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Electrical and optical properties of hydrothermally grown ZnO crystal, as well as structural changes at its surface have been investigated before and after irradiation by pulsed Nd:YAG laser. The spreading resistance measurements have shown a monotonous increase of conductivity by three orders of magnitude when the laser intensity I has been varied from zero to 290 MW/cm2. The PL spectra have revealed an increase of concentration of Zn interstitials at the surface after irradiation by I = 3.5 MW/cm2. Formation of Zn nanoparticles on the crystal surface has been observed at I > 290 MW/cm2. The study of surface structure at I = 315 MW/cm2 has shown that these Zn nanoparticles tend to transform into ZnO nanoparticles after an irradiation by more than 2 laser pulses. A theoretical model of thermal generation and redistribution of point defects has been elaborated to explain the origin of experimentally observed n-type conductivity. According to this model and experimental facts, the n-type conductivity originates from Zn interstitials, which are moved to the crystal surface by large temperature gradient during the laser processing. As a result, Zn-rich surface layer is formed and Zn nanoparticles grow, which are later oxidized into ZnO nanoparticles. We have shown a possibility to control the size distribution of these nanoparticles by choosing appropriate intensity and number of laser pulses.

Zinc oxide (ZnO) nano-rods has widely been investigated as a promising material for photo-catalysis, due to its high photocatalytic activity for the ambient gas molecules. Well-aligned ZnO nano-rods arrays were obtained by the two steps growth. Firstly, seeding layer deposition by RF magnetron sputtering, and secondly, nano-rods growth by hydrothermal processes were investigated. Moreover, after the samples were annealed at 450 °C, these samples were compared in crystalline characteristics and photo-electronic characteristics. The morphology of grown ZnO nano-rods were observed as the hexagonal nano-rods and XRD shows a (002) orientation in wurtzite crystals structure. Annealing processes shows a remarkable improvement of crystallinity. PL measurements showed a steep band edge emission and broad defect states emission and also fairly improvement in crystalline properties by the annealing process. The photoconductivity measurement could lead to investigate the photo-catalytic phenomena on the surface of ZnO nano-rods against the environmental gas molecules. The annealed samples showed a higher photo-conductivity and surface activity for the oxygen gas molecules comparing to the as grown samples.

Hydrogen generation through solar-driven photoelectrolysis of water is a promising technology for clean power supply. Zinc oxide (ZnO) is often applied to a photoelectrochemical (PEC) cells for water splitting, because ZnO has a favorable band edge that straddles the redox potential of photoelectrolysis in water. In addition, formation of ZnO nanostructure is attracting much attention, since the efficiency of PEC cell largely depends on a surface area of contacts. Here we report a modified hydrothermal method to prepare ZnOnanorods, whose structures can be controlled by changing preparation parameters. Our method includes seeding process by simple dip-coating technique, followed by post annealing process and hydrothermal growth process of ZnO nanostructures. The morphology of the grown ZnO depended on the concentration of the solvent used to form the seed layer formation, post-annealing temperature, and growth temperature. At the seed layer solvent concentration of 0.2 M, the ZnOnanorods were needle-like. At 0.9 M, hexagonal ZnOnanorods were obtained. We have successfully prepared hexagonalZnOnanorods by varying seed layer concentration at 0.9M, annealed at 150 °C for 2 h and grown at 120 °C for 1 h.

A laser-induced oxidation method for the formation of a TiO2 layer on a Ti substrate was used. The TiO2 phase can be controlled by an Nd:YAG laser with fundamental frequency at an intensity I = 52.8 MW/cm2 and three different doses. Dose D1 = 3.1x1020 phot/cm2 forms a TiO2 layer in the anatase phase, which possesses the highest photocatalytic, antibacterial and adhesion properties. As the laser dose increases, the TiO2 layer thickness increases from 40 nm to 100 nm, but the photocatalytic decomposition reaction constant decreases. The observed super-linear increase of the TiO2 layer thickness with the laser dose is explained by the presence of positive feedback during the irradiation process. The temperature rises with increasing of the thickness due to the interference-caused decrease of the reflection coefficient. As the thickness increases, TiO2 on Ti structure adhesion decreases from 800 mN to 400 mN due to the formation of a layer with a mixture of phases. The colonization intensities of P. aeruginosa and S. epidermidis bacteria decrease more than tenfold after TiO2 formation. These results are explained by the partial transformation of the TiO2 layer, formed in the anatase phase at dose D1, into the rutile one at doses D2 and D3 due to a deficit of O atoms caused by the low diffusion of O atoms in Ti. According to our experiments and calculations, using the Wagner oxide model, the laser technology can be used to form crystalline structures with a monolayer precision.

The effect of UV Nd:YAG laser intensity on the conductivity and optical properties of hydrothermal ZnO crystal was studied. Three laser intensities characterizing the change of optical, electrical and morphological properties of the crystal have been revealed. The first is improvement of the crystal quality up to I 1 =3.2 MW/cm 2 . The second is at laser intensity higher than I 2 =249.0 MW/cm 2 when the formation of cracks takes place. The third I 3 =290.0 MW/cm 2 leads to the formation of “black ZnO”, which is caused by the emergence of Zn nanoparticles with size around 20 nm. At the same time conductivity of ZnO crystal continues to increase and exceeds the initial value by 277 times. The change of ZnO crystal optical and electrical properties is explained by generation, redistribution and agglomeration of Zn interstitials.

The oxygen plasma immersion ion implantation (O-PIII) method was used to form a TiO2 layer on a Ti substrate. The content of the anatase polycrystalline phase increased from 5.1% to 22.3% of the total TiO2 amount with a higher O+ ion dose. The oxygen ion doses were 3.6 × 1016 ions, 8.1 × 1016 ions, 1.26 × 1017 ions, for 1, 2, and 3 h, respectively, with ion energies of E ≈ 0.8 keV. The polycrystalline phases and morphology of the obtained films were characterized by XRD, FESEM, AFM, and Raman spectroscopy. The chemical bond analysis and layer-by-layer measurements for TiO2 layer thickness evaluation were performed by XPS. The photocatalytic decomposition reaction constants of a methylene blue solution increased from 3.2 × 10−3 min−1 to 4.2 × 10−3 min−1 under UV-A irradiation and the liquid free surface energy increased from 39.0 mJ/m2 to 49.5 mJ/m2 with a higher O-PIII treatment doses. These results were explained by the partial phase transition of the TiO2 layer from rutile to anatase. Thus, the increase in the O+ ions implantation dose into the Ti substrate invoked the reduction of material density from Ti (ρ = 4.506 g/cm3) through TiO2 rutile (4.23 g/cm3) to TiO2 anatase (3.78 g/cm3) phase.

We investigated the effect of processing conditions in low-temperature plasma on luminescent characteristics of A II B VI phosphors. As a result of treatment, the luminescence spectra of all tested phosphors shifted to longer wavelengths, which was caused by change of quantities of luminescent centers due to the redistribution (diffusion) of the activator in the crystal lattice. In the case of ZnS:Cu,Cl and ZnS:Cu,Al phosphors brightness increased as a result of treatment. Therefore when phosphors were plasma coated with protective MgO encapsulation both brightness and stability were improved at the same time.

The direct adsorption mechanism of chlorides (LiCl, NaCl, KCl, CsCl, MgCl 2 , CaCl 2 , SrCl 2 and BaCl 2 ) on carbon nanotubes (CNTs) was investigated with first-principles calculations. The dipole moment, the adsorption energy and the Coulomb interaction energy were calculated. The value of the adsorption energy ranges from 0.2 to 0.6 eV. Considering the structure change of chlorides before and after adsorption, we find that the adsorption energy, just as the Coulomb energy, is proportional to the ratio of chloride’s dipole moment to the square of adsorption distance. So, we conclude that the direct adsorption of chlorides on CNTs occurs mainly through long-range electrostatic interactions.

Carbon nanotube (CNT) yarns have been fabricated by dry spinning from vertically aligned millimeter-long multi-walled carbon nanotube (MWCNT) arrays and their mechanical properties have been studied. By using 2-mm long CNTs and densely packing of CNT yarns we achieved a tensile strength of 1068 MPa and Young’s modulus of 55 GPa. Our CNT yarns have diameters of tens of micrometers being easy to handle and possessing high effective load capacity up to 0.81 N. We discuss mechanical properties of CNT yarns spun from relatively thick MWCNT along with a detailed analysis of various post-spin processes and their effect on CNT yarns characteristics. Also, we point out the difference between mechanical properties of dry spun CNT yarns and conventional spun textile yarns.

We report a low-power-loss and high voltage X-ray tubes with a graphite nanospines (GNS) cold cathode. The cathode is encapsulated in a glass tube having a Beryllium window with a Tantalum film to generate X-rays. The internal tube pressure was below 10 −7 Pa and a tube current exceeding 1 mA at a tube voltage of 22.9 kV was observed in the fabricated X-ray tube. The tube current dispersion, defined as standard deviation/mean ( σ /mean), was relatively small at 2.4%. An X-ray radiation dose rate exceeding 5 Sv/h was obtained from the X-ray tube and the radiation dose rate dispersion was also small ( σ /mean=0.3%). As an application of the X-ray tube, we demonstrated radiography for the rapid inspection of organic products.

A CdTe detector with a Gd converter has been developed and investigated as a neutron detector for neutron imaging. The fabricated Gd/CdTe detector with the 25 μm thick Gd was designed on the basis of simulation results of thermal neutron detection efficiency and spatial resolution. The energy resolution of the Gd/CdTe detector is less than 4 keV, which is enough to discriminate neutron capture gamma rays from background gamma emission. The Gd/CdTe detector shows the detection of neutron capture gamma ray emission in the 155 Gd(n, γ) 156 Gd, 157 Gd(n, γ) 158 Gd and 113 Cd(n, γ) 114 Cd reactions and characteristic X-ray emissions due to conversion-electrons generated inside the Gd film. The observed efficient thermal neutron detection with the Gd/CdTe detector shows its promise in neutron radiography application.

We fabricated large-scale anisotropic carbon nanotube (CNT) paper sheets by stacking long-lasting multiwalled CNT (MWCNT) webs without using binder materials. The MWCNTs are highly aligned in the webs and they retain their alignment in the fabricated paper. Although MWCNTs are just connected by van der Waals force, tensile strength is as strong as 75.6 MPa. In addition, resistivity and thermal conductivity is as good as 2.5 × 10−3 Ω cm and 70 W/m K, respectively. The present high anisotropy ratios of 7.3 in resistivity and of 8.1 in thermal conductivity are due to the high alignment of the ultra-long MWCNTs which have lengths of millimeters. High-speed web drawing with a draw speed of over 10 m/s enables very rapid fabrication. The material properties of CNT structures can be measured by conventional methods for macroscopic samples rather than methods designed for nanomaterials. CNT web technology will enable CNTs to be used in new applications.

Nitrogen-doped (N-doped) p-type ZnTe films and ZnTe–ZnSe superlattices (SLs) were prepared on GaAs (1 0 0) substrates by hot wall epitaxy (HWE) using NH 3 gas and Zn 3 N 2 as a codoping source. We have investigated the compensation effect of Zn 3 N 2 and optimized the growth conditions. Then the nitrogen-doped ZnTe films and ZnTe–ZnSe superlattices of high crystal quality with a high hole concentration were obtained.

The paper describes emission characteristics of semiconductor cold cathodes such as Si-field emitters and metal-oxide-semiconductor (MOS) electron tunneling emitters, and shows that their characteristics reflect the semiconductor property or the electron transport in an incorporated semiconductor device. The paper also describes Smith–Purcell radiation experiment as one of the device applications of semiconductor field emitters.

Europium activated strontium thiogallate (SrGa2S4:Eu) phosphors were prepared by the deposition of SrS:Ga2S3:Eu films of about 1 μm thickness onto quartz glass substrates by two electron beam (EB) evaporation followed by irradiation with 900 keV accelerated electrons and subsequent annealing in either sulfur vapor or H2S(10%):Ar(90%) mixture at 900 °С. Annealing in vaporized sulfur provides a significantly higher crystallinity and PL intensity of the obtained phosphor films in comparison with annealing in H2S:Ar mixture. Preliminary irradiation is found to further increase the crystallinity and photoluminescence (PL) intensity of the subsequently annealed phosphors due to the formation of crystallization centers.

The paper proposes the concept of the compact free electron laser using Smith–Purcell radiation and field emitters, and describes preliminary experiments associated with the generation of a modulation beam directly from the cathodes. The emission characteristics of the GaAs emitter designed for the Gunn effect strongly suggest the generation of a modulation beam. The illumination of a pulse laser on a p-type emitter also generates a modulation beam. However, for a high-frequency modulation beam, the suppression of the diffusion of the photogenerated carriers in the emitter is necessary.

Enhancement of electron emission by illumination of gated field-emitters was studied using a 100 mW cw YAG laser at a wavelength of 532 nm, intensities up to 10 7 W/m 2 and mechanically chopped with a rise time of 4 μs. When shining an array of 640 silicon emitters, the emission current responded quickly to on–off of the laser. The increase of the emission current was proportional to the basic emission current at low gate voltages, but it was saturated at ≈3 μA as the basic current approached 100 μA with the increase of gate voltage. The emission increase was proportional to the square root of laser power at low gate voltages and to the laser power at elevated gate voltages. For 1- and 3-tip silicon emitters, the rise and fall of the current due to on–off of the laser showed a significant time lag. The magnitude of emission increase was independent of the position of laser spot on the emitter base and reached 2 μA at a basic current of 5 μA without showing signs of saturation. The mechanisms of these phenomena are discussed.

We report on the photoluminescence and carrier-transport properties of a GaAs(6.2 nm)/AlAs(1.7 nm) superlattice embedded in a p–i–n diode structure from the viewpoint of the intersubband scattering under an applied bias voltage (electric field). We have found the enhancement of the photoluminescence intensity in the reverse-bias region from 4 to 16 V, accompanying a dip structure. The transient photocurrent simultaneously exhibits delayed-transport profiles in the above bias region. The calculated results of the energies of the Γ1, Γ2 and X1 subbands indicate that the electron scattering between the Γ and the X subbands causes the above experimental results.

We have investigated the electric-field effects on the cw and time-resolved photoluminescence (PL) properties in a marginal type-I GaAs/AlAs superlattice (SL) whose lowest X state (X1) is situated in the lowest Γ(Γ1) miniband. In the low bias voltage regime, the PL spectra reveal the transition between type-I and type-II radiative recombination processes caused by Wannier–Stark localization. In contrast, in the high bias voltage regime, the decay time of the time-resolved PL is prolonged. This is because of delayed carrier transport caused by Γ–X transfer. From these results, it was found that marginal type-I SLs present various interesting phenomena that originate from the competitive carrier transport among the Γ miniband, the localized Γ Stark–ladder states, and the X1 state.

We measured temperature dependence of a spin polarization of field-emitted electrons from a single-crystalline magnetite (Fe 3 O 4 ) whisker with 〈1 1 0〉 orientation. The spin polarization of emitted electrons began to increase above 130 K corresponding to the temperature of Verwey point ( T v ). The increase is considered as reflection of the change of the spin state near the Fermi level due to the Verwey transition. Our experimental results support a localization of t 2g orbital electrons below the Verwey point and a model of charge ordering for magnetite.

The paper describes growth of aluminum on a hydrogen terminated Si (100) surface using dimethyl-ethyl amine alane. The growth rate depends on the substrate temperature with an activation energy of 0.56 eV at the temperature ranging from 150 to 250°C. Selective growth of Al into 1.5-μm diameter via-holes is successfully demonstrated at the substrate temperature of 150°C. In situ FTIR measurements suggest that growth of Al occurs by the chemical reaction between AlH 3 and a hydrogen terminated Si surface.

The photoluminescence (PL) and photocurrent (Pc) were measured for GaAs/AlAs type-I superlattices under an applied electric field to investigate Γ – X electron transfer. The PL due to the indirect recombination between the ground X state ( X 1 ) and the ground heavy-hole state (HH 1 ) is clearly observed. In addition, the dips in photocurrent, and enhancement of both intensity and lifetime of the direct PL between the ground Γ ( Γ 1 ) and HH 1 states are observed at the Γ 1 – X n resonant voltages. These results indicate that Γ – X electron transfer significantly influences the electron transport, even in type-I superlattices.

We determined the density of state distribution near the Fermi level in porous silicon from the analysis of the current-voltage (J-V) and the current-thickness (J-T) characteristics in the space-charge-limited-current (SCLC) regime. The distribution exhibits a minimum density at the Fermi level, which is similar to the U-shape-trap-distribution observed in crystalline Si-SiO 2 interface or in amorphous Si. Theoretical analysis well explains both the J V and the J-T characteristics, which implies that the current flow is entirely controlled by localized states situated at the quasi-Fermi level.

We observed two peaks (fast and slow components) in time-resolved photocurrents for type-I GaAs/AlAs superlattices (SLs). The calculations of the envelop function for the SLs showed that the X 1 state in the AlAs barriers resonates with the Γ 2 state in the adjacent GaAs wells at the bias voltage where the slow components become larger. The photoluminescence measurements revealed that some electrons transfer from the Γ 1 to X 1 states and flow through the X 1 – Γ 2 –X 1 – Γ 2 channel at the near X 1 – Γ 2 resonance voltage. The slow component in the transient photocurrents originates from the X 1 – Γ 2 –X 1 – Γ 2 electron transport.

We report on the effects of field-induced Γ–X resonances on carrier transport and optical properties of GaAs/AlAs type-I short-period superlattices (SLs). We have observed an anomalously delayed photocurrent and Γ2-hh1 photoluminescence originating from X1–Γ2 mixing. These observations clearly suggest that electrical conductivity and optical properties even in type-I SLs are seriously affected by X states in the applied electric field.

Light emitting properties of porous silicon annealed under mixed H2 and Ar gas flowing at various temperatures has been examined. Photoluminescence of the porous silicon annealed at 950°C gives a peak at 470 nm with the full-width-at-half-maximum of 50 nm.

Subband-resonance oscillations have been observed in photoexcited, undoped type-II GaAsAlAs superlattices. The frequency can be tuned over a wide range either by the applied voltage or the photoexcited carrier density. The oscillations can be explained by an oscillating space-charge which forms the domain boundary between two electric-field regions, which are attributed to negative differential velocity originating from X-related resonant tunneling.

This paper deals with the structural characterization and the optical properties of deuterium terminated porous silicon (D-PS) fabricated by electrochemical anodization with DF-ethanol-D6 isotope electrolyte. Both the deuterium terminated and the usual hydrogen terminated porous silicons (H-PS) were characterized with transmission electron microscope analysis and Fourier transform infrared spectroscopy. These characterizations show that the nanometer crystalline structure of D-PS is almost the same as that of H-PS except for the surface termination. Although both PS show the same valence band energy shift, which was confirmed by X-ray photoemission spectroscopy, the photoluminescence spectrum of D-PS was different from that of H-PS. These results indicate that the surface vibration of terminated atoms couples to the excited energy states of quantum-confined carriers, which induces the surface-trapped states of Si nanocrystals.

In this paper, the electron emission from a cathode with a large number of emission sites is discussed by introducing a distribution function of the field enhancement factor β. After accounting for the distribution of the field enhancement factor, the field electron emission from the cathode deviates from the classical Fowler–Nordheim (F–N) theory, the F–N plot is not a straight line and bends up in region of low electric field. A good agreement of the calculated results with experimental results was achieved by employing a reasonable distribution function of β.

(Y 1− x La x ) 2 O 3 :Eu,Zn phosphors have been prepared by a citric acid gel method to develop a red-emitting phosphor with high luminance and good chromaticity under a low excitation voltage. The dependence of structural and luminescent properties on the composition ratio of La/Y and on the Zn addition was investigated. The La addition of x = 0.1 improves structural, cathode luminescence (CL) luminance, CL efficiency and chromaticity for the (Y 1− x La x ) 2 O 3 :Eu phosphors. Though the Zn doping has a tendency of further improvement in structure, CL luminance, CL efficiency and chromaticity, the Y 2 O 3 :Eu,Zn phosphor without La addition shows the best characteristic.

Non-linear behaviors of both photoluminescence (PL) spectra and picosecond PL decay were studied as a function of the excitation intensity of femtosecond laser pulses in porous silicon. With increasing excitation intensity, blue-green PL appears, whereas the red PL intensity shows saturation. Picosecond decay measurements reveal the existence of both a faster decay component of the order of 100 ps and a slower one of the order of microseconds, at room temperature. These results can be quantitatively explained by a three-level model. The origin of the blue luminescence under high excitation is also discussed.

Electron paramagnetic resonance spectroscopy has been applied to investigate the properties of porous silicon formed on a (100)-oriented p-type silicon wafer prepared by anodisation. When anodisation was carried out in an electrolyte solution of HF(·H2O), H2O and C2H5OH with a volume ratio of 1 : 0 : 1, two different types of resonance were observed: one of which was of angular dependence which was coincident with the Pbl centre formed on the Si(100) surface, and the other was independent of the angle between the 〈0 1 1〉 axis of the silicon wafer and the applied magnetic field. For the porous silicon prepared in an electrolyte solution of HF(·H2O), H2O and C2H5OH with a volume ratio of 1 : 1 : 2 an angular-independent anisotropic signal with g⊥ = 2.0014 and g⊥ = 2.0064 was observed. This seemingly looks a signal with g = 2.005, but the difference g⊥ − g⊥ is larger than that for the dangling bonds in amorphous Si. It is therefore presumed that the resonances observed in this study are assigned to Pbl at the surface of Si(100) and Pb-like centres in nano-size crystallites.

We will describe here the fabrication and emission characteristics of two new types of wedge-shaped silicon emitters. These emitters are easily fabricated using anisotropic etching of silicon without high-resolution lithography. For both emitters we obtained the emission currents which follow the Fowler-Nordheim relation.

We have studied ultrafast relaxation processes in porous silicon using a femtosecond pump and probe pulse-correlation technique at 440-nm wavelength. We have observed photoinduced absorption with a response time of the order of 5 ps. In addition to this fast relaxation process, we have also observed a strong induced absorption change on millisecond timescales. From the observation of the picosecond response, the relevant carrier dynamics is clarified as follows: carriers are excited in Si microcrystals and then rapidly thermalize to the surface states within 5 ps. The observation of the strong absorption change on millisecond timescales suggests the possibility of fabricating optical logic gates or all-optical modulators using porous silicon.

We have fabricated a light-emitting diode based on a pn junction of microcrystalline silicon carbide (μc-SiC) and porous silicon (PS). The μc-SiC/PS junctions showed rectification behaviour, and a uniform red electroluminescence (EL) in the forward direction. The EL mechanism is interpreted as the recombination of electron-hole pairs doubly injected into the PS layer. No degradation was observed in the EL intensity during measurements over 8 hours. These results mean that n-type μc-SiC serves well as an electron injector to PS.

We have prepared a p-type microcrystalline silicon carbon thin film by an electron cyclotron resonance plasma-enhanced chemical vapor deposition using a Si(CH 3 ) 4 + SiH 4 + B 2 H 6 + H 2 gas mixture. The p-type μc-SiC had an optical band gap of around 2.4 eV, a dark conductivity of around 10 −2 S/cm and a C/Si ratio of around 0.02, which had almost similar values as the p-type μc-SiC prepared with a CH 4 + SiH 4 + B 2 H 6 + H 2 gas mixture.

We have investigated the preparation conditions of n-type μc-SiC films with high dark-conductivity (10 -3 -1 S/cm) and wide optical band gap (2.1–2.4 eV) deposited by electron cyclotron resonance (ECR) plasma chemical vapor deposition (CVD) from two kinds of gas sources, SiH 4 + CH 4 + H 2 + PH 3 and SiH 4 + C 2 H 2 + H 2 + PH 3 . It was found that the deposition of the CH 4 -based μc-SiC films required a higher gas pressure (above 2.6 m Torr) than that used for conventional ECR CVD to suppress hydrogen ions impinging on an underlying layer. For the C 2 H 2 -based μc-SiC films, we found that besides the suppression of the hydrogen ions a large supply of the atomic hydrogen and the reduction of the C 2 H 2 /SiH 4 were necessary. We have applied n-type μc-SiC to an electron injector of two kinds of Si-based light emitting diodes whose structures were Al/n-type μc-SiC/i-type a-SiC/a-SiN/p-type a-SiC/SnO 2 /glass, and indium tin oxide/n-type μc-SiC/porous Si/p-type c-Si/Au. In both diodes, we clearly observed visible light emission.

We report a low-power-loss and high voltage X-ray tubes with a graphite nanospines (GNS) cold cathode. The cathode is encapsulated in a glass tube having a Beryllium window with a Tantalum film to generate X-rays. The internal tube pressure was below 10 −7 Pa and a tube current exceeding 1 mA at a tube voltage of 22.9 kV was observed in the fabricated X-ray tube. The tube current dispersion, defined as standard deviation/mean ( σ /mean), was relatively small at 2.4%. An X-ray radiation dose rate exceeding 5 Sv/h was obtained from the X-ray tube and the radiation dose rate dispersion was also small ( σ /mean=0.3%). As an application of the X-ray tube, we demonstrated radiography for the rapid inspection of organic products.

We measured the current-voltage characteristics of n-type c-Si/p-type a-Si:H heterojunctions, and discussed their current transport mechanism. The forward current was characterized by two parts: The current increased with the voltage exponentially (region 1), and non-exponentially (region 2). In region 1, it was found that the current was dominated by a tunneling mechanism, and it was attributed to the recombination of electrons tunneling from c-Si to gap states in a-Si:H and holes captured by the gap states in a-Si:H. In region 2, the current was found to be space-charge-limited (SCLC) due to both electrons injected from c-Si and holes injected from the ohmic contact of p-type a-Si:H. The current transport mechanism of reverse currents depended on the doping level of p-type a-Si:H. The current was considered to be the generation current in a-Si:H for the undoped sample, that in both a-Si:H and c-Si for a boron-doped sample ofB 2 H 6 /SiH 4 = 1 × 10 –5 , and that in c-Si only for a boron-doped sample ofB 2 H 6 /SiH 4 = 1 × 10 –4 . An n-type c-Si/p-type a-Si:H heterojunction was applied to a vidicon-type imaging device, which showed excellent results such as a dark current of 10 nA, a photocurrent of 430 nA/lx and a horizontal resolution of more than 800 television lines.

A two-dimensional contact-type image sensor consisting of hydrogenated amorphous silicon (a Si:H) pin diodes forming an 128 × 128 array with high speed (8 frames/s) and high resolution (16 elements/mm 2 ) has been developed. To obtain a high signal-to-noise ratio and an excellent reproduced image, fabrication of pin diodes with 11 orders of magnitude rectification at ± 4 V and a reverse leakage current below 10 −11 A/mm 2 up to - 15 V required partial elimination of the reactive ion etching (RIE) damage. The resulting sensor showed a signal-to-noise ratio larger than 15 dB at an exposure level of 0.5 lx · s and it could reproduce an image of 200 μm wide stripe lines clearly.

We have prepared μc-SiC:H films with high dark conductivities (10 −3 -1 S/cm) and wide optical band gaps (2.1–2.4 eV) at a higher gas pressure (around 5mTorr) than that for conventional electron cyclotron resonance (ECR) plasma chemical vapor deposition (CVD), with suppression of hydrogen ions impinging on an underlying layer. We have also applied them to a-SiC:H based thin film (TF) light-emitting diodes (LEDs) as electron injectors and obtained the emission over the whole range of visible spectrum from 400 to 780 nm. For a-SiC TF-LEDs, it is the first time that the emission in shorter wavelengths (400–500 nm) has been observed, and it is considered that the improvement of the interface due to the reduction of the process-induced damage during the deposition of μc-SiC:H causes an effective injection of electrons.

We have studied the photoluminescence (PL) mechanism of porous silicon (PS) with various nanocrystal sizes. In as-prepared PS without air exposure, the PL peak energy increases with a decrease of the crystalline size. After air exposure, the PL spectrum is observed in the red spectral region and is independent of the crystal size. The size-dependent PL of as-prepared PS originates from mostly delocalized states, while the red PL of partially oxidized PS originates from localized surface states in Si nanocrystals.