Browsing by Author "DAI, CM"

Now showing 1 - 14 of 14

AN ALTERNATE TREATMENT OF MAGNETIC AND ELECTRIC-FIELD EFFECTS ON THE A-EXCITON SPECTRUM IN CADMIUM-SULFIDE
(1990-01-01)
DAI, CM
;
PEI, JH
;
CHUU, DS
;
電子物理學系
;
電控工程研究所
BINDING-ENERGIES AND EXTERNAL-FIELD EFFECTS OF THE A-EXCITON STATES IN CDS
(1990-03-26)
DAI, CM
;
PEI, JH
;
MEI, WN
;
CHUU, DS
;
電子物理學系
BINDING-ENERGY SPECTRA OF ABC-EXCITONS OF CDS
(1992-09-01)
DAI, CM
;
CHUU, DS
;
電子物理學系
;
Department of Electrophysics
A novel perturbative variational method was employed to calculate the exciton energy spectra of CdS. The band mixing effects were included by taking into account the detail feature of the valence bands. More extensive charcteristics of the energy spectra of A-, B- and C-excitons were identified. It is found that the binding energy of the ground state of a B-exciton is larger than that of an A-exciton, whilst the binding energy of the 2s state of a B-exciton is slightly lower than that of an A-exciton. Our results are compared with the previous theoretical values using the conventional perturbation method and the available experimental data. Better agreements between our results and the observed values are obtained.
COMPOSITION AND CHEMICAL-REACTIONS OF TITANIUM-OXIDE FILMS DEPOSITED BY LASER EVAPORATION
(1991-03-15)
DAI, CM
;
SU, CS
;
CHUU, DS
;
電子物理學系
;
光電工程學系
Thin films were deposited on Pyrex glass substrates from Ti and TiO2 targets at room temperature by laser evaporation technique. These films were characterized by scanning electron microscopy, Auger electron spectroscopy, and depth profile analysis. The films deposited from Ti target are TiC(x) and TiO(y) matrix, while films from TiO2 target are almost stoichiometric in oxygen. The films have a smooth surface morphology under a laser power density of 5 X 10(6) W/cm2, which is close to the critical intensity for evaporation. The interface reaction of these films is strong, and the Ti atoms diffuse into the substrate.
GROWTH OF HIGHLY ORIENTED TIN OXIDE THIN-FILMS BY LASER EVAPORATION DEPOSITION
(1990-10-29)
DAI, CM
;
SU, CS
;
CHUU, DS
;
電子物理學系
;
光電工程學系
HIGH ORIENTATION CDS THIN-FILMS GROWN BY PULSED LASER AND THERMAL EVAPORATION
(1992-05-01)
DAI, CM
;
HORNG, L
;
HSIEH, WF
;
SHIH, YT
;
TSAI, CT
Undoped CdS films have been grown by pulsed laser evaporation (PLE) and thermal evaporation (TE) techniques on Corning's 7059 glass at a substrate temperature between room temperature and 250-degrees-C. The deposition rates are 0.07 angstrom/s for PLE and 60 angstrom/s for the TE technique. These as-deposited films have high (002) preferred orientation by both techniques even without preheating the substrate. However, films deposited by PLE have more preferred orientation and larger grain size. These features make the PLE films have sharper Raman peaks, smaller Raman shift of surface mode and more overtones of longitudinal optical phonon mode observed than those in TE films. The transparency of PLE or TE films for wavelengths which are larger than that of absorption edge is around 90% on average.
OBSERVATION OF THE TRANSVERSE OPTICAL PHONON MODE IN CDS FILM AT 4880-A EXCITATION
(1992-03-15)
DAI, CM
;
CHUU, DS
;
電子物理學系
;
Department of Electrophysics
The transverse-optical (TO) phonon mode in a CdS film with a thickness less than 410 angstrom is observed at 4880 angstrom excitation wavelength which is above the band gap of CdS bulk (2.42 eV) at room temperature. This phenomenon is ascribed to the size quantization of the free carrier in the low-dimensional thin-film structure. The quantum size effect causes a blue shift of the band gap in the as-deposited CdS thin film. The Raman shift of the TO mode of CdS film is around 220 cm-1. The softening energy of the TO phonon mode is about 8 cm-1. It was found that this softening energy is independent of the film thickness.
QUANTUM SIZE EFFECTS IN CDS THIN-FILMS
(1992-05-15)
CHUU, DS
;
DAI, CM
;
電子物理學系
;
Department of Electrophysics
Resonant Raman spectroscopy is used to study quantum size effects in CdS films. The lattice softening of the CdS LO-phonon mode in a CdS film with a thickness less than 800 angstrom is observed. As the thickness is less than 410 angstrom, the TO-phonon mode is observed at 4880 angstrom excitation wavelength, which is above the band gap of bulk CdS (2.42 eV) at room temperature. These phenomena are attributed to the size quantization effects of the grain size and the low-dimensional thin-film structure. The quantum size effects cause a blueshift of the band gap in the as-deposited CdS thin film. The peak of the TO-phonon-mode Raman line of the CdS film is observed around 220 cm-1, which has a shift of 8 cm-1 from the Raman line of the most active TO-phonon mode of bulk CdS. The magnitude of softening energy of the TO-phonon mode is observed to be independent of the film thickness.
RAMAN INTENSITY ENHANCEMENT OF THE SI PEAK BY CDS THIN-FILMS
(1991-12-16)
DAI, CM
;
CHUU, DS
;
HSIEH, WF
;
交大名義發表
;
電子物理學系
A method, which utilizes interference enhanced Raman scattering and resonant Raman scattering techniques, is used to overcome the low efficiency of Raman methods to diagnose highly reflective materials. As applied to the p-type Si wafer, the enhanced gain is up to nearly a factor of 80 at 4880 angstrom excitation. Because of the strong absorption of the scattered light, it is recommended that the suitable deposited thickness of CdS films should not be thicker than 700 angstrom.
RAMAN INVESTIGATIONS OF THE SURFACE-MODES OF THE CRYSTALLITES IN CDS THIN-FILMS GROWN BY PULSED LASER AND THERMAL EVAPORATION
(1991-06-15)
CHUU, DS
;
DAI, CM
;
HSIEH, WF
;
TSAI, CT
;
電子物理學系
CdS films have been grown on Corning glass by pulsed laser evaporation (PLE) and thermal evaporation (TE) techniques at a substrate temperature between room temperature and 250-degrees-C. The quality of these films is investigated by resonance Raman scattering, x-ray diffraction and optical transmittance. Our results reveal that the Raman shifts of the surface phonon mode are observed with 300 and 297 cm-1 by PLE and TE techniques, respectively, and as many as four overtones are obtained by PLE method. The difference of Raman shift between these two techniques are caused by the discrepancy of crystallite sizes which is larger for PLE technique. The crystallite sizes are in the range of 200-500 angstrom in diameter. Highly oriented films have been grown by both of the techniques even when the substrate is at room temperature.
SHALLOW DONOR IMPURITY STATES OF A SEMICONDUCTOR IN A UNIFORM MAGNETIC-FIELD
(1991-07-01)
DAI, CM
;
CHUU, DS
;
電子物理學系
;
光電工程學系
;
Department of Electrophysics
The perturbative-variational method is used to study the hydrogen-like shallow donor impurity states of the isotropic semiconductor under a uniform magnetic field from a spherical symmetry approach. Using a magnetic field dependent parameter, which is added in the simple hydrogenic wave functions, the eigenvalues can be determined by optimizing the parameter. The results we obtained are in good agreement with the previous works up to gamma = 5 (e.g., 10(6) T for atoms) for the ground state. The extension to the transitional region by this method is considerably higher than other approaches.
SHALLOW SURFACE DONOR IMPURITY STATES OF GE, SI AND GAP
(1990-10-01)
PEI, JH
;
DAI, CM
;
CHUU, DS
;
電子物理學系
;
電控工程研究所
SHALLOW SURFACE IMPURITY STATES OF ISOTROPIC AND ANISOTROPIC SEMICONDUCTORS
(1989-11-01)
PEI, JH
;
DAI, CM
;
CHUU, DS
;
電控工程研究所
;
光電工程學系
THE VIBRATIONAL-MODE SOFTENING IN THIN-FILM CDS
(1992-02-01)
DAI, CM
;
CHUU, DS
;
電子物理學系
;
Department of Electrophysics
Lattice softening of the CdS LO phonon mode was observed by resonant Raman spectroscopy (RRS). This phenomenon was interpreted in terms of the combined effects of grain size and low-dimensionality of the film. As the thickness of the film decreases below 800 angstrom, the influence of the free-surface on the vibrational spectrum becomes more prominent. Higher order harmonics of the LO-mode also are observed. The intensity of the Raman line is enhanced as it approaches the maximum of the fluorescence emission peak.