller energy difference between the center of gravity of 3 d bands of Cu close to dopants and that of the outermost p bands of ligands of the Cu atoms. We have clarified the mechanism of dependence of the hybridization between Cu 3 d states and the outermost p states of dopants, X, on the Cu to X bond character (ionic or covalent).

We have studied the influence of intrinsic defects, cation vacancies (V C u , V I n ) and anti-site defects (In C u , Cu I n ), on the bandstructure of nonstoichiometric CuInS2 based upon the ab-initio electronic band-structure calculations using the augmented spherical wave (ASW) method. We have found that an energy shift of the center of gravity of S 3p band is a key parameter for controlling change in the type of conductivity. In p-type crystals (V C u , Cu I n , and V I n ), we have clarified an increase in the strength of the interaction between Cu 3d states and S 3p states caused by a weight shift of the S 3p band towards higher energies in contrast to that in n-type (In C u ).

Quantum effect due to a transverse field Δ in the Sherrington-Kirkpatrick spin.glass model is studied on (i) the phase diagram in the T–Δ plane, and (ii) physical quantities in the spin glass phase. For the latter purpose at T=0, systems with finite number of spins are investigated numerically by mean field approach. A naive mean field theory is examined by the argument on the largest eigenvalue of the random matrix. An attempt is made to improve the mean field calculation.