As memory continues to be scaled to ever smaller dimensions, the floating-gate memory transistor, which offers a single-element storage cell, becomes more attractive. Typically, this structure has been reserved for nonvolatile applications, where the comparatively high voltages, slow write speeds, and limited cyclability could be tolerated. However, if the floating-gate, which is usually a continuous film of polysilicon, is replaced with a discontinuous film of small floating islands (nano-crystals), a new set of tradeoffs in these performance factors becomes possible, opening the door to broader applications. If these islands are further reduced to the point where Coulomb charging or energy quantization effects become relevant, it is possible to control the charge on the islands at a single (or few) electron level, which offers very low power operation and may enable new functionality. This paper will discuss design and fabrication of these memories, experimental results on fabricated devices, and modeling of what could ultimately be achieved, as well as what limitations will ultimately be reached.

Silicon single electron transistors (SET) with side gate have been fabricated on a heavily doped silicon-on-insulator (SOI) substrate. Samples demonstrate two types of characteristics: some of them demonstrate multiple dot behavior and one demonstrates single dot behavior in a wide temperature range. SETs demonstrate oscillations of drain-source current and changes in the width of the Coulomb blockade region with change of gate voltage at least up to 100 K. At temperature below 20 K long-term oscillations (relaxation) of source-drain current after switching the gate voltage has been observed in both multiple dot and single dot samples. Illumination affects both the characteristics of the SETs and the relaxation process. Telegraph noise has been observed in a definite range of source-drain and gate voltages.

We have used a variety of self-assembled monolayers as resists for low energy electron beam patterning. These compounds can be used as high-resolution patternable linker molecules for selected area binding of proteins and other organic compounds, as well as nanoparticles with organic chemical coatings. Because these systems can be aligned in registry to existing patterns, the organic systems may be positioned with the accuracy of electron-beam lithography. We have also explored the use of self-assembled monolayers for the creation of sub-wavelength artificial dielectric systems. The ultra-thin patterned monolayer is combined with a contrast-enhancing etch process to create high aspect ratio structures. This technique can be used to fabricate diffractive optical devices in a single-step process.

We studied the effect of surface roughness of Si wafers on porous silicon by means of photoluminescence (PL), Fourier transformed infrared (FTIR) absorption and Raman spectroscopy. We prepared several kinds of Si wafers with a different surface roughness, and then the anodization was performed at a same condition. PL spectra show a blue shift with the increase of surface roughness. The particle size of porous silicon nanostructure becomes the smaller with increasing surface roughness at the same time. On the other hand, FTIR absorption spectra show no difference regardless of surface roughness. The PL emission dependent on the surface roughness originates from a quantum size effect. We infer that the surface roughness causes the concentration of the current during anodization in the area where the radius of the curvature at the surface is small.

Porous silicon has been subjected to NF3/UV photochemical surface treatment in the range of 300-4000C. This treatment is found to enhance strongly the photoluminescence of porous silicon by couple orders of magnitude. The effect of photoluminescence enhancement has been observed only when the NF3 treated porous silicon was exposed to air environment. The photoluminescence intensity continued to grow with the aging time in air, even at the room temperature. Using atomic force microscope, scanning electron microscope and Auger measurements, it is found that the photoluminescence enhancement correlated with the formation of crystalline oxide layer at the porous silicon surface. This oxide layer SiOx (x≅2) is much more stoichiometric as compared to the native oxide SiOx (x≅1) covering the reference porous silicon surface (not treated by NF3). The rapid growth of the SiO2 layer is supposed to be due to the NF3/UV photo-thermal etching of the as-formed native oxide as well as to the cleaning and passivation of the porous silicon surface with fluorine.

We have fabricated the electroluminescence (EL) device using silicon (Si) nanocrystals, which were formed on Si substrate by co-sputtering of Si and silicon dioxide (SiO2). By treating with the Si nanocrystals in the hydrofluoric (HF) acid solution, the SiO2 region of the luminous layer reduced, and then, the electrons were efficiently injected in the Si nanocrystals. At the same time, Pb-center (non-radiative recombination center) was decreased by hydrogen termination to the Si-dangling bond in the interface between the Si nanocrystals and the SiO2 layer From these effects of the HF treatment, the high efficiency red light emission with the external quantum efficiency (EQE) of 0.35 % was obtained from the HF treated EL device under the operating voltage of +4.5 V.

We experimentally demonstrate that porous silicon optical microcavities can be effectively used as multi-parametric gas sensors. As known, the photoluminescence intensity and electrical conduction of porous silicon are strongly dependent on environmental properties, such as the dipole moment of molecules of surrounding gases. The sensitivity is large due to the large surface/volume ratio of porous silicon. While these effects can be observed in any porous silicon structure, microcavities of porous silicon allow an additional sensing parameter, i.e. the spectral position of the resonance cavity peak. The position of the peak depends on the index of refraction of the environment, and gives independent additional information. Moreover, we show that the dynamic response of the peak shift is much faster comparing the other sensing parameters. The combined effects on the peak position, luminescence intensity and electrical conduction can allow discrimination between different substances, and therefore porous silicon optical microcavities can work as multi-parametric optical/electrical sensors. We report detection of 1 ppm of NO2 and 500 ppm of ethanol at room temperature. With NO2, the electrical conduction increases and PL quenches, but the peak does not shift, whereas the peak shifts with ethanol (no significant PL quenching is observed at 500 ppm). This suggests that discrimination between different species can be achieved.

Control over the 1.5 µm emission from erbium is desirable for communication and computational technologies because the erbium emission falls in the window of maximum transmission for silica based fiber optics. Tunable, narrow, directional, and enhanced erbium emission from silicon based 1-D photonic bandgap structures will be demonstrated. The structures are prepared by anodic etching of crystalline silicon and consist of two highly reflecting Bragg reflectors sandwiching an active layer. The cavities are doped by electro-migrating the erbium ions into the porous silicon matrix, followed by high temperature oxidation. By controlling the oxidation temperature, porosity, and thickness of the structure, the position of the erbium emission is tuned to emit in regions where the normal erbium emission is very weak. The erbium emission from the cavity is narrowed to a full width at half maximum (FWHM) of 12 nm with a cavity quality factor Q of 130, highly directional with a 20 degree emission cone around the normal axis, and enhanced by more than one order of magnitude when compared to its lateral emission. Erbium photoluminescence (PL) from porous silicon 2-D photonic bandgap structures is also demonstrated.

We have studied chemical stability of thermally-carbonized porous silicon (PS). The initial hydrogen termination of PS has been replaced by carbon using thermal dissociation of acetelyne molecules. This kind of carbonized surface has been found to be at least as stable in humid atmosphere as a thermally-oxidized PS surface. It is also found to be stable in an aqueous KOH and HF. In-vitro studies of tissue compatible in simulated human fluid indicate improved stability and that the carbonized surface could be bioactive.

An improved analysis of the electrical transport parameters in meso-porous silicon is presented. Our approach is based on a separate contribution of the crystallites and their interconnections to the total impedance of meso-porous silicon layers. Meso-porous silicon morphology exhibits a columnar structure without quantum confinement. The electrical conduction is thus, partially due to the bulk conductivity within continuous paths of crystallites. The samples were realized on 0.02ω-cm p-type Si substrates. Porous silicon layers of 100µm of thickness and 50% of porosity were inserted in Al/SiO2/porous-Si/Si structures. Their electronic transport parameters were determined using complex impedance measurements. A frequency range of 102 - 107 Hz was used allowing an accurate determination of the impedance components. Combined with thermal stimulation, theses measurements provide a powerful tool for the interpretation of basic properties such as the carriers density in the crystallites and the trapping mechanisms. Our results were interpreted in terms of free carriers conduction in partially compensated crystallites prevailing at low frequencies. At high frequencies (above 10 kHz), the electrical conductivity is mainly controlled by hopping transport on localized states in the chaotic porous structure. Finally, the free carriers mobility, evaluated from SCLC measurement is discussed.

Micro-holes hundreds of μm-deep below the initial surface surrounded by 40- μm-tall micro-cones protruding over the initial surface form in silicon as a response to multiple UV pulsed-laser irradiation in an SF6 atmosphere. The micro-holes and micro-cones are arranged in a characteristic ensemble displaying a self-organized pattern. Similarly, deep-holes and micro-column ensembles form when the irradiation is performed in an oxygen-rich atmosphere. The formation mechanism of microcolumns and microcones in these reactive atmospheres has been studied using scanning electron microscopy, profilometry and x-ray diffraction. The growth of cones under SF6 atmospheres was studied in-situ using an ICCD gated camera coupled to a long distance microscope. The images obtained with the ICCD camera show that the fluorescent plume is correlated with the amount of ablated material. There is also a strong correlation between the plume and the growth of the cones. The cones grow in the region where the laser-generated plume is intense. When the flux of silicon-rich material ceases because the holes are very deep the balance between redeposition and ablation is tilted toward the latter and the cones begin to recede. Laser ablation is not only a function of the nominal fluence but also of the surface roughness and microstructure. These results strongly support the growth mechanism whereby laser-ablated silicon-rich molecules and clusters are transported to the tip and side of the cones by the laser- generated plasma.

We synthesized RF co-sputtered Eu2O3, Si and SiO2 on quartz substrates at different temperatures, and with and without the presence of H2 gas during sputtering. The photoluminescence of the samples was measured using both the 514.5nm green line and 457.9nm blue line of an Ar laser. The samples were then annealed, their luminescence remeasured, and the process repeated for a range of temperatures from 470°C to 1084°C. The effects of substrate temperature, presence or absence of H2, annealing, and the use of the green or blue line on the observed luminescence are presented.

We prepared a-SiOx (x < 2.0) films by co-sputtering Si and SiO2 targets and found that these films included nano-scaled a-Si regions in a-SiOx matrix. The structure of the films was evaluated by X-ray photoemission spectroscopy (XPS) and infrared absorption. The XPS spectra in the a-SiOx films showed two Si 2p peaks around 99.6 and 104 eV. This indicates that the a-SiOx films were composed of Si and a-SiO2 regions. The optical gap energy of this system rapidly increased when x exceeded 0.7. The rapid increase in the optical gap of this system indicates the formation of nanometer sized Si islands. The photoluminescence (PL) peak energy of this material decreased with increasing temperature above 60 K when x was less than 0.7. On the other hand, when x exceeds 0.7, the PL peak energy increases with temperature above 60 K. The quenching of PL intensity also takes place at 60 K. These results indicate a film structure change at x = 0.7, and recombination path and carrier distribution changes at 60 K. A correlation between film structure and PL properties are discussed. PL properties in this system are explained by superposition of the PL peak from nanoscale Si and a-SiO2 matrix.

We report a process for Silicon (Si) nano-crystal dots fabrication using a cold-wall Ultrahigh-Vacuum Chemical Vapor Deposition (UHV-CVD) system. Si2H6 gas was used as the pre-curser and irradiated upon SiO2 film on Si wafer to form Si nano-crystal dots.

In our system, nucleation, growth, and coalescence phases of nano-crystal dots on SiO2 were found to be related with the optical pyro-meter's read-out curve.

At first, the optimum gas irradiation time which gives the highest dot density without coalescence was decided for every gas irradiation condition by using an optical pyro-meter. Then, the dependence of optimum gas irradiation time, dot diameter and dot density on gas flow rate and wafer temperature were investigated. A decrease of wafer temperature or an increase of gas flow rate during the nucleation and growth phase results in a decrease of dot diameter and an increase of dot density. The optimum gas irradiation time was prolonged by decreasing wafer temperature or gas flow rate.

Finally, a reproducible process of forming non-coalesced, small size, and high-density Si nano-crystal dots of about 5.5nm in diameter with density of 1x1012 dots/cm2 were obtained. Typical process time to get such dot formation characteristics was about 10 minutes, which were long enough for ensuring reproducibility.

We present a detailed study of the electronics properties of individual silicon nano- crystals (nc-Si) elaborated by Low Pressure Chemical Vapor Deposition on 1.2 nm thick SiO2 grown on Si (100). The combination of ultra thin oxide layers and highly doped substrates allows imaging the hemispherical dots by Scanning Tunneling Microscopy. By analyzing the STM images, we deduce a size distribution, which ranges between 3 and 6 nm with a surface density around 1012 cm-2. Spectroscopic studies of single dots are made by recording the I(V) curves on the Si nanocrystal accurately selected with the metallic tip. These I(V) curves obtain on a single dot, exhibit Coulomb blockade and resonant tunneling effects. Coulomb pseudo gaps, Ec, between 0.15 and 0.2 V are measured for different dots. From the width and height of the staircases observed at bias greater than Ec, 60 meV and 40 pA respectively, capacitance of 0.5 to 1 aF and tunnel resistance of 3.5×108 and 5.7×109 Ohms are measured within the orthodox approximation for asymmetric junctions. We have determined, from experimental measurements, the energy of the first level confined in nc-Si.

The concept of a novel solid-state light-emitting device is proposed on a basis of our previous report that the nanocrystalline porous silicon (PS) diode with a well-controlled structure operate as an efficient ballistic electron emitter. This device is composed of a semitransparent thin Au film, a fluorescent thin film, a PS layer, and n-type Si substrate. When a positive bias voltage is applied to the Au electrode, visible luminescence is emitted of which band corresponds to that of the deposited fluorescent material. The optoelectronic characteristics suggest that the light emission is based on direct excitation of fluorescent film by ballistic electrons generated in the PS layer. This result indicates another possibility of nanocrystalline silicon for photonic applications.

We have studied carrier transport and lateral electrical properties of nanocrystalline Si layers containing size controlled Si nanocrystals. Using results from direct current (dc) and alternating current (ac) conductivity measurements, the charging of Si nanocrystals and Coulomb blockade effect are discussed.

Results are reported on the electron field emission properties of intrinsic and S- incorporated nanocrystalline carbon (n-C:S) thin films grown on molybdenum substrates by hotfilament CVD technique from methane-hydrogen (CH4/H2) and hydrogen sulphide-hydrogen (H2S/H2) gas pre mixtures respectively. The field emission properties for the S-incorporated films were investigated as a function of substrate temperature (TS). Lowest turn-on field was observed at 4.5 V/μm for one of the sample, which was grown at 900 °C, demonstrating the effect of sulfur addition. The S-incorporation also causes microstructural and structural changes, as characterized with ex situ techniques such as SEM, AFM and Raman spectroscopy (RS). Sassisted films show smoother surfaces and finer-grained than those grown without it. The electron field emission properties of S-assisted films is also compared to the film grown without it (intrinsic) at a particular deposition temperature and the turn-on field was found to be almost half for the S-assisted film than for the non S-assisted film. The influence of growth temperature was also conducted and an inverse correlation was found with the turn-on field (Ec). These studies were performed in order attempt to “tailor-the-material” as a viable cold cathode material by introducing the defecTS and altering the electronic structure.

Silicon nanowires containing a high density of copper atoms were prepared by laser ablation of Si/metal mixture targets at 1200 °C in argon gas flow. Copper atoms can gather in Si nanowires and precipitate into copper silicide nanocrystals distributed alone the wire axis. The diameters of the copper silicide nanocrystals increase with that of the host nanowire. The possible growth process of the composite nanowires was proposed.

It is demonstrated that a porous polycrystalline silicon (PPS) film is useful as a ballistic electron emitter for excitation source of a flat panel display. A 1.5 µ m polysilicon layer is deposited on a silicon substrate by Low Pressure Chemical Vapour Deposition (LPCVD) technique and subsequently anodised in an ethanoic HF solution and oxidised in a Rapid Thermal Oxidation (RTO) furnace. A thin Au film is deposited onto the RTO-treated PPS layer and used as a top electrode. The electron emission current Ie and the diode current Ips are measured as a function of the bias voltage Vps. Electron emission of which onset voltage is about 8 V rapidly increases with increasing Vps. The Ie value reaches about 2 mA/cm2 for Vps= 20 V at which the emission efficiency defined as Ie/Ips is about 1 %. The emission mechanism has also been investigated in terms of the correlation between the emitted electron energy and the structure of PPS layer. The observed energy distribution curve of output electrons suggests that the PPS layer acts as a ballistic transport medium and the emission occurs based on multiple tunnelling through silicon nanocrystallites. The PPS layer is also formed on the polysilicon layer deposited on a glass substrate by Plasma Enhanced Chemical Vapour Deposition (PCVD) technique. In this case, the film is treated by an electrochemical oxidation (ECO) in an H2SO4 solution. Similar emission characteristics are observed, although the emission current is lower than that formed on silicon substrate. We also demonstrate the 2.6 inches diagonal 53×40 pixels multicolour flat panel display. We name it ballistic electron surface-emitting display device (BSD). BSD shows the possible application to the future flat panel display.