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The field determinations of crustal electrical conductivity/depth profiles show anomalously high conductivities in the lower crust. This has yet to be explained by a consistent theory and interpretation of field results is difficult due to the lack of laboratory conductivity measurements of saturated rocks at lower crustal temperatures. A cell was designed to measure the electrical conductivity of saturated rocks up to the lower crustal conditions of; confining pressures of 1 GPa, pore-fluid pressures of 1 GPa and temperatures of 900°C. This complex exercise required the use of a metal sleeve and the use of guard-ring techniques to remove leakage currents induced by the sleeve. The development of the cell involved several years work and is a breakthrough in measurement techniques as it has enabled the measurement of saturated rock conductivities at lower crustal temperatures and high pressures for the first time. The conductivity of 14 samples of acidic and metabasic rocks was measured at a variety of confining pressures (<0.2 GPa), porefluid pressures (<0.2 GPa), temperatures (<900°C) and saturation fluids. The pressure variations showed that the basic rocks had a conductivity too high to be explained by conduction through saturating electrolyte alone. The temperature variation showed a dramatic difference between acidic and basic rocks. The acidic rocks showed large decreases in conductivity above 350°C after initial rapid increases in conductivity. The basic rocks showed no such reduction in conductivity indicating that a conduction mechanism in addition to pore-fluid conduction was present. Results indicate that saturated -rocks at high temperatures have 7/ conductivities sufficient to explain the high conductivity layers in the upper lower crust whereas acidic rocks do not. The results also demonstrate that graphite may be an important additional conduction mechanism possibly accounting for the moderately high conductivities in the lower lower crust even in the absence of electrolyte conduction

In this study reliable film type NTCR thermistors based on NiMn(_2)O(_4)+δ were produced and their electrical properties were studied in detail. Electron-beam evaporation procedures have been applied to produce thin film NTCR thermistors. Phase pure NiMn(_2)O(_4)+δ target material was produced via a traditional ceramic precursor oxide route and thin films were deposited in an optimised procedure. The thickness distribution of evaporated films showed good agreement with a theoretical model, derived from evaporation theory and the sticking coefficient of the vapour on the substrates was approximately 80% ± 1.5%. The composition of electron-beam evaporated films was found to be not controllable in terms of the phase purity and the Ni : Mn ratio. In order to avoid these problems thick film NiMn(_2)O(_4)+δ NTCR thermistors were developed using direct screen-printing techniques. Detailed Rietveld refinement analysis was carried out for the source powder used for screen-printing. The main focus of the work was the measurement of resistance-temperature (R-T) characteristics of thin and thick films and pellets. In the temperature range of concern (77 K -550 K) conduction was found to be by variable-range hopping (VRH) and nearest-neighbour hopping (NNH); R ~ exp (TʆT)(^p), where the index p depends on the mode of hopping. Detailed analysis of R-T data showed that screen-printed films and pellets exhibited a p-value of 0.5, which was identified with VRH with a parabolic density of states (DOS) with an exponential dependence of resistance: R ~ exp (TʆT)(^0.5). For electron-beam evaporated films the mechanisms detected were NNH: R ~ exp (TʆT); and VRH with a constant DOS {p = 0.25) following: R ~ exp (TʆT)(_0.25). For screen-printed films with incorporated glass phase the electrical conduction mechanism was analysed using a.c. impedance spectroscopy and at low frequencies the hopping conduction was in agreement with the d.c. behaviour. The time constant of this mechanism could be described by an equivalent circuit containing a RC element. For higher frequencies a second mechanism was found, best described by a CRL element.

The influence of pre-metallisation surface preparation on the structural, chemical, and electrical properties of metal-nGaN interfaces has been investigated by X-ray Photoemission Spectroscopy (XPS), current-voltage measurement (I-V) and cross section Transmission Electron Microscopy (TEM). XPS analysis showed that the three GaN substrate treatments investigated, ex-situ HF etch, in-situ anneal in Ultra-High-Vacuum (UHV), and in-situ Ga reflux cleaning in UHV result in surfaces increasingly free of contaminants. Additionally, the three treatments are found to induce increasingly larger upward band bending. Ag-nGaN contacts formed after Ga reflux cleaning exhibit a Schottky barrier height of 0.80 eV and an ideality factor of 1.56, as determined by I-V.XPS and TEM characterisation of Au-nGaN formed after the three pre-metallisation surface treatments show that HF etching and UHV annealing produce abrupt, well-defined interfaces. Conversely, GaN substrate cleaning in a Ga flux results in Au/GaN intermixing. I-V characterisation of Au-nGaN contacts yield a Schottky barrier height of 1.25 eV with very low ideality factor and very good contact uniformity for the pre-metallisation UHV anneal while the Ga reflux cleaning result in a much lower barrier (0.85 eV), with poor ideality and uniformity. I-V and XPS results suggest a high density of acceptor states at the surface, which is further enhanced by UHV annealing. The mechanisms of Ga-nGaN, Ag-nGaN and Au-nGaN Schottky barrier formation are discussed in the context of the Metal-Induced Gap States model (MIGS) Unified Defect Model (UDM) and Cowley-Sze model.

AlN thin films grown on GaN/Sapphire substrate by RF magnetron sputtering technique with AlN target has been studied. Simple MIS capacitor was fabricated in order to evaluate the electrical properties of AlN films that played as a insulator. Various microstructures of AlN thin films can be obtained by controlling the growth parameters, such as sputtering powers, sputtering distances and working pressure. The microstructures of the AlN films were examined by X-ray diffraction. The observation of the surface morphology ,the distribution of defects and the interface of AlN/GaN were performed by transmission electron microscopy. The results showed that the amorphous AlN thin films were obtained with a 21cm long sputtering working distance and under the 100W sputtering power and 8mtorr working pressure conditions. The results of the C-V measurement indicated that the MIS device demonstrated a capacitor behavior, however a large leak current showed up in the end. The quality of the AlN films and the process procedures of MIS device still need be improved further.

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国立情報学研究所で電子化したコンテンツを使用している。

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The Hall coefficient and conductivity of silicon films vacuum deposited on 0° and 60° sapphire at 850°C to 1050°C were measured from 100°K to 550°K. Films made from 0.094 Ω-cm p type and 1 Ω-cm n type silicon sources were prepared by electron bombardment heating of the source in a vacuum of 5 x 10⁻⁷ to 10⁻⁶ torr. The orientation and crystallinity of the films were investigated using electron diffraction. It was found that defects in the films introduced both donor and acceptor levels. The heavy compensation thus produced in films deposited at lower temperatures lead to a very low hole concentration. All films were p type at room temperature showing that the acceptor levels slightly dominated the donor levels. The films deposited on 0° sapphire indicated fewer defects than those deposited on 60° sapphire. At high temperature (> 950°C) doping of the silicon by aluminum atoms from the substrate was appreciable. The Hall mobility of the films made from the p type source material decreased with increasing temperature of deposition. This apparent anomaly is explained by the use of the polycrystalline film model suggested by Volger (1950). / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate