Takeshi Imura

Formation of SiH bonds on the surface of microcrystalline silicon covered with SiOx by HF treatment

Abstract Infrared absorption due to the surface chemical bonds on microcrystalline silicon (μ c -Si) was investigated with recycling procedures of thermal oxygenation accompanied with dehydrogenation and HF etching. Siue5f8H bonds were reformed on the surface of μ c -Si by HF etching of oxygenated μ c -Si. The mechanism of the Siue5f8H bond formation was proposed. It was suggested that formation of =SiH 2 , SiH 2 x or -SiH 3 group depended on the kind of a crystalline plane.

Boron Doping of Hydrogenated Silicon Thin Films

Doping of boron into Si:H thin films by means of glow-discharge decomposition of SiH4 and B2H6 pre-mixed gas has been studied. Optical and electrical properties of these B-dopen Si:H films have been measured, and crucially discussed in relation to the contents of bonded H and incorporated B atoms in the specimens. A new deposition condition has been presented for obtaining the p-type film which has a wide optical gap amounting to 1.79 eV and dark conductivity exceeding 10-1 Ω-1cm-1.

Transformation of microcrystalline state of hydrogenated silicon to amorphous one due to presence of more electronegative impurities

Abstract When a slight fraction (∼ 2 mol %) of N 2 is added into H 2 , sputtering atmosphere for microcrystalline hydrogenated Si films, without changing other fabrication parameters, the amorphous film rather than microcrystalline one forms. The stabilization mechanism of the amorphous film of Si is discussed through TEM and IR observations of this kind of transformation from microcrystal to amorphous state.

PHOTOPRODUCTION OF IONS FROM CHLOROPHYLL α IN SOLUTION STUDIED BY FLASH PHOTOLYSIS and PHOTOCONDUCTIVITY

Abstract— Ionic species were detected electrically on flash excitation of chlorophyll α following rapid production of the triplet state of the pigment. The action spectrum of photocurrent agreed well with the absorption bands of the pigment in the visible region; the threshold for the formation of ionic species in acetonitrile was 1.8 eV. Oxygen gas introduced into the solution completely prevented the appearance of the triplet and ionic species. The latter are suggested to result from electron‐transfer between the triplet pigments. Decay processes of the ionic species varied markedly with changes in the solvent polarity. Direct photo‐ionization of the pigment could be observed by UV excitation in some non‐polar solvents.

Diffusion of indium and tin into a-SiC:H from transparent electrode studied by XPS

Abstract The influence of the degradation of transparent electrode on the solar cell performance is interpreted from the comparison between depth distributions of impurities and Fermi-level shift by means of surface analyses. The reduction of Inue5f8Sn oxide followed by diffusing into p-layer as In lifts Fermi=level upward competing with B acceptor, which eventually leads the depression of open circuit voltage.

Fabrication of Si:H Alloy with Plenty of –SiH3 by Reactive Sputtering onto Low Temperature Substrate

Si:H alloy with strong infrared absorption bands due to the –SiH3 group was fabricated by means of a planar magnetron r.f. sputtering technique in hydrogen gas onto a low temperature substrate. The content of the –SiH3 group increases greatly by cooling down the single crystal silicon wafer substrate to about -60°C. The deposition rate was 1200 A/min. The deposit Si:H alloy is composed of microcrystalline grains with a uniform polyhedron or spherical shape and a uniform diameter of 100 A.

Energy Levels and Charge Carrier Generation in Crystalline Chlorophyll-a Studied by Photoconduction and Fluorescence

Photoconduction and fluorescence were studied in solid state chlorophyll-a(Chl-a) films which were composed of microcrystals of Chl-a-water adduct. The transient photocurrent, rising without time delay for an exciting flash, decayed with a second order reaction. Two types of response were distinguished in the action spectrum of photocurrent on continuous illumination: One of them corresponded to the absorption of Chl-a molecular crystal, and the other, appearing longer wavelength (820 nm, 1.51 eV), was ascribed to the direct transition to a conduction band below the first excited singlet state. The thermal band gap of 1.48±0.02 eV was obtained from the activation energy for dark conductivity. The fluorescence of crystalline Chi-a was observed at 794 nm.

New methods for determining the three-dimensional distribution of hydrogen in amorphous SiH

Abstract In addition to the electron excited Auger spectra of Si (LMM), keV Ar+ ion bombardment of Siue5f8H produces new peak at 86 eV. A correlation appears to exist between the intensity of this new peak and H content. Ion-induced Auger electron spectroscopy has been proposed for the study of homogeneity of H in amorphous Siue5f8H. Quantitative analyses of H in amorphous Siue5f8H deposited by glow discharge in SiH4 and reactive sputtering have been carried out by Rutherford backscattering spectrometry, which can detect at least 5 at.% H atoms in Siue5f8H through the change of stopping power.

Ion-induced Auger electron spectroscopy—A new detection method for compositional homogeneities of alloyed atoms in silicon

Abstract Auger spectra of Si LMM transitions induced by keV Ar+ ion bombardment of Si alloy systems have been studied. The spectra observed are composed of two well-defined peaks termed elsewhere the “atomic-like” and “bulk-like” peaks, respectively. A clear correlation has been found between the intensity of the atomic-like peak lying at 88 eV and the content of the foreign atoms alloyed with Si. Experiments were carried out on metallic silicides, or Si alloys with Au, Cu, Pd and Ni, and covalently bonded non-metallic Si alloys of C and H. From these studies, we propose that ion-induced Auger electron spectroscopy might be a useful tool for the determination of alloyed foreign atoms as well as for the study of their compositional homogeneity in binary alloy systems of silicon.