Fang Rong-Chuan

Optical absorption and photoluminescence of unhydrogenated amorphous carbon films

Abstract Unhydrogenated amorphous carbon (a-C) films were prepared by a laser beam technique. Optical absorption, photoluminescence (PL) and the dependence of PL spectra on the incident laser intensity were studied. The optical gap, peak energy of the PL spectrum and band tail width change with preparation bias voltage. At room temperature PL spectra exhibit a superlinear behaviour at lower incident intensity, linear behaviour at higher intensities, and a large blue shift of peak energy with increasing excitation intensity. These results can be qualitatively explained in the light of the distribution of gap states and tail state population.

Growth of ZnO Thin Films on Lattice-Matched Substrates by Pulsed-Laser Deposition

ZnO films were grown on GaN and sapphire substrates by pulse laser deposition, respectively. The effects of crystalline quality on the optical properties in ZnO epitaxial layers were investigated by x-ray rocking curve and photoluminescence. The x-ray rocking curve of the film deposited on the GaN substrate has the full width half maximum (FWHM) of 0.45 degrees, whereas the FWHM of the x-ray θ-rocking curve of the ZnO film deposited on a sapphire substrate was measured to be about 0.77 degrees. In photoluminescence (PL) measurement, the intensity of UV photoluminescence for the ZnO film on the GaN substrate decreased by approximately two orders of magnitude in comparison with that of the ZnO film on sapphire. It is concluded that the UV luminescence intensity almost does not depend on the textured growth of the ZnO thin film.

Infrared spectra of a-Si:H, Cl films

Abstract Films of amorphous silicon (a-Si:H,Cl) containing about 10 atomic % hydrogen and 2–8 at % chlorine have been prepared using the r.f. glow-discharge technique with a mixture of H 2 and SiCl 4 . The infrared spectra showed in addition to the hydrogen induced absorption bands at 2100, 2000, 840, 890 and 860 cm −1 the following new absorption lines: 545 cm −1 due to SiCl stretching, 787 and 737 cm −1 which might be caused by the Si-HCl bending vibrations. The absolute chlorine content was measured using sulphocyanic mercury spectrophotometric and chlorine ion selective electrode methods.

Thermal Conductivity of Diamond-Based Silicon-on-Insulator Structures

Diamond films of various thickness (1-300 μm) were deposited on single-crystal Si active (300 μm) by a microwave plasma chemical vapor deposition method using gaseous mixtures of methane and hydrogen. After thinning of the Si layer by machine and ion-beam polishing a diamond-based silicon-on-insulator structure with final Si layer thickness of about 1 μm is formed. Thermal conductivity of this structure material with various thicknesses of diamond and Si layer was measured. Compared with bulk silicon, the thermal conductivity of the silicon-on-diamond structure with 300 μm diamond and 1 μm silicon increases by 850%.

Deposition of Diamond Film on Aluminum Nitride Ceramics and the Study of Their Thermal Conductance

Diamond films (DF) have been deposited on AlN ceramic substrates by hot filament chemical vapour deposition method. The diamond nucleation on AlN ceramics has been investigated. A nucleation density more than 108 cm-2 was obtained on this kind of insulating polycrystalline substrate under common deposition conditions. The thermal conductance of the DF/AlN compound materials has been studied by photothermal deflection technique. The thermal diffusivity of the DF/AlN is higher than that of the AlN ceramics, and will increase as the diamond films grow thicker.

Temperature Dependence of Photoluminescence in Porous Silicon

Porous silicon samples have been successfully prepared by electrochemical etching technique, which show intense photoluminescence (PL) in the visible wavelength region. The measurements of the temperature dependence of PL in porous silicon show that the wavelength of the luminescent peak shifts to the blue and the PL band width does not change as the temperature of the sample increases over a wide range. The intensities of PL are measured as a function of temperature showing the confined exciton recombination behaviour, and the activation energies of 68.6 and 205 meV of the excitons have been obtained for the low temperature and high temperature regions, respectively. The results suggest that the PL in porous silicon is due to the radiative recombination in a quantum wire system.

Raman spectrum of Ba-Y-Cu-O system

Abstract The Raman spectra of a set of samples with nominal composition Ba x Y 1−x CuO 3 (0.005 ⩽ x ⩽ 0.8) which are synthesized under the same condition have been measured. It is observed that the main characters of Raman spectrum are quite different for the two groups of samples with Ba concentration being 0.3 ⩽ x ⩽ 0.8 and 0.005 ⩽ x ⩽ 0.075 respectively. It just coincides with the results two types of phase structures and the difference in superconductivity related to the two ranges of composition. Based on a comprehensive analysis of the results above, the authors suggest that the Raman peak near 605cm -1 likely corresponds to the vibration of CuO 6 octahedra breathing-mode, which play an important role in this system for achieving high transition temperature.

Initial Growth of Thin Films with Low Nucleus Density and Linear Lateral Growth Rate on a Substrate Surface

Based on corrected rate equations, the kinetics is revealed for the initial growth of thin films with a low nucleus density and a linear lateral growth rate on a substrate surface. In this case, the mobility and coalescence terms in the rate equations are neglected, and the coverage term takes a dominant role. All the calculated results are in agreement with experimental data. These results introduce a new scaling in the case of dominant coverage, which is different from the those in the case of coalescence or mobility in a dominant role.

Effect of Growth Temperature on the Band Lineup of Ge/CdTe(111) Polar Interfaces

By using synchrotron radiation photoelectron spectroscopy, the band lineup of Ge/CdTe(111) interfaces grown at different temperatures have been measured. Experimental studies show that the valence band offset of Ge/CdTe(111) interface grown at room temperature is 0.88?0.1 eV, which agrees well with previously reported value. While as for the interface grown at 280?C, an obvious reduction of valence band offsets is observed and attributed to the effect of different interface dipole.

VALENCE BAND OFFSET AND INTERFACE FORMATION OF GE/ZNSE(100) STUDIED BY SYNCHROTRON RADIATION PHOTOEMISSION

Abstract The formation and band lineup of the Ge/ZnSe(100) interface have been studied by synchrotron radiation photoemission spectroscopy. Core level intensity measurements from the ZnSe substrate as well as from the Ge overlayer show a two-dimensional deposition of Ge film. Core level spectra indicate that Ge atoms react with Se atoms slightly at the interface. We derive a valence band offset of 1.76±0.1eV for Ge/ZnSe(100).