We have fabricated and analyzed high quality InGaAs/InP quantum wires by electron beam lithography and wet chemical etching. In order to optimize the shape of the wet-etched wires different wire orientations were investigated. As results of the lithography process we obtain wire masks with widths down to 15 nm and etched wires with widths of the InGaAs layer of 18 nm.

The wires were studied optically by means of photoluminescence spectroscopy. In contrast to dry etched wire structures the wet chemically etched wires show strong optical emission even for geometrical widths less than 25 nm. The weak decrease of the quantum efficiency with decreasing wire width indicates that there are no dead layers at the side walls of the wires, which is in contrast to previous studies on dry-etched structures. The photoluminescence energy of the InGaAs/InP wires is independent of the wire dimension down to widths of 50 nm. This indicates that a steep lateral potential in our structures is obtained due to the confinement by the semiconductor/vacuum transition at the etched surfaces. For wires with smaller widths an increasing blue shift of photoluminescence energy up to more than 30 meV is observed.

A general method is presented for calculating the spatial distribution of damage generated by localized implantation in semiconductors. Implantation through masks and focused ion beam implantation in GaAs are simulated and compared to cross-sectional transmission electron microscopy observations. An excellent agreement is obtained when a depth-dependent lateral straggle is considered. Arbitrarily shaped mask edges and different compositions for the mask and the substrate are included in the calculations as well as realistic current profiles of the ion spot in the case of focused ion beam implantations. Simulations and experiments clearly demonstrate the potential application of localized implantations to fabricate lateral quantum nanostructures.

A new approach has been taken for the fabrication of Quantum Dot materials to be used for physics as well as for opto-electronics applications. We used a generation technique of ultrafine aerosol Ag particles which are deposited onto the surface of GalnAs/InP quantum well structures grown by Metal Organic Vapor Phase Epitaxy (MOVPE). The particles, ranging in size between 30 and 40 nm, are subsequently used as an etching mask. The Ag aerosol produced by homogeneous nucleation and can have a mean diameter in the range 2 – 100 nm. After size-selection, monodisperse particles with a very narrow size distribution are deposited onto the semiconductor surface at a density of about 109 cm-2. Low energy CH4/H/Ar Electron Cyclotron Resonance (ECR) plasma etching results in the formation of free-standing InP columns 50 to 80 nm in diameter and 120 to 280 nm in height. Their size and stability were found to be dependent on the etching conditions and the diameter of the particles. Low-temperature cathodoluminescence (CL) was used to evaluate the quantum dot structures fabricated by this technique.

Experimentally observed blue shifts of the peak position of the luminescence from quantum-well-wire and -dot structures are often significantly larger than the calculated shifts induced by lateral confinement in the structures. In this work we have used high-quality InGaAsAnP multi-quantum-wells for the fabrication of wires. The quantum wells are in the range 3 to 17 monolayers (ML) nominally. The thinnest well, 3 ML, shows a clearly resolved split into two luminescence peaks from areas with a thickness difference of 1 ML. In the case of the wires, the luminescence from the thicker wells show a blue shift, as well a significant broadening. However, the thinnest well shows no blue shift, but a different ratio of the two peaks, with the high energy peak favoured in the wire case. We interpret these effects in terms of a reduced transfer of excitons from thinner to thicker areas of the well in the wire as compared to the unpattemed areas. This due to a reduction of the transfer from 2 dimensional to 1 dimensional in the wires. The peaks originating in areas of different ML thicknesses are not spectrally resolved in the thicker wells and the reduced transfer therefore results in a blue shift as well as a broadening of the luminescence peak.

Experimental photoluminescence spectra of GaAs microcrystals show pronounced variations compared to the luminescence of bulk GaAs. The observed spectra are explained by spectral enhancement and inhibition of spontaneous emission in a three-dimensional optical resonator formed by a dielectrically confined semiconductor microcrystal. The crystals were produced by pulverization of bulk GaAs, size-separated by sedimentation techniques, and characterized by transmission electron microscopy, electron diffraction and x-ray diffraction.

Scanning tunneling microscopy (STM) and reflection high-energy diffraction (RHEED) have been employed to investigate the morphology of faceted GaAs(001) surfaces grown by molecular beam epitaxy (MBE). The RHEED pattern monitored during the growth indicates that the faceting corresponds to (711)A planes. The STM images obtained on these surfaces reveal predominantly a (2×4) local ordering, although unusual (2×3) and (2×6) structures have also been observed. The atom-resolved imaging of the (2×4) structure indicates that the unit cell consists of two As dimers and two missing dimers, identical to the structure obtained on the flat As-rich GaAs(001)-(2×4) surface. Furthermore, islands on the surface are found to be anisotropie, with a shape anisotropy of about 4:1 for step A to step B. The anisotropy is explained in terms of the difference in step edge reactivity.

The configurations of misfit dislocations in In0.2Ga0.8As/GaAs(001) hetero structures grown on slightly misoriented substrates was investigated by transmission electron microscopy (TEM). Layers 6 nm, 20 nm and 40 nm thick were grown by MBE. The substrate was tilted in [110], [110], [120], [210] and [010] directions at angles between 0° and 10°. Only in the 40 nm thick layers networks of 60° and 90° dislocations were formed. Misfit dislocations were found at the interface in <110> directions. In the substrate tilting range between 0° and 4° the changes in dislocation density can be explained by the different

character of α and β dislocations. For a substrate tilting above 6° the different dislocation sets show an increased anisotropy. The misfit dislocations at the interface were decorated by In atoms. The influence of three-dimensional crystal growth on increasing surface roughness is discussed.

Numerous GaAs epitaxial microcrystals having nearly equal size were fabricated on a S-terminated GaAs(001) surface by a sequential supply of Ga and As molecular beams. The GaAs(001) surface was terminated by sulfur atom in the MBE chamber. The growth of GaAs epitaxial microcrystals is caused by a Vapour-Liquid-Solid(VLS) mechanism. GaAs epitaxial microcrystals were also fabricated on a S-terminated GaAlAs(001) surface by the same procedure.

We have investigated the optical properties of wet chemically etched InP/InGaAs-wires and dots with widths between 100 nm and 10 μm for different excitation densities. We observe that the non radiative recombination centers at the etched sidewalls can be saturated already at moderate excitation densities about 100 W/cm2. Avoiding saturation effects we obtain a surprisingly large sidewall recombination velocity of 107 cm/sec at 77 K. The comparison of wire and box structures shows that there is no significant difference in the quantum efficiency of both types of structures down to a geometrical size of 160 nm.

The intra-and intersubband scattering rates for emission and absorption of longitudinal optical (LO) phonons by electrons confined in a cylindrical GaAs-GaAlAs quantum wire are calculated. Multiple peaks due to intersubband transitions appeared on the total scattering rate as a function of the electron energy.

The interaction of quasi-one-dimensional electrons and longitudinal-optical (LO) phonons, placed in a perpendicular magnetic field is calculated. Results are presented for the polaron correction to the Landau levels and the polaron cyclotron mass.

Synthesis of CdSe quantum dots with a high degree of monodispersity is achieved by nucleation from a supersaturated solution followed by growth to the desired particle size. The effects of temperature on the kinetic mechanisms of nucleation and growth were observed. A reaction vessel equipped with a low thermal mass internal heating element enabled controlled ramping of the solution temperature during the reaction. Nanocrystallite diameter is determined by the reaction time and the solution temperature during particle growth.

A method was developed to fabricate ∼1μm thick glass films containing ∼3 vol% CdSe quantum dots. A sol was prepared by mixing a silica organosol with a nanocrystallite dispersion of CdSe and was applied to amorphous quartz substrates by spin-coating. The sols were dried at elevated temperatures in a nitrogen atmosphere. Optical absorbance and fluorescence measurements of the glass film were used to characterize the optical properties of the embedded nanocrystallites. Comparison of the excitonic absorbance of the quantum dot dispersion and the doped glass film shows that particle monodispersity is maintained upon incorporation into the dielectric matrix. Stokes shifts in the band-to-band fluorescence relative to the film absorbance were measured. Shifts in the wavelength of the excitonic absorbance and fluorescence were observed upon incorporation of the quantum dots into the glass film and upon heat treating the glass film to elevated temperatures.

Quantized CdS particles of about 60 A in diameter were prepared by an organo-sol method in the presence of PVP (poly(N-vinyl-2-pyrrolidone)), and this new method could make the CdS ultrafine particles densely dispersed in PHEMA (poly(2-hydroxyethyl methacrylate)) host films. The values of | x(3) |/α (third-order optical nonlinear susceptibility per unit absorption coefficient) were obtained (2.0 × 10-10 esu· cm at 460 nm and 2.7 × 10-10esu · cm at 470 nm) using a nanosecond DFWM technique. An enhancement of non-linearity was observed for the first time when Ag particles or Ag+ ion were co-dispersed with the CdS particles in small amounts. The addition of 8.57 wt% Ag particles, or 4.28 wt% Ag+ ion in the ratio to CdS made | x(3) |/α enhanced to be 3.9 × 10-10 esu· cm, or 4.1 × 10-10 esu· cm, respectively. The surface modification by the formation of Ag2S on the surface of CdS colloids is believed to be responsible for this enhancement.

Nanometer size semiconductor particles coated with another semiconductor can exhibit unusual and interesting phenomena associated with the redistribution of the electron and hole wavefunctions. Using the band offsets and effective-masses, the band gap as well as the wavefunctions can be altered by changing the core radius of the particles. CdS/PbS coated semiconductor nanoparticles are synthesized by ion displacing method and experimental results are discussed along with the theoretical calculation. Optical absorption as well as TEM, Electron diffraction results provides for the evidence that the particles are coated.

We have prepared compounds having the general formula M(SR)2 (M = Zn, Cd; R = i-Pr, t-Bu, Bz) and Hg(SR)CI (R = i-Pr, Bz) and investigated their use as potential sources in the preparation of metal sulfides from molecular precursors. Selected examples of the prepared compounds have been studied by single crystal x-ray diffraction. Decomposition has been carried out both in the solid state and by heating a suspension of a metal thiolate in a high boiling hydrocarbon. The decomposition products have been studied by GC/MS (liquids) and XRD (solids).

We present photoluminescence excitation spectra for glasses doped with CdSxSe(1-x). The peak of the emission spectrum is blue shifted toward the bandgap as excitation energy flux is increased. Total photoluminescence emission intensity is observed to be significantly enhanced and blue shifted by exciting with photon energies greater than ∼4 eV. A simple model of the nanoparticle band structure is presented to account for the observed spectra.

Metal-coated particles of nanometer dimensions can exhibit unusual optical properties due to the local-field enhancement mechanism. However, the properties are affected by uncontrollable factors that degrade the expected performance. In this paper we report theoretical results of coating thickness variations and diffuse interface effects on the optical absorption and the nonlinear optical response of particles with a CdS core and a silver coating. The linear and nonlinear optical properties are discussed within the context of the effective medium theory for small volume fractions.

Polycrystalline diamond film (PDF) is known for its high power, high temperature, and radiation hard potential. The interest in piezoresistivity of PDF is that it is a candidate for high temperature sensing (e.g., pressure sensor).

Piezoresistivity measurements were taken of boron-doped PDF grown by microwave-plasma chemical vapor deposition(CVD). Three substrates, silicon, aluminum nitride and tungsten were used. Films were detached from these substrates, then attached to a ceramic substrate. The piezoresistivity varies, dependent on the original host substrate. For example, at room temperature, the PDF film from tungsten has a greater gauge factor, around 75. The carrier activation energy of this film, determined from log R(l/T), was nominally 0.25eV.

Combining thick film technology and CVD processes, patterned B-doped PDF has been achieved monolithically on A1N substrates. The characteristics of this configuration is being investigated and will be presented.

Si/βFeSi2/Si (100) and (111) structures were obtained by implantation of 450 keV Fe+ ions with a dose of 6×1017 Fe+ ions/ cm2 into Si substrates. A continuous buried βFeSi2 layer with thickness of 250 nm was formed during subsequent annealing. By transmission electron microscopy it has been found that for (100) Si the layer consists of βFeSi2 grains with lateral dimensions of approximately O.5 μm and for (111) Si of grains of 5 μm in size. The βFeSi2 films exhibit a high degree of epitaxy with the Si substrate. A detailed structural examination shows the occurrence of several epitaxial relationships of βFeSi2 with the Si substrate. In contrast to two-dimensional surface growth techniques, the formation of a buried layer by implantation occurs by a three-dimensional growth process by the coalescence of βFeSi2 precipitates. The different orientations of the βFeSi2 grains in the buried layer are already established by the orientation of the precipitates formed during implantation.

Indium doped zinc oxide films have been deposited from diethyl zinc, ethanol and trimethyl indium in the temperature range between 225°C and 450°C in a laminar flow atmospheric chemical vapor deposition reactor. Both doped and undoped films were crystalline. The doped films have electron density up to 9×1020 cm-3, conductivity up to 850 Ω-1cm-1, and mobility up to 8 cm2/Vs. The indium doping increases the average visible absorption from less than 1% to above 20%. The transparency and conductivity of indium doped zinc oxide films are lower than those of fluorine doped films.