In this paper we present a novel approach to fabricate single-electron devices utilizing different self-organization and self-alignment effects. Silicon quantum dots (QDs) are obtained employing reactive ion etching (RIE) into a silicon-on-insulator (SOI) substrate with a self-assembled etch mask. Electrodes with nanometer separation are fabricated and aligned to the QDs by means of a controlled electromigration process. The tunneling rates of the devices are defined by the native oxide covering the silicon QDs and can be adjusted by self-limiting thermal oxidation. The devices show clear Coulomb blockade behavior as well as Coulomb staircase features. In some samples also a gate influence is present giving rise to Coulomb diamonds in the differential conductance diagram.

This paper presents experimental results of the piezoresistance in p-type tensile strained silicon and compressive strained silicon germanium grown by molecular beam epitaxy (MBE) on (001) silicon substrates. The piezoresistance decreases in a tensile strained layer and increases in a compressive strained layer when compared to the unstrained material. The results show that one can tune the piezoresistance by tuning the strain in the piezoresistor and thus tailor the performance of the device. The obtained results show an increase in the piezoresistance effect of 35% in compressive strained silicon germanium and a decrease in the piezoresistance effect in tensile strained silicon of 24%. Furthermore, the results show that the piezoresistance of a tensile strained silicon crystal has a smaller temperature dependency compared to that of unstrained silicon. The piezoresistance effect decreases by 7% in tensile strained silicon compared to the piezoresistance effect decrease in silicon of 18% when changing the temperature from 30°C to 80°C.

Orange-emitting photoluminescent silicon nanocrystals have been grafted with pairs of compounds to produce a mixed monolayer on their surface. Vinyl acetic acid (VA) is used to enhance dispersibility in water by providing carboxyl termination, while alkyl groups are used to improve the stability of the photoluminescence (PL). The grafting of these molecules to the surface is enabled by an etching procedure that leaves a hydrogen terminated surface on the silicon nanocrystals. Multiple molecules can be grafted in series by taking advantage of the residual hydrogen present after initial grafting with a first compound. Multiple molecules can also be grafted in parallel by allowing them to compete for surface reactive sites and varying their concentration in solution to control the composition of the mixed surface layer. Both series and parallel grafting result in particles that have a mixture of two distinct molecules on their surface, and thereby allow control of the particle dispersibility in different solvents and the density of reactive groups for subsequent functionalization steps. Optimizing the surface composition may allow production of particles that can be reacted with proteins via carbodiimide linking chemistries while maintaining their PL and their dispersibility in water and buffer solutions. Here we focus on the parallel grafting approach.

Reliable fabrication of high-speed, delta-doped transistors and better understanding of two-dimensional metal-insulator transitions can be achieved using silicon molecular beam epitaxy (MBE). However, this fabrication technique should be performed with care, avoiding dopant segregation on epitaxial Si surfaces and improving the doping efficiency. Here we report comprehensive structural and optical investigations of MBE-grown Si/delta-doped Si:B multilayer structures. Measurements of Auger electron spectroscopy, Raman scattering, optical reflection and photoluminescence are performed. Our results indicate nearly metallic conductivity at room temperature with metal-insulator phase transition near T ∼100 K. In contrast to recently reported data, no enhancement of photoluminescence at room temperature is found. Occasionally, a few samples in specific areas exhibit strong photoluminescence at 1.4-1.6 micron attributed to structural defects, most likely due to B segregation.

The strain in the strained Si layer on a blanket strained Si/SiGe structure could not be determined with only convergent beam electron diffraction to high order Laue zone (HOLZ) line splitting. Combined with CBED and finite element calculations, we quantified the deformation field from HOLZ line splitting and demonstrated a procedure to determine the initial strain in the strained Si layer. Our results also gave us insights in strain relaxation in a TEM sample. The CBED technique combined with FE modeling has the potential for initial strain measurements on new generation short channel CMOS technology nodes.

Ge nanocrystals are formed in silica by ion beam synthesis and are subsequently exposed by selective HF etching of the silica. Under ambient conditions, the exposed nanocrystals are stable after formation of a protective native oxide shell of no more than a few monolayers. However, under visible laser illumination at room temperature and in the presence of O2, the nanocrystals rapidly oxidize. The oxidation rate was monitored by measuring the Raman spectra of the Ge nanocrystals in-situ. The intensity ratio of the anti-Stokes to the Stokes line indicated that no significant laser-induced heating of illuminated nanocrystals occurs. Therefore, the oxidation reaction rate enhancement is due to a photo-chemical process. The oxidation rate varies nearly linearly with the logarithm of the laser intensity, and at constant laser intensity the rate increases with increasing photon energy. These kinetic measurements, along with the power dependencies, are described quantitatively by an electron active oxidation mechanism involving tunneling of optically excited electrons through the forming oxide skin and subsequent transport of oxygen ions to the Ge nanocrystal surface.

We analyze a modern-day 65nm MOSFET technology to determine its electrical characteristics and intrinsic ballistic efficiency. Using that information, we then predict the performance of similar devices comprised of different materials, such as high-k gate dielectrics and III-V channel materials. The effects of series resistance are considered. Comparisons are made between the performance of these hypothetical devices and future generations of devices from the ITRS roadmap, including double-gate MOSFETs. We conclude that a Si channel device with a high-k gate dielectric and metal gate will outperform III-V channel materials for conventional CMOS applications, but will still not suffice in achieving long-term ITRS goals.

The channel of nanometre field effect transistor can act as a resonant cavity for plasma waves. The frequency of these plasma waves is in the Terahertz range and can be tuned by the gate length and the gate bias. During the last few years Terahertz detection and emission related to plasma wave instabilities in nanometre size field effect transistors was demonstrated experimentally. In this work we review the recent results on sub-THz and THz detection by 50-300nm gate length III-V HEMTs and Si MOSFETs. We present experimental results on the resonant and nonresonant (overdamped) plasma wave detection and discuss possible applications of nanometre field effect transistors as new detectors of THz radiations.

The paper reports on the synthesis and structural characterization of amorphous silicon oxide nanowires (SiONWs). The nanowires were prepared using the solid-liquid-solid (SLS) technique and display an average mean diameter in the range of 20-150 nm and 15-20 μm in length. Energy dispersive spectrometry (EDS) analysis revealed that the nanowires consist of Si and O elements in a ratio of approximately 1:2. The result was corroborated by the presence of a single peak at around 103 eV in the X-ray photoelectron (XPS) spectrum. As-prepared SiONWs display blue photoluminescence (PL) centered ∼ 400 nm. The blue luminescence is inhomogeneous with an increase in the PL peak intensity by a factor of 1.8 at certain areas of the surface. Next, we have investigated the effect of high-pressure water vapor annealing (HWA) on the PL and found that while the PL became homogeneous, a decrease of its intensity by a factor 2 was observed. The origin of the blue emission could be attributed to defect centers of oxygen deficiency in the wires.

In semiconductor epitaxy, a central challenge for the formation of ordered arrays of nanostructures, such as quantum dot islands, is the realization of processing routes to control surface-mediated growth mechanisms with high spatial precision and reproducibility across macroscopic lengths. To this end we have recently demonstrated a simple route for the directed assembly of heteroepitaxial islands based on rudimentary metal patterning. Here we show that the same metal patterns on the silicon surface that lead to island ordering radically modify island morphology resulting in shapes such as nanorods and truncated pyramids that are set by the choices of metal species and substrate orientation. These effects reflect a remarkable combination of metal-mediated growth phenomena that may be exploited to tailor the functionality of island arrays.

We have performed density-functional theory (DFT) and quantum Monte Carlo (QMC) calculations of the optoelectronic properties of hydrogen-terminated carbon nanoparticles (diamondoids). Both the QMC and DFT results show that quantum confinement effects disappear in diamondoids larger than 1 nm in diameter, which have optical gaps below that of bulk diamond. Furthermore, our QMC calculations predict a negative electron affinity for diamondoids up to 1 nm in diameter. Both these properties result from the delocalized nature of the lowest unoccupied molecular orbital.

Luminescent multilayers of SiGe nanocrystals embedded in an oxide matrix have been fabricated by Low Pressure Chemical Vapour Deposition of a-SiGe and SiO2 in a single run followed by a Rapid Thermal Annealing treatment. The diameter of the nanoparticles, the oxide interlayer thickness and the annealing conditions have been investigated in order to get the maximum intensity of the luminescence. The structures with small nanoparticles (3-4.5 nm) separated by thick oxide barriers (≈35 nm) annealed at 900 °C for 60 s yield the maximum intensity. These samples exhibit luminescence from 80 K to room temperature. An additional treatment at 450 °C in forming gas further increases the intensity of this luminescence.

Si and Ge nanocrystals were formed in alumina matrix by ion implantation and subsequent annealing. The phase separation of the Si nanocrystals was observed using X-ray photoelectron spectroscopy by monitoring Si 2p electrons. During nanocrystal formation with a high temperature annealing Si0 signals corresponding to Si nanoclusters increases while Si4+ signals related to a-SiO2 disappears from the spectrum. The transition from amorphous to nanocrystalline phase for both Si and Ge nanoclusters and the compressive stress exerted on the formed nanocrystals were also studied by Raman spectroscopy. Photoluminescence spectra of the Al2O3 containing nanocrystals were discussed by means of Ti and Cr impurities, as well as F centers. The existence of the amorphous Ge nanoclusters in alumina matrix significantly enhances the light emission of Ti3+ impurities.

We have investigated the stability of luminescence in pure water from a nanocrystalline silicon (nc-Si) particles passivated with various chemical elements such as a hydrogen, carbon and oxygen atoms. Each sample emitted red light with a peak wavelength in a range from 690 to 800 nm. When the hydrogen- and/or carbon-passivated samples were immersed in pure water, the intensity of red luminescence was decreased by aging after a short period of time. At the same time, the peak wavelength was also shifted toward shorter wavelength. These were caused by the generation of defects (Pb-centers) and the reduction of particle size due to the desorption of hydrogen and/or carbon atoms and the replacement from the Si-H and/or Si-C bonds to the Si-O bond, respectively, at the surface of nc-Si particles. On the other hand, the oxygen-passivated sample showed stable luminescence in addition to the slight blue-shift of peak wavelength under the immersion in pure water for 400 hours. The good stability was attributed to the formation of stable surface condition. These results are a strong indication that the stability of the luminescence in pure water can be remarkably improved by the oxygen-passivation to the surface of nc-Si particles.

Kinetic Monte Carlo simulations were performed to examine mechanisms underlying the formation of Si nanoparticles in Si-rich SiO2. We have determined two important features of the embedded Si nanoparticle growth: “coalescence-like” and “pseudo Ostwald ripening”. The former is mainly responsible for fast Si particle growth at the early stage of annealing where the particles are close to each other, while the latter becomes important when the density of particles is low such that they are separated by large distances. The pseudo ripening process takes place several orders of magnitude slower than the “coalescence-like” growth. The predominance of “coalescence-like” behavior in the growth of Si nanoparticles results in a big variation in the particle size in terms of the Si:O ratio. Overall the predicted growth behavior based on our Monte Carlo simulations agrees well with experiments.

We report crystallization of amorphous silicon films 50∼1400 nm thick formed on glass substrates by irradiation of an infrared semiconductor laser. Carbon particles with a mean diameter of 200 nm were uniformly coated on the silicon films as the optical absorption layer. Samples were irradiated with a 940-nm continuous wave (CW) semiconductor laser with a power of 20 W. A high optical absorbance 76.5% at 940 nm of the carbon particles layers resulted in annealing of silicon films by heat diffusion from the carbon particle layers. After removing the carbon particles layer, Raman scattering spectral measurements were carried out. A high scattering intensity and a sharp crystalline silicon phonon band were observed. The analysis of Raman spectra revealed a crystalline volume ratio almost 1.0. The analysis of the optical reflectivity spectra also revealed that the silicon films were crystallized in the whole thickness by the present method.

The preparation of nano-crystalline silicon suitable for optoelectronic purposes by plasma-enhanced hydrogenation is reported. The method is compatible with mature ULSI technology because of its low temperature and non-wet processing environment. Visible light emission with peak wavelengths ranging from blue to red has been observed and could be tuned by varying the processing conditions. While the blue light emission may be due to surface defects present in the oxide layer, the green and red light emissions are believed to be due excitonic emission within the nano-crystalline grains as a result of quantum confinement effects. The layers were studied by SEM, TEM, CL and FTIR. A LED was fabricated and electroluminescence demonstrated.

We find that in SiGe clusters grown on Si using Stranski-Krastanov (S-K) growth mode, (i) photoluminescence (PL) spectra, (ii) PL lifetime and (iii) PL thermal quench activation energies exhibit strong dependence on the excitation intensity. Under PL excitation intensity increasing from 1 to 104 W/cm2, the PL spectra exhibit blue shift from below Ge bandgap up to ∼970 meV. The PL lifetime shows strong dependence on the excitation wavelength, decreasing from 20 μs at ∼0.8 eV to 200 ns at ∼ 0.9 eV. The process of PL thermal quench has two clearly distinguished activation energies. At low temperature, small (∼15 meV) and excitation-independent activation energy is attributed to exciton thermal dissociation. At higher temperature, excitation-dependent PL thermal quench activation energy (increasing from ∼ 120 to 340 meV as excitation intensity increases) is found, and it is attributed to hole redistribution via tunneling and/or thermal ionization over the Si/SiGe valence band energy barrier.

We construct quasi-spherical Si nanocrystallites consisting of 17, 29, 47, 71, and 99 atoms with diameters from 0.8 to 1.6 nm embedded in an SiO2 network. All atoms have saturated bonds: Si is four-fold connected and O is two-fold connected. The models comprise 400-600 atoms and have lattice parameters of about 2 nm. The networks are subjected to a bond switching algorithm yielding models of nanocrystalline Si embedded in amorphous silica.

Subsequently, we employ density functional methods. As a result of the DFT-optimization we find that the Si nanocrystals are free of defects at the interface to the host matrix. Si-Si distances within the Si nanocrystallites are strained, the strain itself tailors off to the suboxide interface. The excess energy of the optimized models with respect to crystalline silicon and vitreous silica scales linearly with the surface of the Si nanoparticles. The interfacial energy of the nc-Si/SiO2 interface is calculated to 1.5 J/m2. We observe an increase of the band gap with decreasing cluster size due to the quantum-confinement effect. The highest occupied states of the valence band are located at Si-Si bonds close to the interface; the corresponding charge density forms a shell-like structure around the central core of the nanocrystal. The lowest unoccupied states are centered within the nanocrystal.

We have studied the biological properties of nanocrystalline silicon (nc-Si) particles after injection at various places in a mouse. The nc-Si particles with a size of 2.5 nm and a concentration of 1.3 mg/ml were dispersed in a normal saline solution (NSS). The NSS dispersible nc-Si particles were safely injected into the mouse. When the nc-Si particles in the NSS were directly injected into the subcutaneous vein and the coronary artery of the heart by syringe, the condition of bloodstream at each place was confirmed by the red luminescence (peak wavelength at 720 nm) from the nc-Si particles under the ultraviolet (UV) light-irradiation. Moreover, the nc-Si particles in the NSS, which were injected into the vein in the sole, smoothly flowed to the small intestine, and the smooth fluidity of nc-Si particles was also observed for the condition of the peristalsis of the small intestine. The nc-Si particles in the small intestine emitted red light during peristalsis under the UV light-irradiation. The red luminescence at each place was very bright and could be clearly seen with the naked eye. These phenomenons were achieved by the utilization of the harmless material, the formation of nc-Si particles with the single-order-size and the realization of the stable surface modification to the nc-Si particles.