Formation Of Inversion Layer Research Articles

火山ガスと防災

A large amount of SO2 gas was discharged from Miyakejima volcano since the end of September, 2000. The averaged SO2 flux was about 50,000 ton/day in 2000. About 4,000 people could not returned to the island, because SO2 gas has been discharged, and more than 5 ppm of SO2 gas concentrations has been observed frequently around the island. In generally, volcanic gas contains mainly water vapor. The dry gas is largely composed of HF, HCl, SO2 , H2S and CO2 with small amount of N2, H2, He, Ar, CH4 and CO. HF, HCl, SO2 and H2S gases have high toxicity. The volcanic gas disaster occupied about 2.5% of volcanic disaster based on the dead since 1900. In Japan, disasters by volcanic gas occurred 28 times around eleven active volcanoes and 49 people were died during the recent 50 years. Occurrence of volcanic gas disaster is mainly dominated by the configuration of ground around fumarolic area and meterological conditions such as windless, cloudy, foggy weather and formation of inversion layer. SO2 has been released at Oyama volcano in Miyakejima island for more than two years, and the inhabitants had to leave the island. Volcanic gas disaster is influenced by meteorological conditions and local geology. In case of big eruption, volcanic gas ascends to the stratospheric, and aerosol causes low temperature in the world. To reduce the disaster of volcanic gas, it is needed to monitor with a selective gas sensor and to alarm people the forecasted dangers.

Use of near-surface channel conductance and differential capacitance versus potential measurements to correlate inversion layer formation with low effective surface recombination velocities at n-Si/liquid contacts

Near-surface channel conductance measurements, differential capacitance versus potential measurements, and surface recombination velocity measurements have been performed on (111)- and (100)-oriented n-type Si samples in contact with nitrogen and/or liquid electrolyte solutions containing I2, I2/I−, ferrocene+/0, or decamethylferrocene+/0 in either methanol or tetrahydrofuran. Si/liquid contacts that displayed a low effective surface recombination velocity S corresponded to those that formed an inversion layer at the solid/liquid contact as indicated by channel conductance measurements or by differential capacitance versus potential measurements. Contacts that did not produce an inversion layer at the Si surface did not produce low effective S values. The observed behavior is consistent with the known energetics of Si/liquid contacts and provides an explanation for the low effective S values observed in these systems.

Measuring nitrous oxide emission rate from grazed pasture using Fourier-transform infrared spectroscopy in the nocturnal boundary layer

A micrometeorological method is proposed for measuring the nitrous oxide (N 2O) emission rate from grazed pasture. The method was employed at night and used open-path Fourier-transform infrared spectroscopy (FTIR) to simultaneously monitor concentrations of N 2O and carbon dioxide (CO 2) at a height of 3 m in the stable boundary layer. A concentration measurement precision of 1% for 3 min averages was achieved over a 97 m long, open-air absorption path. During calm and clear nights, the formation of a shallow near-surface inversion layer effectively trapped surface gas emissions and led to a build-up of N 2O and CO 2 concentrations near ground level. The ratio of these concentrations was combined with the more readily measured CO 2 emission rate to calculate an area-integrated N 2O emission rate. The method was tested at Hollymount Farm, Springston, New Zealand (43.4°S, 172.3°E, 11 m above sea level) on an early autumn evening. For the Lismore silt loam soil with ryegrass ( Lolium perenne L.) pasture grazed by 10 sheep ha −1 (70 kg impregnated ewes), the stable boundary layer concentration increases of N 2O and CO 2 were highly correlated (0.080±0.008 ppb/ppm, r 2=0.83, n=201, 3 min averages). The CO 2 and N 2O emission rates averaged 130±38 μg C m −2 s −1 and 24±5 ng N m −2 s −1, respectively, for a soil temperature of 19 °C. For synthetic-urine patches and untreated (but previously grazed) areas, soil cover/chamber measurements yielded N 2O emission data of 5–24 and 0–6 ng N m −2 s −1, respectively. This illustrated the value of chambers for determining spatial variability, suggested most of the N 2O emissions were from urine patches, and emphasised the challenge of integrating small-scale emission measurements.

Role of inversion layer formation in producing low effective surface recombination velocities at Si/liquid contacts

Photoconductivity decay lifetimes have been obtained for NH4F(aq)-etched Si(111) and for air-oxidized Si(111) surfaces in contact with solutions of CH3OH or tetrahydrofuran (THF) containing either ferrocene+/0 (Fc+/0), bis(pentamethylcyclopentadienyl) Fe+/0, or I2. Si surfaces in contact with electrolytes having Nernstian redox potentials >0 V versus the standard calomel electrode exhibited low effective surface recombination velocities regardless of the different surface chemistries, whereas those exposed only to N2(g) ambients or to electrolytes containing mild oxidants showed differing rf photoconductivity decay behavior depending on their different surface chemistry. The data reveal that formation of an inversion layer, and not a reduced density of electrical trap sites on the surface, is primarily responsible for the long charge-carrier lifetimes observed for Si surfaces in contact with CH3OH or THF electrolytes containing I2 or Fc+/0.

Lidar observations of the middle atmospheric thermal tides and comparison with the High Resolution Doppler Imager and Global‐Scale Wave Model: 1. Methodology and winter observations at Table Mountain (34.4°N)

The tidal signature in the middle atmospheric thermal structure was investigated using more than 140 hours of nighttime lidar measurements at Table Mountain (34.4°N) during January 1997 and February 1998. The lidar profiles (30–85 km) revealed the presence of persistent mesospheric temperature inversions around 65‐ to 70‐km altitude with a clear local solar time (LST) dependence. Daytime temperature profiles (65–105 km) obtained by the High Resolution Doppler Imager (HRDI) on board the Upper Atmosphere Research Satellite (UARS) in January and February from 1994 to 1997 and zonally averaged at the latitude of the Table Mountain Facility (TMF) were considered together with the lidar results. The daytime HRDI and nighttime lidar temperature differences from their respective daytime and nighttime averages were compared to the equivalent differences predicted by the Global Scale Wave Model (GSWM). A remarkable consistency was observed between the lidar and the HRDI upper mesospheric thermal structure, with a continuous downward propagation of warm temperatures from 100 km at 1000 LST to 75 km at 2000 LST and 65–70 km at 0300–0500 LST, surrounded above and below by colder temperatures. This structure was predicted by GSWM but with a 2‐ to 4‐hour delay and a weaker amplitude. On the lower side of this structure (i.e., 65–70 km) a thin layer, characterized by early night cold temperatures and late night warm temperatures, was identified as the result of the downward propagation of the temperature inversions. Using a new analysis technique, which we have named “constrained wave adjustment” for convenience in future reference, and assuming that the observed temperature variability was entirely driven by tides, some estimations of the diurnal and semidiurnal phases and amplitudes were made from the lidar measurements between 40‐ and 85‐km altitude. Although it does not allow a complete and accurate extraction of the tidal components, this new method appeared to work well for the present TMF study. The estimated diurnal amplitude exhibited a minimum at 63 km with a fast phase transition, characteristic of the transition between the upper stratospheric trapped modes (phase at 1800 LST) and the upward propagating modes. This transition layer was predicted by GSWM to be at 5‐km lower altitude. This altitude shift was present throughout the middle mesosphere. Immediately above the transition layer, the very fast growing diurnal amplitude between 65 and 72 km was followed by a substantial decrease and by the emergence of the semidiurnal component, resulting in the formation of the mesospheric temperature inversion layers. However, the amplitude of the inversions remained large compared to the theoretical tidal predictions and a different formation mechanism should possibly be considered. Recent modeling studies have shown that gravity wave breaking can be significantly affected by the tidal background winds and some preferential wave breaking times could emerge that are dependent on the phase of the diurnal tide and the characteristics of the dissipating waves. This “LST filtering” could result in LST‐dependent temperature inversion layers similar to those observed by lidar. The new analysis technique presented in this paper was also applied to study the temperature tidal oscillations at Mauna Loa Observatory (19.5°N). The results are presented in a companion paper [Leblanc et al., this issue].

The Formation and Destruction of Inversion Layers within a Deep Valley

The technique of large-eddy simulations has been used to investigate thermally driven local circulations in deep valleys for a complete diurnal cycle. A soil model simulates the thermal forcing at the ground, which depends on the season, the soil characteristics, the valley orientation, and the atmospheric variables. The scales of interest are characteristic of an urban site located in a mountainous area, and the research focuses on low wind conditions without the influence of large-scale pressure gradients. This study highlights the influence of the season on the mechanisms responsible for the formation and the destruction of the thermal inversion layer. The spatial distribution of the convective boundary layer (CBL) within the valley is directly influenced by the season because of the variation of the solar warming. In summer, the altitude of the top of the CBL remains approximately constant across the valley, whereas in winter, this altitude varies with its location within the valley.

Influence of the diurnal tide and thermospheric heat sources on the formation of mesospheric temperature inversion layers

One hundred eighty nine hours of mesopause region temperature, meridional wind, and Na density measurements were made at the Urbana Atmospheric Observatory (40°N, 88°W) during both day and night in Sep/Oct 1996. The data are used to study tidal oscillations and their relationship to mesospheric temperature inversion layers. The observations show that thermospheric forcing by UV and EUV absorption plays an important role in establishing the tidal characteristics in the upper mesosphere. Because of the large tidal amplitudes and strong thermospheric heating during the day, the general characteristics of the background temperature structure can only be established by measuring temperature throughout the diurnal cycle. When the temperature profile is averaged over the complete diurnal cycle, the mesopause is considerably warmer (196 K compared to 190 K) and lower (96 km compared to 101 km) than that observed at night. Furthermore, there is little evidence of the prominent inversion layers frequently reported in nighttime measurements. These features appear to be artifacts associated with incomplete sampling of the strong diurnal tide.

Evidence For Heterojunction Effects in Polycrystalline Si1-xGex Thin Film Transistors With Si Caps

AbstractPolycrystalline silicon-germanium (poly-Si1-xGex) thin film transistors (TFTs) werefabricated with and without Si interlayers (caps) to buffer the SiO2 gate dielectric and theSi1-xGex channel. Both low temperature processes (≤ 550 °C) compatible with glass for flat panel displays and high temperature processes were used. NMOS TFTs show dramatic performanceimprovements up to moderate (5 to 10 nm) interlayer thicknesses. In contrast, PMOS TFTs showonly small improvements at low interlayer thicknesses (< 5 nm), after which performancedeclines. Computer simulations using an effective medium model for polycrystalline materialssuggest that in addition to interface improvement, a pseudomorphic heterojunction is formedfrom the strained Si cap and unstrained poly-Si1-xGex channel with both conduction and valenceband offsets. These offsets play a significant role in inversion layer formation.

Numerical analysis of field-effect surface passivation for solar cells

In order to investigate the influence of surface potential on the electric characteristics of solar cells, the characteristics of conventional cells and back-contact type high-efficiency silicon cells were analyzed using 2-dimensional numerical simulation, varying the surface electrical potential. The locations where surface electrical potential is controlled are the rear side in conventional cells and the front side in back-contact cells. As a result of the calculations, it was found that field-effect surface passivation yields cell characteristics equivalent to those of a cell with effective surface recombination velocity of 0 cm/s, even if the cell has a poor Si SiO 2 interface (i.e., D it > 1.0 × 10 11cm −2eV −1). It was also found that both the use of a higher resistivity wafer and — especially in p-type substrates — the formation of inversion layers causes the field-effect surface passivation to work the fullest effect. In addition, a computer simulation based on physical-parameter measurements taken from actual materials forecasts that a back-contact cell would realistically be able to exceed 25% efficiency under AM1.5 global, one-sun illumination.

Quasistatic and high frequency capacitance–voltage characterization of Ga2O3–GaAs structures fabricated by in situ molecular beam epitaxy

Interface properties of Ga2O3–GaAs structures fabricated using in situ multiple-chamber molecular beam epitaxy have been investigated. The oxide films were deposited on clean, atomically ordered (100) GaAs surfaces at ≂600 °C by electron-beam evaporation using a Gd3Ga5O12 single-crystal source. Metal–insulator–semiconductor structures have been fabricated in order to characterize the Ga2O3–GaAs interface by capacitance–voltage measurements in quasistatic mode and at frequencies between 100 Hz and 1 MHz. The formation of inversion layers in both n and p-type GaAs has been clearly established. Using the quasistatic/high frequency technique, the interface state density has been derived as a function of band gap energy and a midgap interface state density in the mid 1010 cm−2 eV−1 range has been inferred. Charge trapping in the oxide has been revealed as the dominant trapping mechanism.

Low Interface State Density Oxide-GaAs Structures Fabricated by In-Situ Molecular Beam Epitaxy

AbstractWe have extended the spectrum of molecular-beam epitaxy (MBE) related techniques by introducing in-situ deposition of oxides. The oxide films have been deposited on clean, atomically ordered (100) GaAs wafer surfaces using molecular beams of gallium-, magnesium-, silicon-, or aluminum oxide. Among the fabricated oxide-GaAs heterostructures, Ga2O3-GaAs interfaces exhibit unique electronic properties including an interface state density Dit in the low 1010 cm−2eV−1 range and an interface recombination velocity S of 4000 cm/s. The formation of inversion layers in both n- and p-type GaAs has been clearly established. Further, thermodynamic and photochemical stability of excellent electronic interface properties of Ga2O3-GaAs structures has been demonstrated.

The mechanism of formation of inversion layers in the mesosphere

Mesospheric temperature profiles obtained by Rayleigh lidar in the south of France frequently show winter temperature inversions, with an amplitude up to 40K in a few km. A 2D dynamic model, developed to interpret these observations, showed that the mesospheric inversions were mainly due to the vertical circulation induced by the breaking of gravity waves in the upper mesosphere.

New phenomena observed in electrochemical micromachining of silicon

This paper reports on electrochemical micromachining experiments, including a new passivation technique and several phenomena observed in I-V characteristics of Si in KOH, which have not been published in the literature so far. An energy-band diagram representation of the solid-state physics is utilized as a qualitative tool to understand some of these effects. A series of experiments has been carried out to find the optimum bias voltages for etching the p substrate and for passivation of the n regions, including lightly doped deep n diffusions and heavily doped shallow n + regions. A new passivation effect has been observed during these experiments. This new effect is that in the presence of an exposed p-n junction at the Si/KOH interface, the p-type material does not etch when both sides of the junction are held at the open-circuit potential (OCP), although one would normally expect that both sides of the p-n junction would be etched away. With the aid of the energy-band diagram representation, this fact is explained in terms of n-type inversion layer formation at the surface. Other phenomena observed in the I-V characteristics are associated with the illumination. The first concerns (100) n-type material, which exhibits a negative shift in the I-V characteristics for bias voltages around the passivation potential, PP. This is due to the photoinduced holes, which accelerate the oxide growth, thereby reducing the PP. In p-type Si, illumination causes an anodic shift in the I-V characteristic for positive currents. This is due to the photoinduced electrons, which decrease the band bending by filling the available states of the deeply depleted p-type surface. At voltages less than the OCP, the I-V characteristic shows a current runaway when the sample is illuminated.

Evaluation of electrical properties of vanadium suicide-silicon Schottky diodes formed by ion implantation

Vanadium suicide Schottky diodes are fabricated using high-dose ion implantation on p-type single-crystal silicon substrates. Their electrical properties are evaluated using the resistivity, current-voltage ( I V), and capacitance-voltage ( C V) techniques. The resistivity of these layers decreases on annealing, and a metallic behaviour of the suicide surface layer is observed. The temperature coefficient of resistance (a) is found to be 6.8 × 10 −3/K. The barrier height φ b measured using the I V technique is 0.75 eV. This high value of φ b is the result of formation of inversion layer at the suicide-silicon interface. On annealing the diode at 750°C for 30 min, the ideality factor n improves to 1.01 indicating that the current transport is mainly by the thermionic emission process across the junction. The φ b value measured using the Cz. sbnd; V method differs from that obtained by I V measurements. This discrepancy is attributed to the presence of multiphase suicide contact and the implant damage.

Electro-optical properties of polymeric semiconductor devices constructed from poly (3-hexyl thienylene)

MIS structures fabricated with a conjugated polymer as the active semiconductor are well suited for the investigation of charge storage in self-localised excitations. In such a structure, the gate electrode is used to control the surface or space charge densities; the formation of accumulation and inversion layers being of particular interest as charge is introduced into the polymer without associated dopant ions. We report measurements of the electrical and optical properties of devices fabricated with poly (3-hexyl thienylene).

Formation of surface inversion layer in F +-implanted n-type silicon

Influences of fluorine ion implantation on the electrical properties of n-type silicon have been investigated by electron beam induced current (EBIC), Hall and metal-oxide-semiconductor (MOS) high frequency capacitance-voltage (HFCV) measurements. A grating mask was used to delineate the implantation region so that the F +-implanted and unirradiated areas were located in the same A1/n-type Si Schottky diode region. EBIC images, obtained with different electron beam energies, normal and parallel to the diode surface, and EBIC collection efficiencies in the implanted and unirradiated areas were recorded. Fitting data of energy dependent EBIC collection efficiency into the theoretical EBIC model of Schottky diode, the thickness of the metal layer, depletion layer width, minority carrier diffusion length in the substrate and EBIC collection efficiency in the deletion region were determined. The minority carrier recombination in the fluorine implanted area was found to be higher than that of the blank Si area under Schottky contact. Outside the Schottky contact, an inversion layer was observed to form at the surface of the implanted area. The structural perfection of the F + implanted area was investigated by cross-sectional transmission electron microscopy (XTEM). The p-type characterization in the surface layer of the F + implanted area was also confirmed by the Hall and HFCV measurements.

Heterostructure complementary technology

A complementary inverter configuration based on two new heterostructure field-effect devices is proposed. The FETs are fabricated in a common substrate grown by molecular-beam epitaxy. The devices rely on the formation of inversion layers at heterojunction interfaces.

Electrical and electrochemical properties of pretreated thermally and γ-irradiated TiO2

Electrical conductivity and Seebeck voltage developed in thermally pretreated and γ-irradiated TiO2 was measured as a function of temperature. The conversion of n-type TiO2 into p-type and vice versa observed after irradiation was explained in terms of ionization of Ti3+ donors and lattice O= species, subsequent trapping of carriers in adsorbed oxygen and further formation of p-type inversion layer on the oxide surface during irradiation. The sign of the EMF of the electrochemical Ag/Ag+ concentration cell by the addition of heated and γ-irradiated TiO2 in one of the compartment of the cell was found to be opposite to that due to the addition of the corresponding heated but non-irradiated oxide sample.

Electrical conductivity and electrochemical properties of γ-irradiated TiO2

Electrical conductivity and Seebeck voltage developed in γ-irradiated TiO2 was studied as a function of temperature. The conversion of n-type TiO2 into p-type observed after irradiation was explained on the basis of formation of inversion layer of p-type TiO2 due to the chemisorption of oxygen on the oxide surface during irradiation. Sign of the EMF of the electrochemical concentration cell of Ag/Ag+ with the addition of irradiated TiO2 was found to be exactly opposite to that due to the addition of nonirradiated oxide.

The interaction of oxygen with InSb(110) surfaces

The room-temperature adsorption of molecular, unexcited oxygen on InSb(110) surfaces either cleaned by sputtering-annealing techniques or cleaved by the wedge technique has been investigated as a function of the surface disorder. Auger electron spectroscopy, reflection high energy electron diffraction, low energy electron diffraction, and field effect spectroscopy are employed to analyse from the correlations of chemical, structural, and electronic properties the initial stages of oxygen sorption. A two-stage adsorption process has been found on either disordered or ordered surfaces. In the initial stage of adsorption the coverage increases with exposure depending on the surface disorder, and oxygen is suggested to adsorb at defect sites. The main chemisorption shows a saturation in coverage at high exposures with the oxygen presumably adsorbed at regular lattice sites. The oxygen adsorption causes changes of band bending indicating for the p-substrates the formation of inversion layers.