Suzuka Nishimura

Variation of silicon melt viscosity with boron addition

The viscosity of silicon melts was measured by an oscillating cup technique. It has been found that the viscosity of silicon melts decreases by adding boron. The reduction of viscosity causes enhanced melt flow. This variation of melt flow enhances the chemical reaction between the silicon melt and the quartz crucible.

Surface Texturing of Silicon by Hydrogen Radicals

The surface texturing method for crystalline Si using hydrogen radicals generated by a tungsten hot filament was developed. We found that tungsten particles supplied from a tungsten filament work as an etching mask against hydrogen radicals. The surface morphology and feature size of the texture structure could be controlled by the particle deposition condition on the Si(100) surface. An inverted pyramid structure was obtained when the particle density was high, suggesting that the etching reaction induced by hydrogen radicals is anisotropic. The reflectance spectra of hydrogen-treated Si surface using this method showed a very low surface reflectance of less than 1% in the range from 200 to 900 nm without any antireflection coatings. The particles on the silicon surface can easily be removed using HF+HNO3 solution. This method is also effective for the texturing of Si(111) wafer, having a potential for the texturing of multicrystalline silicon.

Low temperature growth interface for growing Boron Monophosphide on Si substrates

Boron monophosphide (BP) thin layer has been grown on Si(100) surface by using low temperature growth process. The low temperature layer is an aggregate of small crystalline particles with small inclined angles to Si(100). This layer provides nucleation centers for growing BP layer. To elucidate the effect of BP layer, GaN layer was grown on BP/Si. It has been found that cubic GaN has been successfully grown on BP layer.

Silicon Whisker Growth Using Hot Filament Reactor with Hydrogen as Source Gas

Si whisker growth on a silicon substrate, using only pure hydrogen gas flow in a hot filament chemical vapor deposition reactor, has been studied by scanning and transmission electron microscopy. At the initial stage of the growth, tungsten–silicide particles are formed due to hydrogen radical etching by the filament. Simultanously the Si substrate exhibits a surface texturing. After long residence times of hydrogen gas in the reactor, silicon whiskers, with diameters between 10 and 50 nm, were observed on the textured silicon surface. Each whisker has a silicide particle at its tip. A mechanism of silicon whiskers growth using this method with hydrogen gas is proposed.

Growth of GaN on Si substrates using BP thin layer as a buffer

BP epitaxial layer has been successfully grown on silicon(100) substrates with a dimension of 10×10 mm2. The layer obtained is markedly flat and continuous. The thickness was 4.56 μm during 2 h growth process. To elucidate the possibility to grow a zinc blende GaN layer on BP, epitaxial growth of GaN has been carried out. A 100% cubic GaN was successfully obtained.

Characteristics of Ohmic Contacts to n-Type Boron Phosphide

We grew n-type boron phosphide (BP) (100) on a p-type Si(100) substrate by hydride vapor phase epitaxy. Electrical contacts are important for electrical evaluations and device applications, but the resistivity of ohmic contacts to BP has been little studied. We evaluated the contact characteristics for Al, Au, In, Ti, and Pt by annealing at temperatures in the range 300–500 °C for annealing times up to 50 min using a circular transmission line model pattern. Ohmic characteristics were obtained for the Al, Au, In, and Ti contacts. For the ohmic samples, we calculated the specific contact resistance ρc and observed a metal–BP interface by cross-sectional transmission electron microscopy. The minimum specific contact resistance ρc was 2×10-5 Ω cm2 for the Au/In/n-BP sample annealed at 500 °C for 50 min. For the present samples, thermionic-field emission is considered to be the dominant carrier transport process across the metal–BP interface.

Growth of c-GaN on Si(100)

Abstract One hundred percent cubic GaN with 2.5 μm thickness was successfully obtained on Si(100) substrates using BP thin buffer layer. BP buffer layer was grown on silicon(100) substrates with a dimension of 10×10 mm 2 . The dominant impurity in BP layer incorporated during epitaxial growth was silicon. The conduction type is readily varied depending on gas flow ratio BCl 3 /PCl 3 . GaN was grown of BP/Si(100) using trimethylgallium and monomethylhydrazine as a starting materials. The growth of BP and GaN and their characterizations will be discussed.

Si substrates texturing and vapor-solid-solid Si nanowhiskers growth using pure hydrogen as source gas

Scanning and transmission electron microscopies have been used to study silicon substrate texturing and whisker growth on Si substrates using pure hydrogen source gas in a tungsten hot filament reactor. Substrate texturing, in the nanometer to micrometer range of mono- and as-cut multicrystalline silicon, was observed after deposition of WSi2 particles that acted as a mask for subsequent hydrogen radical etching. Simultaneous Si whisker growth was observed for long residence time of the source gas and low H2 flow rate with high pressure. The whiskers formed via vapor-solid-solid growth, in which the deposited WSi2 particles acted as catalysts for a subsequent metal-induced layer exchange process well below the eutectic temperature. In this process, SiHx species, formed by substrate etching by the H radicals, diffuse through the metal particles. This leads to growth of crystalline Si whiskers via metal-induced solid-phase crystallization. Transmission electron microscopy, electron diffraction, and x-ray en...

Role of oxygen atoms in CaF2 crystals doped with Eu atom

The optical transparency in function of wavelength of CaF2 crystals doped with Eu (denoted by CaF2:Eu) has been measured. The optical absorption occurs below λ=400 nm depending on the amount of Eu atoms doped. The short wavelength below 400 nm has been shifted to around λ=425 nm. As a result, the 425 nm wavelength increased and the light below 400 nm was cut through CaF2:Eu crystals. This scintillating effect has been found much increased by adding oxygen atoms in crystals. This is due to the distortion of electrical and structural symmetry in crystals by adding oxygen atoms in the form of oxide materials.

Effect of Si Doping on the Crystal Structure of HVPE Grown Boron Phosphide

Boron Phosphide (BP) layers have been grown on Si (100) as a substrate for cubic GaN heteroepitaxy. Si heavy doping was attempted to reduce the threading dislocation density in the BP. To observe the effect on dislocations in BP by Si doping, we used cross-sectional transmission electron microscopy (XTEM). Also, Glow Discharge-Optical Emission Spectroscopy (GDOES) were used to evaluate the effect of Si doping. For the samples under the conditions (a) and (e), we found the formation of pits at BP surface and an increasing in the proportion of threading dislocations with an angle of 90 ° to the surface. We could not see a significant change in the threading dislocation density by Si doping under the conditions used in this paper.