Yongping Guo

Deposition of high quality cubic boron nitride films on nickel substrates

The well‐crystallized cubic boron nitride (c‐BN) films have been prepared on polycrystalline Ni substrates using a hot filament assisted rf plasma chemical vapor deposition method. X‐ray diffraction showed that high quality c‐BN films had been deposited without hexagonal BN (h‐BN) or amorphous BN codeposition. Both (111) and (100) faces were observed in scanning electron microscopy images. These results suggested that Ni had catalyst effects on the nucleation and the growth of c‐BN phase and inhibited the formation of h‐BN.

TEXTURED GROWTH OF CUBIC BORON NITRIDE FILM ON NICKEL SUBSTRATES

Textured cubic boron nitride (c‐BN) films have been deposited on (220) oriented crystallized polycrystalline nickel substrate by a hot filament assisted rf plasma chemical vapor deposition method. X‐ray diffraction shows that the films are (220) preferentially grown, the peak ratio of (220) to the main peak [i.e., the (111) peak] is about 5.2. The scanning electron microscopy images exhibit regular grain shapes. Most of the grains are rectangular, also indicating the (220) growth. The grain size is about 5 μm. The well‐matched Ni lattice with c‐BN, the catalytic effect of Ni, and the appropriate rf bias are considered to be the key factors in the textured growth.

High-photosensitivity a-SiGe: H films prepared by RF glow discharge plasma CVD method

Abstract Highly photosensitive and narrow band gap a-SiGe: H films have been prepared by the RF glow discharge plasma CVD method. The photosensitivity was 2.01 × 10 5 for the film with an optical band gap of E g = 1.47 eV. H 2 dilution and a relatively high RF power are attributed to the improving of the optoelectrical properties. Thermally induced changes of the a-SiGe:H films have been also investigated.

Ohmic contacts on diamond by B ion implantation and Ta-Au metallization

Ohmic contacts on diamond have been achieved by B ion implantation and subsequent metallization with a Ta/Au bilayer. The pre-treatment of p-diamond film using boiling aqua regia was effective in reducing oxygen, which plays an important role in forming the Au/Ta/p-diamond ohmic contacts. Sputter deposition and implantation accelerate the interfacial reaction between Ta and diamond film. The formation of TaC makes our contacts to be ohmic in the as-deposited state. Upon annealing, the quantity of TaC increases and it makes the ohmic behavior be improved.

Modulation of Three Dimensional Photonic Band Gap in Visible Region

Three dimensional (3D) SiO2 photonic crystals films were fabricated on quartz substrate by vertical deposition method. The effects of various preparation parameters on optical properties were studied by optical transmission measurements. Bragg reflection on parallel sets of (111) planes were observed in all the samples. The center wavelength of [111] photonic band gap (PBG) varied from 450 nm to 680 nm with the increasing sphere size. For a given sphere size, the (111) Bragg reflection of as-deposited sample shifted towards lower wavelengths as the sintering temperature T increased. The role of evaporation temperature on the optical properties of the film was also investigated. The PBG can be correspondingly modulated in visible region by changing various preparation parameters.

INTERFACE PROPERTIES OF A-SI-H/A-SICX-H SUPERLATTICE

Abstract Measurements of IR spectra and low energy absorption, using the constant photocurrent method, have been carried out for a-Si:H/a-SiC x :H superlattices fabricated by an r.f. plasma deposition technique. It has been found that there exist high concentrations of Si H bonds and high concentration of Si C bonds at a-Si:H-a-SiC x :H interfaces. The interfacial hydrogen shows a lower thermal stability than that of the hydrogen in the bulk materials. A possible microscopic mechanism of interfacial defects in the a-Si:H/a-SiC x :H superlattices is discussed.

The Effect of RF Power on the Growth of c-BN Films on Nickel Substrates

High quality cubic boron nitride (c-BN) films have been prepared on polycrystalline Ni substrates by hot filament assisted rf plasma chemical vapor deposition (CVD). Grazing incidence X-ray diffraction (XRD) measurements, X-ray photoelectron spectroscopy (XPS), and infrared absorption spectroscopy reveal that the resulting films are composed of the c-BN phase. The well-faceted c-BN grains are viewed in scanning electron microscopy (SEM) images. Based on results of XRD measurements, we investigate the effect of rf power on the phase purity of the films and the orientation of the grains. It is found that rf power is a determining parameter in improving the growth of c-BN grains and suppressing the formation of h-BN phase. An appreciable rf power can result in a preferentially (200) and (220) oriented growth of c-BN films. The optimum power density of rf plasma is at the intermediate level of approximately 2.83 W/cm 2 . The momentum model of the reaction radicals is applied to discuss the effect of the rf power on the growth of c-BN films on Ni substrates.

ELECTRICAL PROPERTIES OF Si1-X-YGeXCY FILMS GROWN BY ION IMPLANTATION AND SOLID PHASE EPITAXY

Si0.875-yGe0.125Cy ternary alloy films were grown on Si by ion implantation of C into Si0.875Ge0.125 layers and subsequent solid phase epitaxy. It was shown that C atoms were nearly incorporated into substitutional sites and no SiC was formed in the SiGeC films by optimal two-step annealing. There is a prominent effect of C contents on carrier transport properties. Compared with strained Si0.875Ge0.125 film, enhanced Hall mobility has been obtained in partially and fully strain compensated Si0.875-yGe0.125Cy layer due to the reduction of lattice strain.

Room-temperature visible photoluminescence from C clusters embedded in thin SiO2 films

The composite films of c and SiO2 were fabricated by an rf co-sputtering technique and post-annealing treatment, strong PL spectra with a peak energy about 2.22 eV was obtained at room temperature. We investigated the PL spectra dependence on substrate temperature annealing temperature, and sample thickness. Using Raman scattering, IR transmission and XRD measurements, we studied the structures of the composite films. Some results were discussed.

Creation process of thermally induced defects in boron-doped hydrogenated amorphous silicon-carbon films

Abstract The creation process of thermally induced defects in B-doped hydrogenated amorphous Six.C1-x samples has been studied by measuring the annealing time dependence of dark d.c. conductivity. The results show that the creation process of thermally induced defects exhibits a stRevched-exponential-like form; the equilibrium values increase with increasing annealing temperature while the relaxation time decreases with increasing annealing temperature. In particular, the stRevched-exponential factor also decreases with increasing annealing temperature, which is contrary to that of the annealing process of frozen-in defects. A model involving two different trapping processes of transportable H in the defect creation and annealing processes is proposed to explain this result.