Toshikazu Shimada

Chemical bonding states in the amorphous SixC1–x: H system studied by X-ray photoemission spectroscopy and infrared absorption spectra

Abstract XPS studies and infrared absorption measurements of the reactively sputtered (RS) amorphous SixC1–x: H alloy system have been made. The binding energy of the Si 2p core electrons decreases monotonically as the alloy composition x increases while the corresponding line-width remains almost constant. On the other hand, a curve of the C 1s core electron binding energy versus x has a kink at around x = 0·5∼0·6. Infrared absorption spectra reveal the existence of C–H, Si–H, Si–C bonds in the films. These results are discussed in terms of chemical bonding states.

Compositional and structural properties of amorphous SixC1−x : H alloys prepared by reactive sputtering

Amorphous SixC1−x : H alloys are prepared by simultaneous rf reactive sputtering of silicon and graphite in a H2‐Ar gas mixture. Silicon, carbon, and hydrogen contents are measured for the entire range of x by electron spectroscopy for chemical analysis (ESCA), Rutherford‐backscattering method, and thermal evolution of hydrogen. Evolution temperature dependence of the number of evolved hydrogen atoms is measured. The hydrogen‐evolution behavior and the optical gap are x dependent. These phenomena are discussed in the light of chemical‐bonding states.

Self‐organized fabrication of planar GaAs nanowhisker arrays

GaAs lateral nanowhiskers are grown on the side wall of a ridge formed on a GaAs substrate. The growth positions of the lateral nanowhiskers are controlled by a technique based on electron beam lithography. Also, lateral nanowhiskers bridging between two parallel wall surfaces are grown. These methods are potentially applicable to the fabrication of planar‐type quantum functional devices.

Electrical conductivity of disordered layers in GaAs crystal produced by ion implantation

The electrical conductivity of disordered layers in GaAs produced by ion implantation has been studied as a function of ion species, dose level, energy of implanted ions, and anneal temperature. The resistivity of the implanted layer, ρ, at room temperature can be expressed by a single relation, ρ=const×NDD−3, even for different masses and energies of implanted ions, where NDD is the total number of displacements of host atoms per unit volume due to nuclear collisions with implanted ions. At a temperature above 180 K the resistivity is proportional to exp(B/T) and below 180 K it changes as exp(B/T1/4). The conduction mechanism of the implanted layers is discussed based upon the hopping conduction in disordered or amorphous semiconductors. The annealing behavior of the implanted layers was also studied. The activation energy for recovery of the resistivity ρ was about 0.35 eV, which is quite small compared with the migration energies of stray atoms in ordered crystals. These results indicate that the impla...

Optical and electrical properties of amorphous silicon films prepared by photochemical vapor deposition

Amorphous silicon films have been prepared through mercury‐photosensitized decomposition of monosilane gas at low temperatures. The films show optical and electrical properties comparable with those of the best films prepared by plasma chemical vapor deposition. The feasibility of amorphous solar cells with short‐circuit current densities of more than 10 mA/cm2 has been demonstrated by fabrication of a Schottky barrier structure.

Site‐controlled growth of nanowhiskers

The metalogranic vapor‐phase epitaxy (MOVPE) growth of site‐controlled nanowhiskers having a single preferential growth direction is accomplished by using a SiO2 window mask. A small window size (200×200 nm in this experiment) is essential for growing a single whisker from a single Au‐ seed cluster formed inside each window of the mask. The presence of the SiO2 mask greatly influences the MOVPE growth process, especially the growth direction and resultant diameter of the whiskers. This influence may be due to surface migration of the source materials or source gas diffusion near the surface from the masked region to the window region.

Infrared Spectra of Amorphous Silicon-Fluorine Alloys Prepared by Sputtering in Fluorosilane-Argon Gas Mixture

Infrared spectra of amorphous Si : F alloys prepared by sputtering of a silicon crystal in SiF4 or a mixture of SiF4+Ar were measured in the frequency range of 450–4000 cm-1. Six absorption bands were observed in the 800–1100 cm-1 region. These bands are assigned as the SiFN (N=1, 2, 3) bond stretching vibration modes by comparison with the infrared spectra of SiFNH4-N molecules. In addition, fluorine modified or enhanced Si-Si bond stretching modes were observed at 515 and 650 cm-1.

Nanoelectromechanical nonvolatile memory device incorporating nanocrystalline Si dots

A nanoelectromechanical device incorporating the nanocrystalline silicon (nc-Si) dots is proposed for use as a high-speed and nonvolatile memory. The nc-Si dots are embedded as charge storage in a mechanically bistable floating gate. Position of the floating gate can therefore be switched between two stable states by applying gate bias. Superior on-off characteristics are demonstrated by using an equivalent circuit model which takes account of the variable capacitance due to the mechanical displacement of the floating gate. Mechanical property analysis conducted by using the finite element method shows that introduction of nc-Si dot array into the movable floating gate results in reduction of switching power. High switching frequency over 1GHz is achieved by decreasing the length of the floating gate to the submicron regime. We also report on experimental observation of the mechanical bistability of the SiO2 beam fabricated by using the conventional silicon etching processes.

Optical studies of deep‐center luminescence in CdS

Red luminescence in CdS has been studied in as‐grown and ion‐implanted crystals. An IR band consisting of two emission bands, IR1 and IR2, is produced by ion implantation. The higher‐energy band, IR1, has the same origin as the R band observed in some as‐grown crystals. A comparison of the R and IR1 bands in CdS with self‐activated (SA) luminescence in ZnS and GaAs shows that they are SA luminescence at 1.7 eV at low temperatures in CdS. The temperature variations in peak energy, half‐width, and intensity of luminescence are discussed, and the behavior is explained in terms of a configurational coordinate model. A vibrational energy of 0.025 eV, which is about 70% of the LO phonon energy in CdS, is calculated for the excited state of the center. The study of the excitation dependence of the center shows that the luminescence is due to an electronic transition within a localized center and not due to a donor‐acceptor pair recombination. The center has an excitation band about 0.22 eV below the band gap. Th...

Giant and high-resolution beam steering using slow-light waveguide amplifier

We propose a novel beam-steering device based on a slow-light waveguide amplifier. In this paper, we present the idea of this steering technique and show its modeling characteristics. Giant steering of the radiation beam is obtained by tuning the wavelength of input light, which is coupled into the Bragg reflector waveguide. A tunable deflection-angle range can be over 40 degrees. High beam coherency and flat intensity distribution enable us to obtain an ultra-large number of resolution-points over 1,000 for few-millimeter long devices.