Y. Kurata

Optical properties of Si clusters and Si nanocrystallites in high-temperature annealed SiOx films

Structure, optical absorption and photoluminescence (PL) properties of SiOx films subjected to thermal annealing at 750–1100 °C are investigated. Si crystallites with a few nanometers in size are observed in the SiO1.3 and SiO1.65 films annealed at 1100 °C. Threshold energies in optical absorption of the Si nanocrystallites are higher than that for bulk Si, suggesting a contribution from quantum confinement effects. The PL spectrum shows a remarkable increase in intensity after annealing at temperatures above 1000 °C. This PL behavior is closely related to the formation of Si nanocrystallites by the annealing. The PL peak energy of the annealed films shifts to higher energy with decreasing crystallite size but does not follow the blueshift for the absorption threshold energy. These results suggest that a localized state contributes to the PL mechanism. The SiO1.8 film annealed at 1100 °C, which contains no Si crystallites, exhibits an intense PL similar to the annealed SiO1.3 and SiO1.65 films. It is impl...

Vibrational properties of SiO and SiH in amorphous SiOx:H films (0 ≤ x ≤ 2.0) prepared by plasma-enhanced chemical vapor deposition

The stretching and bending absorptions arising from SiO and SiH bonds in amorphous SiOx:H films, prepared by rf glow discharge decomposition of a SiH4O2 mixture at 300°C, have been investigated by infrared absorption measurements as a function of the O content, x. Changes in the profiles of the SiH stretching absorption as a function of x were examined on the basis of a random-bonding model. A charge-transfer model is employed to derive the oscillator strength of the SiH stretching absorption and the peak frequencies of the SiH and SiO stretching absorption, for the Si(Si4−nOn)(n = 1−4) and HSi(Si3−nOn)(n = 0−3) bonding configurations. The absorption over the range 500–900 cm−1, related to the SiH and SiO bending motions, can be decomposed into five components around 650, 780, 800, 840 and 880 cm−1. It is found that the intensities of the 780, 840 and 880 cm−1 bands are closely correlated with those of the SiH stretching absorptions at 2115, 2200 and 2260 cm−1, respectively. The origins of these absorption bands along with the 650 and 800 cm−1 bands are discussed.

Photoluminescence of Hydrogenated Amorphous Carbon Films

Hydrogenated amorphous carbon films have been prepared by the glow-discharge decomposition of ethylene gas. The film shows wide properties depending on gas temperature during discharge. With increasing gas temperature from 200 to 350°C, hydrogen content in the film decreases, and thereby the optical gap decreases from 2.6 to 1.2 eV and the ESR spin density increases from ~1017 to ~1019 cm-3. The photoluminescence spectrum consists of two emission bands. The peak energy of the main band shifts from 1.93 to 1.64 eV as the gas temperature increases. Emission intensity is very insensitive to measurement temperature.

Optical properties of silicon nanocrystallites in polycrystalline silicon films prepared at low temperature by plasma-enhanced chemical vapor deposition

Abstract Silicon crystallites produced by low-temperature plasma-enhanced chemical vapor deposition technique have been shown to have size-dependent photoluminescent and second harmonic generation responses. The crystalline volume fraction was estimated by Raman spectra and the grain sizes of crystallites were measured by X-ray diffraction. The structural chemical properties of poly-Si films were studied by means of Fourier-transform infrared spectroscopy and transmission spectrophotometry. The size- and shape-dependent second-harmonic generation (SHG) of poly-Si films is also studied. The resonant SHG spectra show the fine structure with peak position at approximately 3.26 eV which is attributed to the response from Si–SiO 2 interface (for aged films). The second resonant peak can be explained as the size-dependent SHG response from the bulk of nanocrystallites.

Bonding configuration and defects in amorphous SiNx:H films

Amorphous SiNx:H films were prepared by rf glow discharge of SiH4‐NH3 mixtures at 300 °C, and the optical properties and the density Ns of Si dangling bonds obtained from electron spin resonance were investigated as a function of the N content x. The slope E0 in the Urbach form of the absorption coefficient and Ns, respectively, have a maximum at x=1.2 and 0.7. The dependence of E0 on x was examined on the basis of the random‐bonding model including H atoms, and the dependence of Ns was connected with the optical gap and E0, according to the weak‐bond dangling‐bond conversion model.

Structure and grain boundary defects of recrystallized silicon films prepared from amorphus silicon deposited using disilane

The structure of polycrystalline Si (poly‐Si) films, prepared by annealing amorphous Si (a‐Si) films deposited using Si2H6, has been investigated by x‐ray diffraction (XRD), Raman scattering, transmission electron microscopy (TEM), and electron spin resonance, as functions of deposition conditions, such as deposition temperature Td (450–580 °C) of the a‐Si and annealing time under a fixed temperature of 600 °C. A dominant texture of the poly‐Si films changed from a 〈100〉 texture for Td below 530 °C to a 〈111〉 for Td above 530 °C, independent of the deposition rate of the a‐Si films and of the film thickness. Although the XRD grain size was independent of Td, the TEM grain size increased from 1.0 to 2.5 μm with decreasing Td. It is suggested that the increase in this TEM size is caused by enhanced lateral growth of 〈100〉 grains due to the presence of strain. The spin density Ns and the factor g were found to first increase with the annealing time, and rapidly decreased after the films were crystallized. It...

Amorphous SiN:H dielectrics with low density of defects

Amorphous SiNx:H films were prepared by rf glow discharge (GD) of SiH4‐N2‐H2 mixtures at 300 °C using a new decomposition technique. The optical gap Eg increases slowly with the ratio N2/SiH4 up to a critical gap Egc of 2.5–3.0 eV, and then rapidly increases up to 5.3 eV. The spin density Ns from electron spin resonance of Si dangling bonds increases with N2/SiH4 until Eg reaches Egc. Above Egc, Ns rapidly decreases in contrast with that of conventional GD films, but in similarity to pyrolytic films. The slope B in Tauc equation for optical absorption corresponds well with Ns.

ESR and electrical properties of P-doped microcrystalline Si

Abstract The dependences on phosphorus doping of ESR, conductivity, X-ray diffraction and hydrogen vibrational spectra have been investigated for microcrystalline Si films prepared by a new glow-discharge decomposition method where the substrate is placed in a heated plasma gas. The results are compared with those for amorphous Si : H and polycrystalline Si films. A higher deposition rate of 80–160 A min−1 and larger crystallite sizes of 150–250 A have been found than in other methods of preparation. The morphology of an amorphous phase in the microcrystalline film is different from that in an amorphous Si : H film, and the width of the conduction band tail-states in the amorphous phase portion is considerably narrower. A large conductivity in the P-doped microcrystalline films is interpreted as arising from an enhanced upward shift of the Fermi level permitted by the reduction in the tail-state width. A strong correlation between the conductivity and hydrogen bonded in SiH2 groups was found, the conducti...

Bonding properties of glow‐discharge polycrystalline and amorphous Si‐C films studied by x‐ray diffraction and x‐ray photoelectron spectroscopy

Polycrystalline and amorphous Si‐C films were prepared by rf glow‐discharge decomposition of silane‐methane mixtures at 700 °C. We have demonstrated that polycrystalline SiC films with large grains grow under heavy hydrogen dilution. The bonding properties as a function of film composition and hydrogen dilution were characterized by means of x‐ray diffraction and x‐ray photoelectron spectroscopy. Crystallization takes place at around C content x=0.5 in Si1−xCx, accompanying some segregation of carbon atoms in grain boundaries, as a result of a preference for heteronuclear bonds. It was shown that C‐C(C3−nSin) (n=0–3) bonds appear in the carbidic phase of C‐rich films, leading to occurrence of compressive strain in the crystalline SiC grains. In addition, effects of hydrogen dilution were discussed in correlation with the strain.

EFFECTS OF DEPOSITION TEMPERATURE ON POLYCRYSTALLINE SILICON FILMS USING PLASMA-ENHANCED CHEMICAL VAPOR DEPOSITION

The 200-nm-thick polycrystalline Si films were deposited by changing the deposition temperature (Td=150–750 °C) using plasma-enhanced chemical vapor deposition of monosilane–hydrogen mixtures. The structural and bonding properties were examined using techniques of Raman scattering, x-ray diffraction, infrared (IR) absorption, and electron spin resonance. Except for Td at 150 and 650 °C, crystallization of the films was observed, and the occurrence of two IR absorption bands around 850 and 1000 cm−1 and an increase in the density of Si dangling bonds were observed in the range of Td higher than 500 °C. These origins were discussed in connection with the mechanisms of disappearance of crystalline phases from the film at Td=650 °C.