Tianfu Ma

Full color light emission from amorphous SiCx:H with organic–inorganic structures

Hydrogenated amorphous silicon carbide films with an organic–inorganic compound structure were fabricated by using organic carbon source xylene (C8H10), in a traditional radio frequency plasma-enhanced chemical vapor deposition system. Strong full-color light emission ranging from 630 to 420 nm was observed at room temperature. The results of photoluminescence and photoluminescence excitation experiments showed the emission was originated from the radiative recombination at band tails of the inorganic SiC matrix. Moreover, luminescence from the transition between discrete energy levels, which were associated with organic π-conjugated carbon systems, was also observed at resonant excitation conditions.

Red–green–blue light emission from hydrogenated amorphous silicon carbide films prepared by using organic compound xylene as carbon source

We fabricated hydrogenated amorphous silicon carbide (a-Si1-XCX:H) films by the plasma-enhanced chemical vapor deposition technique using organic compound xylene (C8H10) as the carbon source, which was initially attempted by W. A. Nevin H. Yamagishi, M. Yamaguchi, and Y. Tawada, Nature 368, 529 (1994). Here we used different preparation conditions from those authors to produce xylene-based a-Si1-XCX:H films, and a different light emission behavior of the films has been observed at room temperature. The light emission wavelength can be shifted from 630 nm to 450 nm by changing the optical band gap (Eopt) of the films from 2.3 eV to 3.5 eV, nearly covering the whole visible light range, which was never reported previously. Fourier transform infrared spectra showed that the configuration of the material was a combination of organic aromatic rings and inorganic SiC networks.

The influence of the growth conditions on the structural and optical properties of hydrogenated amorphous silicon carbide thin films

Two series of hydrogenated amorphous silicon carbide (a-SiC:H) films have been prepared by using plasma-enhanced chemical-vapor deposition (PECVD) with the gas mixture of methane (CH4) and silane (SiH4). The influence of the r.f. power density on the structural and optical properties of the films has been investigated with the CH4 gas ratio in the total gas flow rate ranging from 50 to 90%. The r.f. power density is an important parameter which affects both the carbon content and the structures of the films. Under high r.f. power condition, the samples are Si-rich and the structure of them is described as a disordered amorphous silicon network in which hydrogen atoms are incorporated in the form of Si–CH2 and Si–CH3 entities and carbon atoms are in a sp3 carbon-related configuration. The optical band gaps of these samples increase with the increase of the gas flow ratio. Under low r.f. power condition, the samples are carbon-rich and the structure of them is a mixed phase of amorphous Si and graphite-like C clusters. The optical band gap of the series samples decrease with the increase of the gas flow ratio.

Novel luminescence properties of a-C:H films produced by using an organic source at various substrate temperatures

Abstract Hydrogenated amorphous carbon films have been fabricated using an organic carbon source (xylene), at substrate temperatures 10–300°C in plasma-enhanced chemical vapor deposition (PECVD) system. We found that, the carbon films contain π-bonded clusters with aromatic units, whose size decreased with increasing substrate temperature. For samples deposited at lower substrate temperature, several photoluminescence (PL) bands were observed, which we attributed to the recombination through some luminescent centers associated with π-bonded structures. For samples deposited at higher substrate temperature, only a single peak with a width greater than the widths of the PL peaks observed in the lower temperature films, which is similar with that of methane-based a-C:H films.

Novel photoluminescence from hydrogenated amorphous carbon films prepared by using xylene source

Hydrogenated amorphous carbon thin films were prepared by using organic hydrocarbon source, xylene (C 8 H 10 ), in a plasma enhanced chemical vapor deposition-(PECVD) system. In contrast to a single broad PL peak from methane (CH 4 )-based hydrogenated amorphous carbon films, a new PL feature was observed from xylene-based a–C:H films in the blue-green light region. It was found that the aromatic-structures were enhanced in xylene-based a–C:H films deposited at high radio frequency power, which may result in the existence of luminescence centers in the carbon films and induce the appearance of a new PL peak.

The improvement on blue light emission from hydrogenated amorphous silicon carbide films prepared from an organic source

A series of hydrogenated amorphous silicon carbide (a-Sil−xCx:H) films (0<x≤1) was grown by using an organic source, xylene (C8H10), instead of methane (CH4) in a conventional plasma enhanced chemical vapor deposition system. The optical band gap of these samples was altered over a wide range by changing the gas ratio of C8H10 to SiH4; the maximum ratio was 3.5 eV. Photoluminescence (PL) measurements were carried out at room temperature by using a Xe lamp as an excitation light for samples deposited at different conditions. Contrary to earlier reports, we found that the PL peak is blueshifted with increasing optical band gap and the PL intensity increased.

Visible electroluminescence from amorphous hydrogenated silicon carbide prepared by using organic carbon source

A series of amorphous silicon carbide (a-SiC:H) films were prepared by using an organic carbon source, xylene, in a plasma chemical vapor deposition system. Visible electroluminescence (EL) was observed from the device structures of Al/a-Si:H/a-SiC:H/ITO/glass at room temperature. The EL peak was changed from 2.0 to 2.3 eV with increasing carbon content in a-SiC:H films and the EL devices have open voltages at approximately 2.5 V. The EL behavior was investigated and the influence of the EL device structure was also discussed in the paper.

FULL-COLOR PHOTO- AND ELECTRO-LUMINESCENCE FROM HYDROGENATED AMORPHOUS SILICON CARBIDE FILMS PREPARED BY USING ORGANIC SOURCE

A series of hydrogenated amorphous silicon carbide (a-Si1-xCx:H) films (0 < x ≤ 1) were grown by using an organic source, xylene (C8H10), instead of methane (CH4) in a conventional plasma enhanced chemical vapor deposition system. The optical band gap of these samples was altered over a wide range by changing the gas ratio of C8H10 to SiH4, the maximum value can be reached as high as 3.6eV. Photoluminescence (PL) measurements were carried out at room temperature by using a Xe lamp as an excitation light. It was found that the PL peak is blue shifted with increasing optical band gap. The xylene-based a-SiC:H electro-luminescence (EL) device structure was also fabricated and room temperature EL behavior was investigated. It was found that the EL peak depended on the band gap of a-C:H films and a stable emission can be obtained by using the suitable structure parameters.

Structure and Photoluminescence of Hydrogenated Amorphous Carbon Films Produced by Using Aromatic Hydrocarbon Source

The organic carbon source –xylene(C 6 H 6 -C 2 H 4 ), was used to fabricate a-C:H films in plasma enhanced chemical vapor deposition system. The structures and bonding configurations were characterized and compared with that of conventional methane-based samples by using Fourier Transform Infrared spectroscopy and Raman scattering technique. Strong room temperature luminescence in blue-green light range was found and the PL feature was quite different from that of methane-based a-C:H films.

Optical and electrical properties of a-Si1-xCx:H and uc-Si1-xCx:H films prepared by using methane and xylene source

Hydrogenated amorphous silicon carbide (a-Si1-xCx:H) films were fabricated in the plasma-enhanced chemical vapor deposition system by using silane (SiH4) and two kind of carbon sources, methane (CH4) and xylene (C8H10), respectively. The optical band gap of methane-made a-Si1- xCx:H was varied from 1.9 eV to 2.6 eV while that of xylene-made a-Si1-xCx:H could be extended to 3.5 eV. Fourier transform infrared spectra demonstrated the existence of aromatic ring in xylene-made a-Si1-xCx:H, which is much different from the carbon configuration of methane-made a-Si1-xCx:H. Visible light emission at room temperature was observed from xylene-made a-Si1-xCx:H films. The photoluminescence peak shifted from 630 nm (1.97 eV) to 450 nm (2.75 eV) when the optical band gap of samples increased from 2.3 eV to 3.5 eV. KrF pulse laser with wavelength of 248 nm was used to crystallize these two kinds of films at room temperature. For both samples the conductivities can reach 10-5S/cm and are enhanced by over four orders of magnitude.