Results of experimental investigations on the relationship between nanoscale morphology of carbon doped hydrogenated silicon-oxide (SiOCH) low-k films and their electron spectrum of defect states are presented. The SiOCH films have been deposited using trimethylsilane (3MS) - oxygen mixture in a 13.56 MHz plasma enhanced chemical vapor deposition (PECVD) system at variable RF power densities (from 1.3 to 2.6 W/cm2) and gas pressures of 3, 4, and 5 Torr. The atomic structure of the SiOCH films is a mixture of amorphous-nanocrystalline SiO2-like and SiC-like phases. Results of the FTIR spectroscopy and atomic force microscopy suggest that the volume fraction of the SiC-like phase increases from ∼0.2 to 0.4 with RF power. The average size of the nanoscale surface morphology elements of the SiO2-like matrix can be controlled by the RF power density and source gas flow rates.

Electron density of the defect states N(E) of the SiOCH films has been investigated with the DLTS technique in the energy range up to 0.6 eV from the bottom of the conduction band. Distinct N(E) peaks at 0.25 - 0.35 eV and 0.42 - 0.52 eV below the conduction band bottom have been observed. The first N(E) peak is identified as originated from E1-like centers in the SiC-like phase. The volume density of the defects can vary from 1011 - 1017 cm-3 depending on specific conditions of the PECVD process.

We have studied the structural, optical and electrical properties of MOS devices, where the dielectric layer consists of a substoichiometric SiOx (x < 2) thin film deposited by plasma enhanced chemical vapor deposition. After deposition the SiOx samples were annealed at high temperature (> 1000°C) to induce the separation of the Si and SiO2 phases with the formation of Si nanocrystals embedded in the insulating matrix. The effects of the Si concentration in the SiOx layer and of the annealing temperature on the electrical and optical properties of these devices are reported and discussed. It is shown that by increasing the Si content in the SiOx layers the operating voltage of the device decreases and the total efficiency of emission increases. In fact, devices having an active layer with high Si concentration (46 at.%) annealed at 1100 °C, exhibit the best performances (i.e. the highest electroluminescence intensity and the lowest operating voltage). Furthermore, we have observed that by decreasing the thickness of the SiOx layer from 75 to 25 nm it is possible to strongly reduce the operating voltage down to 4 V.

Nd substituted bismuth titanate Bi4-xNdxTi3O12 were synthesized by sol-gel process and thin films were deposited on Pt substrate (Pt/TiO2/SiO2/Si) by spin coating. Thin films, characterized by X-ray diffraction and Raman spectroscopy, shows complete solid solution up to the composition x < 1. Initial results indicate that the ferroelectric polarization increases with increasing Nd content in the film with 2Pr = 50μC/cm2 for x = 0.46, which may have application in non-volatile ferroelectric memory devices.

A simple method, floating zone melting vapor, was used for fabricating nanowires of Si-Ge material. Single-crystalline nanowires were successfully synthesized. TEM images of these nanowires indicated that each nanowire consists of an inner single-crystalline core and an outer layer. An observation using high-resolution transmission electron microscopy (HRTEM) showed that almost all nanowires have a similar growth orientation to the crystalline core: [210]. The coexistence of germanium-self-catalyzed and oxide-assisted mechanisms has also been suggested.

Photoluminescence (PL) of Er3+ ions in nanocrystalline (amorphous) silicon matrix has been investigated under a high level of optical excitation. A superlinear increase of the PL intensity, a shortening of the PL decay time, and strong angular dependence were found at the excitation intensity above 200 kW/cm2. These effects are observed only in samples with presence of silicon nanocrystalls and explained by stimulated optical transitions.

This paper describes our recent research on the development of fully flexible and low-cost dye-sensitized nanocrystalline TiO2 solar cells (DSSC). At EIC Laboratories, we have developed various large-area solid-state versions, which include both ionically, and hole-conducting allpolymer DSSCs made by continuous coating and lamination process. Various critical steps involve ∼10 micron thick nanocrystalline TiO2 film deposition on conducting PET plastics by various methods such as spraying, spin coating, and screen printing, a low temperature sintering (∼150°C) process, and polymer laminated electrolyte have been demonstrated as valuable active components. The photovoltaic (PV) performance presented in this paper show the fabricated solar cells of ∼1.2 cm2 area with reproducible AM1.5 (Air Mass 1.5) efficiencies of 4.7%. A prototype solar cell with a new hole conducting star polymer with AM 1.5 efficiency ∼2.12% has been thoroughly characterized and discussed.

We resolved a photoemission signal from a single self-organized GaAs/Al0.3Ga0.7As quantum dot (QD) with picosecond time resolution. The emission spectra consisting of the multiexciton structures are observed to depend on the delay time and the excitation intensity. Through the analysis we can determine the carrier relaxation time as a function of population of photoinjected carriers. Enhancement of the intra-dot carrier relaxation is demonstrated to be due to the carrier-carrier scattering inside a single QD.

The process of formation of silicon nanoclusters in a silicate matrix by the focused electron beam of high power and their cathodoluminescent properties were studied in this paper. The size of the silicon clusters and their concentration depend on the electron beam power and on the properties of the silicate matrix (density, porosity, composition). In this paper we studied the evolution of cathodoluminescent properties in bulk silicon oxide, porous silicon oxide glass, silicagel (n·SiO2·m·H2O) and opal. The result of the modification of silica is the appearance of the CL bands at 2.3eV in green region, and the bands at 1.4 and 1.1eV. The CL intensity of these bands increases during the interaction with electron beam. The volt-ampere characteristics of the modified areas of the silica are non-linear and depend on the time of the interaction and the power of the electron beam. We relate the appearance of these new CL bands with formation of oxygen-deficit defects and silicon clusters.

The growth of Ge on Si(001) produces a wealth of morphologies of nanocrystals. After the deposition of a two-dimensional Ge film 3.5 monolayers thick, islands are formed, and several shape transitions can be observed depending on the growth temperature, rate and deposited thickness. In this work we combine atomic force microscopy and two different types of measurements of anomalous x-ray scattering to determine this elastic energy both in pyramid and dome shaped islands. By comparing pyramids and domes data, we have observed both an increase of lattice parameter and enhancement of interdiffusion for the domes. These results show that there is a drastic decrease of the elastic energy stored per atom upon this particular shape transition.

We show that two major carrier excitation mechanisms are present in II-VI self-assembled quantum dots. The first one is related to direct excited state – ground state transition. It manifests itself by the presence of sharp and intense lines in the excitation spectrum measured from single quantum dots. Apart from these lines, we also observe up to four much broader excitation lines. The energy spacing between these lines indicates that they are associated with absorption related to longitudinal optical phonons. By analyzing resonantly excited photoluminescence spectra, we are able to separate the contributions from these two mechanisms. In the case of CdTe dots, the excited state – ground state relaxation is important for all dots in ensemble, while phonon-assisted processes are dominant for the dots with smaller lateral size.

Electron charging and discharging processes in floating gate MOS memory based on nanocrystalline silicon (nc-Si) dots were investigated at room temperature using capacitance-voltage (C-V) and conductance-voltage (G-V) measurements. Sequential electron discharging processes from nc-Si dots manifest themselves clearly in G-V spectroscopy after charging of the dots. According to the conductance peak structure resulting from the Coulomb blockade as well as quantum confinement effects of nc-Si dots, electron-addition energy is estimated to be 50 meV. Taking the electron-charging energy between the silicon substrate and the floating dot (30 meV) into account, the quantum confinement energy is found to be comparable to the electron charging energy for an nc-Si dot of 8 nm in diameter embedded in the silicon oxide.

When Ge is deposited epitaxially on Si, the strain energy from the lattice mismatch causes the Ge in layers thicker than about four monolayers to form distinctive, three-dimensional islands. The shape of the islands is determined by the energies of the surface facets, facet edges, and interfaces. When phosphorus is added during the deposition, the surface energies change, modifying the island shapes and sizes, as well as the deposition process. When phosphine is introduced to the germane/hydrogen ambient during Ge deposition, the deposition rate decreases because of competitive adsorption. The steady-state deposition rate is not reached for thin layers. The deposited, doped layers contain three different island shapes, as do undoped layers; however, the island size for each shape is smaller for the doped layers than for the corresponding undoped layers. The intermediate-size islands are the most significant; the intermediate-size doped islands are of the same family as the undoped, multifaceted “dome” structures, but are considerably smaller. The largest doped islands appear to be related to the defective “superdomes” discussed for undoped islands. The distribution between the different island shapes depends on the phosphine partial pressure. At higher partial pressures, the smaller structures are absent. Phosphorus appears to act as a mild surfactant, suppressing small islands.

For the first time we use fluctuation electron microscopy to study the effect of electron irradiation on amorphous silicon. Before showing the results, we compare two variable coherence methods, hollow cone and dark field. These techniques have been successfully implemented in the Philips CM12, JEOL 4000 and Hitachi 9000 microscopes. The image fluctuations for ion-implanted and vacuum-deposited amorphous silicon can be reliably measured under the conditions used in these microscopes.

Si-rich SiO2, Nd-doped Si-rich SiO2 and Nd-doped SiO2 thin films were prepared. Photoluminescence (PL) spectra for visible and infrared were obtained for each as-deposited film. The samples were annealed by steps to different temperatures within the range 600°C-1100°C for 30 minutes at each annealing temperature. PL spectra were obtained at each step and their characteristics were studied. The best annealing temperature for the PL of the rare earth (RE) ions was obtained. The PL spectra of the films were compared with one another. Energy transfer from the silicon nanocrystals (Si nc) to the RE ions is verified using excitation wavelength and excitation power spectra.

Lamination of metal-coated elastomeric stamps against thin films of electroactive organics provides non-invasive, high resolution electrical contacts for investigations of charge transport in these materials. This approach uses the features of relief on the stamps to define, with nanometer resolution, the geometry and separation of electrodes that are formed by uniform evaporation of a thin metal film onto the stamp. Soft, room temperature contact of an element of this type with an organic semiconductor film on a gate dielectric and a gate yields a high performance top contact transistor with source/drain electrodes supported by the stamp. We review here our use of this approach to study the electrical properties of the organic semiconductor pentacene in thin film transistors structures. We also introduce a method for using the same techniques and structures to probe transport through organic monolayers.

Carbon-doped hydrogenated silicon oxide (SiOCH) low-k films have been prepared using 13.56 MHz discharge in trimethylsilane (3MS) - oxygen gas mixtures at 3, 4, and 5 Torr sustained with RF power densities 1.3 − 2.6 W/cm2. The atomic structure of the SiOCH films appears to be a mixture the amorphous SiO2-like and the partially polycrys-talline SiC-like phases. Results of the infra-red spectroscopy reflect the increment in the volume fraction of the SiC-like phase from 0.22 − 0.28 to 0.36 – 0.39 as the RF power increment.

Steady-state near-UV laser-excited (364 nm wavelength, 40±2 mW) photoluminescence (PL) has been studied at room temperatures in the visible (1.8 eV – 3.1 eV) subrange of photon spectrum. Two main bands of the PL signal (at the photon energies of 2.5 – 2.6 eV and 2.8 − 2.9 eV) are observed. Intensities of the both bands are changed monotonically with RF power, whereas the bandwidth of ∼0.1 eV remains almost invariable. It is likely that the above lines are dumped by the non-radiative recombination involving E1-like centres in the amorphous-nanocrystalline SiC-like phases. Such explanation of the PL intensity dependences on the RF power density is supported by results of experimental studies of defect states spectrum in bandgap of the SiOCH films.

With the introduction of high aspect ratio and steep geometries in deep-subquarter-micron dynamic random access memory (DRAM) device, it becomes more and more critical to understand the formation of undesired intermetallic Ti-Al phases in Al-metallization and thus better-control the profile of interconnectors. In this article, Ti-related inclusions in Metal 1 (M1) interconnecting layer (an AlCu-0.5% alloy) originated from the bottom Ti liner were characterized with an Analytical TEM. Samples were cleaved from nanometer 256Mbit dynamic random access memory DRAM devices. The TEM employed is a JEOL 2010F with a field emission gun (FEG) and running at 200KV acceleration voltage. Correlations among transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM), electron energy loss spectroscopy (EELS) elemental mapping, and x-ray energy dispersive spectroscopy (XEDS) elemental linescan were established. The results here not only provide important feedbacks to semiconductor product integration and optimization, but also demonstrate the full-functionality of the start-of-the-art analytical TEM in investigations of nanometer semiconductor devices.

For quantum-sized nanocrystalline silicon (nc-Si), various optical and electronic effects have been clarified in addition to a significant band gap widening. As typical examples of these induced effects, some emission properties of nanocrystalline porous silicon (PS) are described in this paper including the present status of application studies. The first one is electroluminescence (EL) of PS diodes. It is shown that following a drastic improvement in the external quantum and power efficiencies, stability has been significantly enhanced by the formation of covalent termination nc-Si surfaces. Next topic is the cold electron emission from PS diodes. When the nanostructure of the PS drift layer is appropriately controlled, injected electrons are accelerated ballistically toward the outer surface and emitted via tunneling through a thin-film top electrode perpendicular to the device surface as energetic electrons. As an efficient surface-emitting electron source, there are many advantages in this emitter over the conventional cold cathodes. The applicability of this emitter to either vacuum-type or solid-state flat-panel display is demonstrated. Finally, the usefulness of a PS device as a thermally induced ultrasonic emitter is presented on a basis of its fundamental characterizations. Technological potential of this emitter for functional acoustic devices is also discussed.

The sol-gel route using triethoxysilane as a precursor has been used to prepare films of Si nanocrystallites. These films were deposited on (001)-oriented silicon substrates either by spin coating deposition of a liquid phase that was further heat-treated under static vacuum (dots embedded in silica gel) or by vapour phase from the thermal decomposition under vacuum of the dried gels (uncapped dots). We address the structural characterisation of these samples and we find that a spontaneous orientation of the crystallites is obtained for heating treatment beyond 800°C if the dots are deposited in the vapour phase. The optical properties of dots embedded in silica gel reveal a strong red-orange photoluminescence due to carrier recombination at the dot surface, which is noticeably contaminated by oxygen and hydrogen.

We have studied the influence of overgrowth procedure and a few monolayer-thick AlAs overlayer on the properties of self-assembled InAs quantum dots (QDs) using scanning electron microscopy (SEM) and photoluminescence (PL). PL spectroscopy was used to optimize optical properties of the QDs by shape engineering (QD truncation) through adjustment of the thickness of overlayers and temperature of the subsequent heating. QDs with 6 nm - thick overlayer with subsequent heating up to 560°C was found to have the highest PL intensity at room temperature and the lowest FWHM, 29 meV. Ground state energy of the truncated QDs is very stable against variations of growth parameters. 1.23 μm edge-emitting laser of triple-layer QD structure demonstrated room temperature threshold current density, 74 A/cm2.