Langmuir-Blodgett (LB) films have previously been used as organic insulating layers in compound semiconductor metal-insulator- semiconductor devices, with promising preliminary results. This thesis describes the first investigation of the use of LB films In gallium arsenide metal-insulator-semiconductor devices. Diodes incorporating thin layers of w-tricosenoic acid or substituted copper phthalocyanine possessed 'leaky' electrical characteristics, i.e. there is some conduction through the LB film. This 'leaky' behaviour was exploited to produce the first metal- Insulator-semiconductor-switch (MISS) incorporating an LB film. MISS devices on n-p(^+) GaAs were produced with good switching characteristics and a high yield (~90%), using LB film thicknesses between 9 and 33 nm. It was shown that the 'punch through' mechanism was responsible for the switching behaviour. p-n(^+) GaAs/LB film MISS diodes behaved rather differently, with good switching characteristics only found at reduced temperature. Some degradation of the characteristics of LB film MISS devices was noted, although this was reduced by using the more robust phthalocyanlne LB films. Metal-tunnel-insulator-semiconductor diodes were produced on the ternary alloy Ga(_.47)In(_.53)As, using LB film monolayers. The barrier height was apparently larger than that of Schottky barriers on this material, with a very substantial reduction in current density due to tunnelling through the LB film. Using this technique it may be possible to produce very high performance GaInAs fleld-effect-transistors, which are analogous to GaAs metal-semiconductor field effect transistors.

This thesis studies the effects of gas ambients on the electrical properties of the insulator-semiconductor interface of a MIS capacitor. A microcomputer-controlled instrumentation system has been developed to extract this information from measurement of the a.c. admittance of MOS or MIS devices. The system incorporates several novel developments in circuitry and software which enable these admittance data to be automatically collected and processed in the frequency domain by remote recalibration of the instrumentation. This advancement permits interface state density information to be calculated more quickly and accurately than has been previously possible using manually-operated equipment. The system has been used to investigate the influence of gases on the density of interface states in a MIS capacitor, in particular the palladium/silicon dioxide/silicon structure which is sensitive to hydrogen gas. A distinct change in the distribution of surface state density across the silicon bandgap has been observed upon exposure to a hydrogen ambient. An alternative insulating layer, an organic Langmuir-Blodgett film multilayer of ω-tricosenoic acid, has been characterised and examined, and increased sensitivity of this structure to hydrogen gas has been indicated.

Metal-insulator-semiconductor switches (MISS), in which the T denotes some form of thin semi-insulating layer and the semiconductor part consists of a pn junction, are part of the general class of regenerative switching devices which includes the thyristor. The switching behaviour of the MISS derives from the ability of the MIS junction to exhibit current gain and to exist in two modes, deep depletion and inversion. In this thesis, a general model for the regenerative switching is proposed after investigating the properties of the MIS junction both theoretically and experimentally. Results from MIS diodes with tunnelling-thickness oxide Mayers indicate that interface states play a dominant role in their electrical behaviour and that the uniformity of the oxide is poor, giving rise to a large spread in the current-voltage characteristics. Subsequently, the epitaxial form of the MISS device is investigated and in particular the importance of isolation of the pn junction. It is concluded that spreading effects set a practical lower limit to the device dimensions, making the epitaxial form unsuitable for microelectronic applications. An alternative semi-insulator, 'silicon-rich oxide' (SRO) is introduced as an optional I-layer with possibly greater integrity than tunnel oxide. MIS diodes formed with SRO are shown to have very similar properties to tunnelling diodes. Large area devices fabricated using this material are surprisingly discovered to exhibit stable negative differential resistance (NDR). Although this discovery at first appears to be contrary to normal circuit stability criteria and to the regenerative feedback model itself, both of these points are resolved. It is shown that the frequency of oscillation of an unstable device is controlled by the external circuit. Then it is proposed that if this frequency is greater than the maximum frequency of operation of the regenerative mechanism, stable NDR is observed. In the final chapter, alternative lateral MISS structures which should overcome the geometrical limitations of epitaxial devices are discussed.

A method of synthesizing and controlling the size of germanium nanocrystals is developed. A tri-layer metal-insulator-semiconductor (MIS) memory device structure comprising of a thin (~5nm) silicon dioxide (SiO₂) layer grown using rapid thermal oxidation (RTO), followed by a layer of Ge+SiO₂ of varying thickness (3 - 6 nm) deposited using a radio frequency (rf) co-sputtering technique, and a capping SiO₂ layer (50nm) deposited using rf sputtering is investigated. It was verified that the size of germanium (Ge) nanocrystals in the vertical z-direction in the trilayer memory device was controlled by varying the thickness of the middle (cosputtered Ge+SiO₂) layer. From analyses using transmission electron microscopy and capacitance-voltage measurements, we deduced that both electrons and holes are most likely stored within the nanocrystals in the middle layer of the trilayer structure rather than at the interfaces of the nanocrystals with the oxide matrix. / Singapore-MIT Alliance (SMA)

The effect of germanium (Ge) concentration and the rapid thermal oxide (RTO) layer thickness on the nanocrystal formation and charge storage/retention capability of a trilayer metal-insulator-semiconductor device was studied. We found that the RTO and the capping oxide layers were not totally effective in confining the Ge nanocrystals in the middle layer when a pure Ge middle layer was used for the formation of nanocrystals. From the transmission electron microscopy and secondary ion mass spectroscopy results, a significant diffusion of Ge atoms through the RTO and into the silicon (Si) substrate was observed when the RTO layer thickness was reduced to 2.5 nm. This resulted in no (or very few) nanocrystals formed in the system. For devices with a Ge+SiO₂ co-sputtered middle layer (i.e., lower Ge concentration), a higher charge storage capability was obtained than with devices with a thinner RTO layer, and the charge retention time was found to be less than in devices with a thicker RTO layer. / Singapore-MIT Alliance (SMA)

We report on the characteristics of a ZnO based metal insulator semiconductor (MIS) diode comprised of a heterostructure of n-ZnO nanorods/n-GaN. The MIS structure consisted of unintentional - doped n type ZnO nanorods grown on n-GaN sample using hydrothermal synthesis at low temperature (100°). The ZnO nanorod layer was vertically grown from the GaN sample, having the diameter 100nm and length 2µm. Then, an insulator layer for electrical isolation was deposited on the top of ZnO nanorod layer by using spin coating method. A metal layer (gold) was finally deposited on the top. The I-V dependences show a rectifying diode like behavior with a leakage current of 2.10⁻⁵ A and a threshold voltage of about 3V. Depend on the thickness of the insulator, the I-V dependences of the n-ZnO/n-GaN heterostructure was varied from rectifying behavior to Ohmic and nearly linear. / Singapore-MIT Alliance (SMA)

<p> This work presents theoretical calculations of some of the most important electrical characteristics of thin film, insulator-dominated semiconductor devices. Solutions of prespecified accuracy for an a.c. transmission line model of the semiconductor in such configurations as the MIS (Metal-Insulator-Semiconductor) structure and the SIS (Semiconductor-Insulator-Semiconductor) structure are given. Together with an accurate solution of the d.c. bias problem, exact C-V (Capacitance-Voltage) and G-V (Conductance-Voltage) characteristics can be found at any frequency. SRH (Shockley-Reed-Hall) impurity centres and surface states have been included in both the d.c. and a.c. solutions. In addition, accurate studies of the low temperature dopant impurity response can be made since the d.c. solution uses full Fermi integrals over arbitrary densities of states with the impurity dopant band treated like an SRH centre for the a.c. solution.</p> <p> In non-equilibrium situations, such as those which occur with the application of light or carrier injection by tunnelling, the a.c. solution requires active elements in the transmission line model but the transmission line can still be solved to a prespecified accuracy provided an accurate solution of the d.c. bias problem can be found. In this thesis the d.c. solution for the case of light-induced pair production is considered under the assumption of bulk controlled d.c. quasi Fermi level shifts. Thus the accuracy of the related a.c. conductance and capacitance solutions is dependent on the reliability of this assumption.</p> <p> The detailed treatment of the a.c. admittance of the MIS structure is justified by its technological importance and fundamental insight gained on impurity centre and surface state effects.</p> <p> The other work presented in this thesis is devoted to a study of a new thin film device structure, the SIS diode. First, the a.c. admittance characteristics for the thick insulator case are predicted to a prespecified accuracy. Then a simple treatment for part of the SIS d.c. tunnelling problem is done to qualitatively predict the effects of such parameters as doping density, temperature and insulator thickness on current-voltage characteristics. Finally, a simple generalization of the a.c. transmission line to include the effects of tunnelling is given which allows accurate solution for the a.c. admittance of tunnelling SIS diodes if the complete d.c. non-equilibrium problem can be accurately solved.</p> <p> Practical application of the thick-insulator SIS diode will undoubtedly stem from its wide range of interesting low and high frequency response characteristics. Among the most interesting of these characteristics is a bell-shaped high frequency C-V response previously unobserved in other two terminal devices.</p> <p> An interesting negative resistance feature, which partly resembles the negative resistance region of the p-n junction tunnel diode, is analyzed for the degenerate SIS p-i-n thin insulator structure. While the thick insulator SIS device has recently been fabricated and the bell-shaped high frequency response experimentally observed, experimental verification of the tunneling characteristics of the SIS diode has as yet not been fully realized.</p> / Thesis / Doctor of Philosophy (PhD)

A metal-insulator-semiconductor (MIS) device with a trilayer insulator structure consisting of sputtered SiO₂ (~50nm)/evaporated pure germanium (Ge) layer (2.4nm)/rapid thermal oxide (~5nm) was fabricated on a p-type Si substrate. The MIS device was rapid thermal annealed at 1000°C. Capacitance-voltage (C-V) measurements showed that, after rapid thermal annealing at 1000°C for 300s in Ar, the trilayer device exhibited charge storage property. The charge storage effect was not observed in a device with a bilayer structure without the Ge middle layer. With increasing rapid thermal annealing time from 0 to 400s, the width of the C-V hysteresis of the trilayer device increased significantly from 1.5V to ~11V, indicating that the charge storage capability was enhanced with increasing annealing time. High-resolution transmission electron microscopy results confirmed that with increasing annealing time, the 2.4nm amorphous middle Ge layer crystallized gradually. More Ge nanocrystals were formed and the crystallinity of the Ge layer improved as the annealing time was increased. When the measurement temperature was increased from –50°C to 150°C, the width of the hysteresis of the MIS device reduced from ~10V to ~6V. This means that the charge storage capability of the trilayer structure decreases with increasing measurement temperature. This is due to the fact that the leakage current in the trilayer structure increases with increasing measurement temperature. / Singapore-MIT Alliance (SMA)

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第22072号 / 工博第4653号 / 新制||工||1725(附属図書館) / 京都大学大学院工学研究科電子工学専攻 / (主査)教授 木本 恒暢, 教授 川上 養一, 准教授 杉山 和彦 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

This dissertation tested the hypothesis that energy transferred from a plasma or plume can be used to optimize the structure, chemistry, topography, optical and electrical properties of pulsed laser deposited and sputtered thin-films of ZnO, a-BOxNy, and few layer 2H-WS2 for transparent electronics devices fabricated without substrate heating or with low substrate heating. Thus, the approach would be compatible with low-temperature, flexible/bendable substrates. Proof of this concept was demonstrated by first optimizing the processing-structure-properties correlations then showing switching from accumulation to inversion in ITO/a-BOxNy/ZnO and ITO/a-BOxNy/2H-WS2 transparent MIS capacitors fabricated using the stated processes. The growth processes involved the optimization of the individual materials followed by growing the multilayer stacks to form MIS structures. ZnO was selected because of its wide bandgap that is transparent over the visible range, WS2 was selected because in few-layer form it is transparent, and a-BOxNy was used as the gate insulator because of its reported atomic smoothness and low dangling bond concentration. The measured semiconductor-insulator interfacial trap properties fall in the range reported in the literature for SiO2/Si MOS structures. X-ray photoelectron spectroscopy (XPS), Hall, photoluminescence, UV-Vis absorption, and X-ray diffraction (XRD) measurements investigated the low-temperature synthesis of ZnO. All films are nanocrystalline with the (002) XRD planes becoming more prominent in films grown with lower RF power or higher pressure. Low power or high chamber pressure during RF magnetron sputtering resulted in a slower growth rate and lower energetic conditions at the substrate. Stoichiometry improved with RF power. The measurements show a decrease in carrier concentration from 6.9×1019 cm-3 to 1.4×1019 cm-3 as power increased from 40 W to 120 W, and an increase in carrier concentration from 2.6×1019 cm-3 to 8.6×1019 cm-3 as the deposition pressure increased from 3 to 9 mTorr. The data indicates that in the range of conditions used, bonding, stoichiometry, and film formation are governed by energy transfer from the plasma to the growing film. XPS characterizations, electrical measurements, and atomic force microscopy (AFM) measurements reveal an increase in oxygen concentration, improved dielectric breakdown, and improved surface topography in a-BOxNy films as deposition pressure increased. The maximum breakdown strength obtained was ~8 MVcm-1, which is comparable to a-BN. Metal-Insulator-Metal (MIM) structures of a-BOxNy grown at 10 and 15 mTorr suggest a combination of field-enhanced Schottky emission and Frenkel-Poole emission are likely transport mechanisms in a-BOxNy. In comparison, better fitted data was gotten for field enhanced Schottky emission which suggests the more dominant mechanism. The static dielectric constant range is 3.26 – 3.58 for 10 and 15 mTorr films. Spectroscopic ellipsometry and UV-Vis spectroscopy measured a bandgap of 3.9 eV for 15 mTorr grown a-BOxNy. 2H-WS2 films were grown on both quartz and a-BOxNy which revealed that the XRD (002) planes became more prominent as substrate temperature increased to 400 oC. AFM shows nano-grains at lower growth pressure. Increasing the growth pressure to 1 Torr resulted in the formation of larger particles. XPS chemical analysis reveals improved sulfur to tungsten ratios as pressure increased. Sulfur deficient films were n-type, whereas sulfur rich conditions produced p-type films. Frequency dependent C-V and G-V measurements revealed an interface trap concentration (Nit) of 7.3×1010 cm-2 and interface state density (Nss) of 7.5×1012 eV-1cm-2 for the transparent ITO/a-BOxNy/ZnO MIS structures, and approximately 2 V was required to switch the a-BOxNy/ZnO interface from accumulation to inversion. Using 2H-WS2 as the channel material, the ITO/a-BOxNy/2H-WS2 required approximately 4 V to switch from inversion to accumulation in both n and p-channel MIS structures. Interface trap concentrations (Nit) of 1.6×1012 cm-2 and 3.2×1010 cm-2, and interface state densities (Nss) of 1.6×1012 eV-1cm-2 and 6.5×1012 eV-1cm-2 were calculated for n and p-channel 2H-WS2 MIS structures, respectively. The data from these studies validate the hypothesis and demonstrate the potential of ZnO, a-BOxNy, and few layer 2H-WS2 for transparent electronics.