Shiro Karasawa

Growth of diamond thin films on silicon and TEM observation of the interface

Abstract Diamond thin films have been synthesized on silicon substrates by electron assisted chemical vapour deposition (EACVD). The influence of conditions of synthesis on the crystallinity of the films was examined by laser Raman spectroscopy. From these results, the optimum conditions for synthesis were determined. Transmission electron microscopy (TEM) was used to observe film/substrate interfaces of films which were synthesized under optimum conditions. An amorphous intermediate layer was observed between the silicon substrate and the diamond film.

Effect of ion implantation and surface structure of silicon on diamond film nucleation

Abstract Effect of ion implantation and scratch of silicon on diamond film nucleation has been studied. After the Si substrate was scratched, 100 keV Ar + ions were implanted. Diamond film was deposited on the implanted Si. Nucleation density decreased as the dose amount was increased. When the dose amount was greater than 3X10 15 ions/cm 2 , almost no diamond particles had grown on the implanted area. The reason why ion implantation on Si substrates causes a decrease in the nucleation density was examined by reflection high-energy electron diffraction (RHEED), atomic force microscopy (AFM) in air and Rutherford backscattering spectrometry (RBS).

Spectral response of a photodiode using 3C-SiC single crystalline film

Abstract 3C-SiC/Si heterojunction photodiodes and 3C-SiC homojunction photodiodes have been fabricated by atmospheric chemical vapor deposition. The maximum quantum efficiency of heterojunction photodiodes with a window layer of 10 μm thick is 80% at 550 nm. An increase in the thickness of the SiC layer reduces the responsivity in wavelength regions shorter and longer than 500–550 nm. 3C-SiC self supported films of 20 μm thick, epitaxially grown on Si, have been used as substrates for homojunction photodiodes. The responsivity of the homojunction photodiode with a window layer thickness of 0.5 μm is 72 mA/W at 250 nm with a quantum efficiency of 36%. When the thickness of the window layer is decreased, the peak responsivity increases and the peak wavelength shifts to a shorter wavelength. These spectral responsivities are discussed together with the results of calculations using a one-dimensional model.

DIAMOND CRYSTAL GROWTH ON SILICON AND ITS INTERFACIAL CHARACTERIZATION

Abstract Diamond crystals have been grown on an amorphous buffer layer formed on silicon substrates using electron-assisted chemical vapor deposition using tantalum filaments and gas fed by the natural circulation of thermal convection. In a closed large-volume reactor, diamond films with good crystallinity were obtained on (111)Si substrates; the narrowest full width at half-maximum at the Raman shift of 1332.4 cm -1 was 4.9 cm -1 . Lattice images of diamond as well as silicon were simultaneously obtained at the interface of the diamond film using high-resolution transmission electron microscopy (HRTEM). The observed buffer layer 2 nm thick was confirmed in the amorphous layer by nanometer-scale-area electron diffraction with a 2 nm beam probe. Diamond films were preferentially oriented to the [ 1 1 1 ] direction. HRTEM images of the interface were in good agreement with a geometric atomic projection scheme to the (110) plane of the diamond structure; an sp 3 axis of the tetrahedral structure was formed perpendicular to an amorphous buffer layer on the silicon substrate.

Dislocation of epitaxial CVD diamond and the characterization by Raman spectroscopy

Epitaxial diamond thin films were grown on the (100) planes of synthesized type Ib and IIb diamond substrates by the electron-assisted chemical vapor deposition (EACVD) method. The epitaxy was confirmed by reflection high-energy electron diffraction (RHEED) streaky patterns. The etch pits on the surface of the epitaxial thin films on the IIb diamond substrates were identified as edge dislocations by optical microscopy. The etch pit density of dislocation was 4.0 × 104 to 3.3 × 105 cm−2. In the case of absence of luminescence, epitaxial thin films on the IIb diamond substrate were characterized by Raman spectroscopy. In this experiment, Raman spectra are dominated by signal from the substrate rather than from epitaxial thin film at a thickness of 6000A. However, a remarkable relation between dislocation density on epitaxial diamond films and first- and second-order Raman spectra of the IIb diamond substrates was found. When an etch pit density of 4.0 × 104 cm−2 increased by one order of magnitude, the full width at half maximum (FWHM) of a first-order Raman spectrum broadened by 23% from 1.76 to 2.16 cm−1 at a slit width of 0.8 cm−1. The FWHM of a sharp second-order Raman spectrum also broadened from 5.5 to 5.75 cm−1 at a slit width of 2.0 cm−1. These broadenings of first- and second-order Raman spectra were probably caused by the dislocations in the substrate.

Relation between the dislocations in chemically vapour-deposited diamond and the linewidth of the Raman spectrum

Abstract The 13C epitaxial diamond thin films were grown on the (100) planes of synthesized 12C type IIb diamond substrates by electron-assisted chemical vapour deposition. A chemical etching pre-treatment was performed on the substrate to clean the surface. The etchant used consisted of potassium nitrate and potassium chloride. The reactant gas used was a 1% 13C isotope CH4ue5f8H2 mixture gas in order to distinguish between the Raman spectra of the 13C epitaxial film and the 12C diamond substrate. Epitaxial growth of thin films was confirmed by reflection high energy electron diffraction patterns. Etch pits related to dislocations were observed with Nomarski optical microscopy and the use of wet etching. A relation between the etch pit density and the first-order Raman spectrum of the epitaxial CVD diamond was found. When the etch pit density increased from 9.8 × 104 to 4.7 × 105cm−2, the full width at half-maximum of the first-order Raman spectrum broadened from 4.9 to 6.6 cm−1. At the same time, the peak wavenumber of the Raman spectra increased from 1284.3 to 1286.8 cm−1. The slit width was 1.2 cm−1.

Low temperature epitaxial growth of 3C-SiC on (111) silicon substrates

Abstract 3C-SiC single crystals have been grown epitaxially on (111) silicon substrates at relatively low temperature of 850 to 900°C and pressure of 1 Torr. The growth method was similar to electron assisted chemical vapor deposition (EACVD). Reflection high energy electron diffraction patterns showed that a layer of 3C-SiC single crystalline was formed on the Si wafer. Auger electron spectroscopy measurement showed that the layers were stoichiometric.

Epitaxial growth of cubic SiC by hot filament CVD

Abstract Heteroepitaxial films of cubic silicon carbide with twinning have been grown on (111) and (100) Si at 1050°C using hot filament chemical vapor deposition (HFCVD) and a carbonization process. The carbonization process played an important role in formation of the crystalline structure of the grown films. The optimum condition of carbonization on the surface of (100) Si was different from that of (111) Si. The growth rate of the deposited films increased as the substrate temperature was decreased. With both acetylene and propane as a carbon source, epitaxial SiC films were grown at 1050°C on (111) Si.

Crystal growth of epitaxial CVD diamond using 13C isotope and characterization of dislocations by Raman spectroscopy

Abstract 13 C epitaxial diamond films have been grown on 12 C-type IIb diamond substrates doped with boron, using electron assisted chemical vapor deposition. The relation between etch pits due to dislocations in 13 C diamond film and the broadening of the first-order Raman peak was examined. The reactant gas was 13 CH 4 of 99% purity. The substrate temperature was varied from 943 to 1300°C. The uneven surface morphology was confirmed by atomic force microscopy (AFM) and laser microscopy. From 943 to 1030°C, etch pit rows along 〈100〉 were observed. At 991°C, the etch pit density on a row was 3300 to 5000 pits/cm. The Ar + laser beam was focused on a transparent area near the row of etch pits, where the boron impurity of the substrate is less than several 10 ppm. The first-order Raman line of 13 C epitaxial diamond film was broadened to 3.6–4.0 cm −1 . The line broadening was 50–90% compared with that of the 12 C diamond substrate, 2.1–2.4 cm −1 . At 1300°C, there were very few etch pit rows. The broadening was decreased to 23–25%. The slit width was 1.2 cm -1 .

Synthesis and morphology of CVD diamond on Ta and TaC film

Abstract Synthetic diamond films have been deposited on the Si(111) surface, polycrystalline Ta plate, TaC/Si, and TaC/Ta substrates using an electron assisted chemical vapor deposition (EACVD) method. The effects of substrate pretreatment and existence of carbide layer on the diamond nucleation, subsequent growth and morphology have been studied. The substrate pretreatment, scratching by diamond powder, affects nucleation behavior, subsequent growth and morphology of diamond. Existence of carbide layer and formation of carbide on the substrate affects nucleation density, growth rate and morphology of diamond.