In the solid-state field-controlled emitter (SSE), the emission barrier, which is the factor of utmost importance for surface electron emission, is tailored by a controlled extrinsic parameter like the injected space charge located near the surface. This is done by depositing an ultra-thin wide band-gap semiconductor layer on a metallic surface. It is an alternative approach to the thermionic or field emission for which the work function value is intrinsic to the material used. The emission current measurements from the SSE cold cathodes show stable emission, at low applied field (≈50 V/μm) and in poor vacuum (≈10−7 Torr). The new emission mechanism has been modeled, the calculations and the theoretical analysis confirm the experimental results. The fabrication of the SSE, either by a sputter deposition in vacuum or by a sol-gel technique, meets most of the demands specific to high throughput fabrication of cold cathodes with large emitting area dedicated to applications in vacuum microelectronics.

To predict the optical power that could be harvested from light emission that is waveguided in the substrate of organic light emitting devices (OLEDs), a quantitative quantum mechanical model of the light emitted into the waveguided modes has been developed. The model was used to compute the exact distribution of energy in external, substrate and ITO/organic modes as a function of the distance of the emission zone from the cathode. The results are compared to the classical ray optics model and to experiments in two-layer OLED devices. Classical ray optics is found to substantially over-predict the light in waveguided modes.

This paper demonstrates that Sequential Lateral Solidification (SLS) of Si can be carried out on films as thin as – and potentially much thinner than – 250 Å. When compared to thicker Si films, however, the SLS-processed ultra-thin films contain more twins, and successful processing requires irradiation within a narrower laser energy density range and a smaller per-pulse translation distance. The physical interpretation of these findings is formulated by analyzing the details of the microstructures observed in single-pulse-irradiation-induced Controlled Super-Lateral Growth (C-SLG) experiments. SEM and TEM analyses reveal complicated microstructural details that we interpret as originating from breakdown of epitaxial growth during lateral solidification, an effect that is detrimental to the SLS process. Based on considerations of far-from- equilibrium solidification behavior of Si, it is argued that undercooling of the solidification interface below a threshold value at which solidification no longer proceeds epitaxially – arising from reduction in interfacial recalescence during lateral solidification of ultra-thin Si films, relative to that of thicker films – is responsible for the breakdown. Based on this model, we discuss how external parameters may be adjusted so as to permit optimal crystallization of ultra-thin Si films using SLS.

We present device-related experimental results that quantitatively reveal the effect of varying the active channel/grain-boundary misorientation on the resulting TFT characteristics. Specifically, using low-temperature SLS processes, we have fabricated and analyzed n-channel and p-channel devices (40 μm width × 8 μm length) with three different orientations of the channel with respect to the grain boundaries: parallel, 45° inclined, and perpendicular on Corning 1737 glass substrates.

The results reveal that the TFTs with the best (worst) characteristics were obtained for the devices with parallel (perpendicular) alignment. In general, for both n- and p-channel devices, the most prominent orientation-dependent effects were observed in the values of the field effect mobilities, which were 340, 227, and 141 cm2/Vsec for n-channel devices and 145, 105, and 80 cm2/Vsec for p-channel devices, in the order of increasing orientation mismatch. In contrast, no notable effect was manifested in the leakage currents, while small effects were seen for the sub-threshold slopes and threshold voltages. The degradation of device performance under hot-carrier stress was found to decrease with increasing orientation mismatch.

In this paper, an analysis of the high voltage induced degradation in top gate amorphous silicon Thin Film Transistors (TFT) will be shown, including the aspect of self-heating. It will be shown through experimental results that the degradation level under high voltages on drain and gate is different for TFT's with different channel lengths. In addition, the temperature distribution over the TFT area for devices with different channel length is simulated. Simulation shows that the peak of temperature distribution is located at the drain/channel edge and that level of thermal heating depends on the channel length.

We crystallize amorphous silicon (a-Si) layers (thicknesses: ∼300nm and ∼1300nm for comparison) that are deposited on glass substrates (Corning 7059) by low pressure chemical vapor deposition using a continuous wave Ar+-laser. We scan the raw beam with a diameter of ∼60νm in single traces and traces with varying overlap (30-60%). With optimized process parameters (fluence, scan velocity, overlap) we achieve polycrystalline Si with grains as wide as 100νm. The grain boundary population is dominated by first and second order twin boundaries as analyzed by electron backscattering analysis in the scanning electron microscope and convergent beam electron diffraction in the transmission electron microscope. These twins are known not (or only marginally) to degrade the electrical properties of the material. In addition to twins, dislocations and twin lamellae occur at varying densities (depending on grain orientation and process parameters). The recombination activity of the defects is analyzed by EBIC and according to these measurements crystallization receipts are defined that yield the reduction of electrically detrimental defects.

SrTiO3 crystals containing varying concentrations of Pr and Ga were grown by a standard floating zone method and their photoluminescence characteristics were investigated. It was found that only a small fraction of Pr ions added are incorporated in the lattice. When the Ga ions are co-doped, the solubility of Pr ions is increased considerably. Comparing the ionic sizes of the host and dopants, it seems that the increase of solubility of Pr by Ga co-doping is due to charge compensation achieved by the additional Ga3+. The addition of Ga in Pr - activated SrTiO3 resulted also in a considerable enhancement of Pr3+ emission band at 615 nm. This result is attributed to the hole trapping effect of Ga3+ ions.

Tin Oxide films of less than 30nm in thickness were developed as transparent conductive electrodes. The films were deposited onto glass substrates by APCVD. Fluorine was used as a doping component. Stability to heat treatments in air at more than 500• was studied. Carrier concentration decreased and Hall mobility increased by the heat treatments. It was found relations between carrier concentration and mobility exhibited an exponential relation in extremely low fluorine concentration films. The exponent of the relation was close to −1.5. Resistivity decreased for the films, while it increased for films with high fluorine concentration. It was also found migration of sodium from the substrates into the films increased with increase of fluorine concentration in the films. Results suggest the sodium migration would affect grain growth and electrical properties of the films.

A new fast fabrication method entailing, two step anodization of silicon with different HF solutions was used to form a high aspect ratio silicon Field Emitter Array on n-type silicon (resistivity of 0.01cm). A Silicon oxide mask was used to define the field emitter array. The silicon substrate was pre-anodized with low current density for 1 minute in the dark and then anodized in HF:H2O:Ethanol solution. Finally, the porous silicon was removed by isotropic solution etching. The turn-on voltage of the fabricated field emitters was approximately 27V/μm when the emission current density reaches 1μA/cm2. This compares with the turn-on field of about 35V/μm on silicon tip array fabricated by using an isotropic etching solution of HNO3. We obtained field emitter arrays with good uniformity and reproducibility.

We have applied junction capacitance and transient photocapacitance measurements to undoped tetrahedral amorphous carbon (ta-C)/silicon carbide (SiC) heterostructures to deduce defect densities and defect distributions in ta-C. The junction capacitance measurements show two thermally activated processes. One can be related to the activation of carriers out of defects at the ta-C/SiC interface while the other one with an activation energy of 0.36eV is an intrinsic property of the ta-C. The defect density at the ta-C/SiC interface is estimated to be roughly 9 ± 2 × 109 cm−2. The transient photocapacitance measurements have allowed us to observe the broader band tail of ta-C, giving a value (Urbach energy) of 230meV.

Epitaxial ZnGa2O4 and Sr2CeO4 thin-film phosphors were successfully grown on (100) MgO, YSZ, and SrTiO3 single crystal substrates using pulsed laser ablation. Cathodoluminescence efficiency was remarkably enhanced by adding lithium in the ZnGa2O4 and ZnGa2O4:Mn for both blue and green light emitting thin-film phosphors. The highest efficiencies, in this experiment, were 0.35 and 0.29 lm/W at 1kV for as-deposited blue and green zinc gallate phosphor films, respectively. In case of Sr2CeO4 films, the highest luminescence was 0.14 lm/W at 1kV and 0.26 A/m2 for films annealed at 1000°C in air.

Effect of nitrogen doping on field emission characteristics of patterned Diamond-like Carbon (DLC) films was studied. The patterned DLC films were fabricated by the method reported previously[1]. Nitrogen-doping in DLC film was carried out by introducing N2 gas into the vacuum chamber during deposition. Higher emission current density of 0.3∼0.4 mA/cm2 was observed for the films with 6 at % N than the undoped films but the emission current density decreased with further increase of N contents. Some changes in CN bonding characteristics with increasing N contents were observed. The CN bonding characteristics which seem to affect the electron emission properties of these films were studied by Raman spectroscopy, x-ray photoemission spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR). The electrical resistivity and the optical band gap measurements showed consistence with the above analyses. High-resolution transmission electron microscopic (HRTEM) results also support the formation of graphite-like phase in 9 at % N-doped DLC film.

It has been experimentally shown that the light trapping due to internal reflection from a smooth surface is reduced as the surface becomes progressively rougher. Although this phenomenon is qualitatively understood well, there has been a lack of detailed analysis of the scattering phenomenon which affects the light emission from thin film phosphors (TFPs). Factors which affect the light emission from the TFPs include electron beam-solid interaction (EBSI), film thickness, microstructure, surface recombination rate, surface roughness, and substrate (thus the interface formed). In many cases, they cannot be varied independently and thus making it difficult to interpret the results quantitatively. Furthermore, as the surface roughness is smaller or same as the wavelength of the emitted light, classical theories based on rectilinear propagation of the light cannot be used without gross simplification. A new theoretical model has been developed by incorporating diffraction scattering at the various interfaces and the factors mentioned above. The model provides an integrated solution to explain the cathodoluminescence (CL) properties of TFPs for field emission displays (FEDs).

Wide band gap semiconductors exhibit a low electron affinity and may prove suitable for cold cathode applications. We introduce a simple closed-form analytic approximation for the stability of electrons in the electron accumulation layer of planar Low Electron Affinity (LEA) semiconducting cathodes. This analysis extends our previous results, which used Runge-Kutta numerical integration of the linearized equations of motion for the electric potential and quasi Fermi level. The model shows conditions in which the electrons in the accumulation layer form a two dimensional array of regions of higher and lower electron density. This instability could lead to field enhancement without surface roughness and could account for observed electron emission at low applied fields.

Cold cathodes such as field emitter arrays offer the potential to benefit or enable space-based applications of critical commercial, government, or military importance by providing an electron source that is low power, low cost, requires no consumables, potentially robust as well as highly reliable. Applications that would especially benefit from such cold cathodes include low power electric propulsion (EP) thruster technology, electrodyanamic tethers (ED) for propellantless propulsion in low-Earth orbit, and spacecraft negative potential charge control. In controlled environments, field emitter arrays have shown substantial capability, but have failed in harsher environments more typical of space applications. We argue that a combination of localized arc suppression coupled with a low work function, but nevertheless robust, coating such as zirconium carbide would provide the needed ruggedness to withstand energetic ions, oxygen fluxes, and adsorbates typical of a spacecraft environment. We have found that arc-protected and coated FEACs that can operate in a 1-10 microTorr pressure environment with current densities of less than 0.1 Amps/cm^2 and gate voltages between 50-100 Volts, would enable reliable, lowcost devices capable of operating in the required space environment.

A hot-filament CVD reactor was used for the deposition of carbon nanotubes on substrates. Hydrocarbon or oxyhydrocarbon mixtures were used as the carbon source. Hot filaments at temperatures exceeding 2000C provided a means of dissociating the vapor or gas feedstock, heating the substrate, and allowing gas species to react in the gas phase as well as on the surface of the substrate leading to the deposition of desired carbon coatings. A high vacuum chamber was used to characterize the electron emission properties of these carbon nanotube coatings using a one-millimeter diameter tungsten rod with a hemispherical tip as the anode while the carbon nanotube coatings served as the cathode. The current-voltage characteristics of the carbon nanotube coatings were measured and used for calculating the electric field at which electron emission turned on as well as calculating the field enhancement factor of the carbon nanotubes. Field emission of electrons from carbon nanotubes starting from an electric field of as low as 1-2 volts per micrometer was achieved.

This paper addresses issues in the theory of field-induced electron emission. First, it summarises our present understanding of the theory of Fowler-Nordheim (FN) plots, and shows the relationship between a recent precise (in standard FN theory) approach to the interpretation of the FN-plot intercept and older approximate approaches. Second, it comments on the interpretation of FN plots taken from semiconductor field emitters. Third, it summarises the main points of a recent hypothesis about the mechanism of field-induced emission from carbonbased films and other electrically nanostructured heterogeneous (ENH) materials. Weaknesses in previous hypotheses are noted. It is hypothesised that thin films of all ENH materials, when deposited on a conducting substrate, will emit electrons in appropriate circumstances. Such films emit electrons at low macroscopic fields because they contain conducting nanostructure inside them: this structure generates sufficient geometrical field enhancement near the film/vacuum interface that more-or-less normal Fowler-Nordheim emission can occur. In connection with experiments on amorphous carbon films carried out by a group in Fribourg, it is shown that nanostructure of the size measured by scanning probe techniques should be able to generate field enhancement of the size measured in field electron spectroscopy experiments. This result provides a quantitative corroboration of other work suggesting that emission from amorphous carbon films is primarily due to geometrical field enhancement by nanostructures inside the film. Some counter-arguments to the internal-field-enhancement hypothesis are considered and disposed of. Some advantages of ENH materials as broad-area field emission electron sources are noted; these include control of material design.

Traditionally, organic light-emitting devices (OLEDs) are prepared with discrete layers for hole and electron transport. Different materials must be used for these layers because most materials will preferentially transport one charge carrier more efficiently than the other. In most cases, the emitter material serves a dual purpose as both the emitter and the hole or electron transporter. One of the major failure modes of OLEDs results from thermal instabilities of the insulating organic layers caused by joule heating during device operation. The problem is most pronounced for the hole transporting layer (HTL) material which are usually tertiary aromatic amines (i.e., TPD and NPD). This has been attributed to the relatively lower glass transition temperatures (Tg) and resulting inferior thermal stabilities compared to the other materials making up the device. Many researchers have produced HTL materials with higher Tgs based on tertiary aromatic amine oligomers and starburst compounds. Starburst or model dendritic materials offer the advantages of high thermal stabilities and multi-functionality.

Polycrystalline silicon thin film transistors (TFTs) were fabricated using laser crystallization of thin amorphous Si films grown by plasma-enhanced chemical vapor deposition. The films were exposed to a scanned XeCl excimer laser beam at 350 mJ/cm2. At this fluence the Si film com- pletely melted and crystallized in the form of uniformly distributed grains with an average size of 39 nm. One of the films was then subjected to a low fluence laser scan (250 mJ/cm2), which re- sulted in the melting of the top part of the film and lead to an increase in grain size. The TFTs fabricated without the partial melt method had good electrical properties and uniformities. The partial melt method lead to substantial improvements in most device characteristics, while the uniformity remained good.

A microwave plasma CVD reactor was used for the deposition of carbon nanotubes on substrates. Hydrocarbon or oxyhydrocarbon mixtures were used as the carbon source. Hot electrons in the microwave plasma at temperatures exceeding 10,000C provided a means of dissociating the vapor or gas feedstock, heating the substrate, and allowing gas species to react in the gas phase as well as on the surface of the substrate leading to the deposition of desired carbon coatings. A high vacuum chamber was used to characterize the electron emission properties of these carbon nanotube coatings using a one-millimeter diameter tungsten rod with a hemispherical tip as the anode while the carbon nanotube coatings served as the cathode. The current-voltage characteristics of the carbon nanotube coatings were measured and used for calculating the electric field at which electron emission turned on as well as calculating the field enhancement factor of the carbon nanotubes. Field emission of electrons from carbon nanotubes starting from an electric field lower than 1 volt per micrometer has been achieved.