Light emitting devices (LEDs) based on porous polysilicon (PPS) have been fabricated on a transparent quartz substrate. Several structures have been developed, each consisting of a backside contact (ITO or p+ polysilicon), a light emitting PPS layer, a capping layer, and a metal top contact. Photoluminescence (PL) from PPS is similar to that of etched crystalline Si, peaking near 750 nn and showing degradation during 515 nm laser excitation with intensity <100 mW/cm2. This degradation disappears if PPS is oxidized after formation. Visible electroluminescence (EL) has been achieved in both oxidized and non-oxidized PPS devices with voltages under 10 V and current densities <200 mA/cm2.

Very high frequency (100 MHz) hydrogen plasma treatments on a-Si:H deposited by plasma enhanced chemical vapour deposition were studied. Ex-situ optical measurements have shown that etching and chemical transport occur as competing phenomena. The one that prevails is determined by the plasma conditions. In particular, very efficient chemical etching is observed for high H2 flow rates, while, for low H2 flow rates, the equilibrium is shifted toward deposition, and a structural modification of the sample is observed. The experimental conditions were stressed in the direction of utilizing chemical transport from the cathode to deposit very thin (7 nm) microcrystalline films with a pure H2 plasma.

The refractive index change of polariton propagation in a GaAs quantum-well waveguide was measured as a function of the electric field. Its temperature dependence was also measured. The experimental results showed that the refractive index change of the polariton propagation was at least three times as large as that of the conventional light propagation. This effect remains up to 40 K, and coincides with the temperature dependence of the rate of polariton scattering by phonons. We also Fabricated directional-coupler-type switching devices to apply this large refractive index change, and were able to demonstrate the operation in a single quantum-well waveguide. Our results indicate that extremely small and low driving voltage switching devices may be feasible.

Morphological characterization and the nonlinear optical properties of laser ablated germanium nanoclusters are discussed in this paper. Laser ablated films contain micron sized droplets that are composed of nanoclusters. The clusters have cubic and tetragonal symmetry. Results from TEM, AFM, and XRD are presented for the surface characterization. Nonlinear absorption is observed at very low light intensities and nonlinear absorption and refraction are seen at peak light intensities of 18 KW/cm2 at λ. = 532 nm. The estimated change in refractive index is 0.05 at these intensity levels.

A new fabrication technique for quantum dots is proposed on the basis of theoretical studies. It is known that the self-limiting phenomena of silicon oxidation are governed by the large stress induced by the volume expansion. We estimated the change in the band parameter of the silicon under the stress induced by the oxidation. The results show that the band-gap of the silicon considerably decreases under two-dimensional compressive strain. Accordingly, introducing strain to a small part of a Si wire results in the formation of a “strain-induced effective quantum dot”. Moreover, we also propose theoretically a new procedure for fabricating a silicon single electron transistor by the combination of silicon oxidation and nitridation techniques.

Electron beam excited plasma (EBEP) CVD is a novel fabrication route for poly Si. Deposition was carried out on Si and SiO2 layer from pure SiH4 without hydrogen dilution. Crystalline silicon (μc-Si:H) films were made with electron acceleration voltage, discharge current, source gas flow rate, chamber presser, substrate temperature varied systematically. Average grain size was about 10 nm. Crystalline ratio was up to 0.7 at the maximum. The films contain about 19 at% hydrogen in spite of no dilution. It is considered that EBEP supplies much about atomic hydrogen due to the high decomposability of the source gas.

Pressure induced structural phase transformation in nanocluster assembled GaAs is studied using parallel molecular dynamics simulations in the isothermal-isobaric ensemble. In this system the spatial stress distribution is found to be inhomogeneous. As a result structural transformation initiates in the high stress regions at the interface between clusters. Structural and dynamical correlations in the nanophase system are characterized by calculating the spatially resolved bond angle and pair distribution functions and phonon density of states and comparing them with those for a single cluster and bulk crystalline and amorphous systems.

Room temperature current-voltage (I-V) characteristics were studied across the thickness of the Ge nanocrystalline films, prepared by the cluster beam evaporation technique. The films thus prepared are deposited either at room temperature (Ge-RT) or at liquid nitrogen temperature (Ge-LNT). Ge-LNT nanofilm is subjected to oxidation while Ge-RT did not get oxidized. Steps were observed in the I-V characteristics of the thin Ge- LNT samples suggesting the Coulomb Blockade effect.

In this paper we demonstrate that porous silicon (PS) can be used as an immobilization matrix and a transducer for biosensor applications. Thin layers of PS were fabricated showing fine structure in their reflection spectra, characteristic of longitudinal optical cavity modes, or Fabry-Perot interference fringes. The PS surface was modified by covalently bonding streptavidin to a heterobifunctional linker immobilized to the surface using common silane chemistry. The mode spacing and wavelength in the interference spectrum was modified, by displacing buffer and introducing proteins into the PS layer. Protein-protein interactions between immobilized Streptavidin and biotinylated Protein A followed by Protein A and IgG were detected. The surface was regenerated during the course of the experiment showing reversibility of the sensor at the third layer.