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Author: search.filters.author.Chen, WKSubject: search.filters.subject.photoluminescence

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Now showing 1 - 7 of 7
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    Photoluminescence studies of GaN films of different buffer layer and doping concentration
    (1998-02-01)
    Shen, CC
    ;
    Shu, CK
    ;
    Lin, HC
    ;
    Ou, J
    ;
    Chen, WK
    Photoluminescence (PL) measurements of GaN films with various buffer thicknesses and Si-doping concentrations have been carried out. PL response of one specific sample was studied for temperature dependence. The results showed that the band gap energy reduction is linearly proportional to the temperature increase with a slope of similar to-4 x 10(-4) eV.K-1 and that the activation energies for donor-bound and acceptor-bound exciton transitions are 15 and 18 meV, respectively. In Si-doped GaN films, the PL data indicated that the reduced gap depends on the third power of carrier concentration as n(1/3). We also obtained a concentration coefficient of 2.34 x 10(-4) eV.cm and a band gap energy of 3.426 eV in the undoped GaN film.
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    Item type:Item,
    Photoluminescence studies of GaN films of different buffer layer and doping concentration
    (1998-02-01)
    Shen, CC
    ;
    Shu, CK
    ;
    Lin, HC
    ;
    Ou, J
    ;
    Chen, WK
    Photoluminescence (PL) measurements of GaN films with various buffer thicknesses and Si-doping concentrations have been carried out. PL response of one specific sample was studied for temperature dependence. The results showed that the band gap energy reduction is linearly proportional to the temperature increase with a slope of similar to-4 x 10(-4) eV.K-1 and that the activation energies for donor-bound and acceptor-bound exciton transitions are 15 and 18 meV, respectively. In Si-doped GaN films, the PL data indicated that the reduced gap depends on the third power of carrier concentration as n(1/3). We also obtained a concentration coefficient of 2.34 x 10(-4) eV.cm and a band gap energy of 3.426 eV in the undoped GaN film.
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    Growth temperature reduction for isoelectronic As-doped GaN
    (2003-03-01)
    Lee, WH
    ;
    Huang, HY
    ;
    Chen, WC
    ;
    Lee, CF
    ;
    Chen, WK
    As-doped GaN films were grown at different temperatures by atmospheric metalorganic chemical vapor deposition. A higher electron Hall mobility, narrower line width in photoluminescence, and longer spatial correlation length of the filmes were obtainable at low growth temperatures compared to undoped GaN grown at the same temperatures as a result of isoelectronic As-doping.
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    Optical properties of Zn1-xCdxSe epilayers grown on (100)GaAs by molecular beam epitaxy
    (2004-08-01)
    Kuo, MC
    ;
    Chiu, KC
    ;
    Shih, TH
    ;
    Lai, YJ
    ;
    Yang, CS
    Zn1-xCdxSe epilayers were grown on (100) GaAs substrates by molecular beam epitaxy. Lattice constants of the epilayers were measured by (004) rocking curve X-ray diffraction. A full width at half maximum of 475 to 2100 arcsec was obtained. The dependence of the energy gap on temperature, measured by the photoluminescence (PL) spectra, was fitted by Varshni's [Y. P. Varshni: Physica 34 149 (1967)] and O'Donnell's [R. P. O'Donnell and X. Chen: Appl. Phys. Lett. 58 2924 (1991)] models. The fitting parameters beta (161 K to 368K) and (hv) (13 meV to 24 meV), related to phonon energy, were obtained from Varshni and O'Donnell fits, respectively. The activation energies calculated from the integrated PL intensity versus inverse temperature decrease as the Cd content increases. The broadening of the PL linewidth with temperature was fitted by Gamma(T) = Gamma(0) + Gamma(a)T + Gamma(LOI)/[exp(homega(LOI)/kT) - 1] + Gamma(LO2)/[exp(homega(LO2)/kT) - 1] + Gamma(i)exp(-/kT). The impurity binding energy, (E-b), was found to decrease as the Cd composition increases.
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    The electronic structure and optical properties of phosphorus implanted GaN films
    (2000)
    Shu, CK
    ;
    Lee, WH
    ;
    Huang, HY
    ;
    Chuang, CH
    ;
    Chen, WK
    We have studied optical and electronicc transition properties of GaN layers grown by MOCVD which are implanted by isoelectronic impurities of phosphorus (P). The P-implanted samples were treated by rapid thermal annealing to recover implantation-induced damages. A strong emission band around 430 nm were observed in P-implanted sample due to the recombination of bound exciton to P-hole isoelectronic traps. From the Arrhenius plot, the hole binding energy about 180 meV localized at the P-isoelectronic trap and the exciton localization energy of 28 meV were obtained. According to first-principle total-energy calculations, we suggest that the implantation likely induces N-I or P-related defects. From the PLE, we found that the absorption by band-to-band and shallow donors dominates the yellow luminescence (YL) and the implantation of P has induced localized states that not only increase the YL but also suppress the transition from the free electron-hole pairs to the deep-levels.
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    Metastable photoluminescence in heavily Mg-doped GaN grown by metalorganic chemical vapor phase epitaxy
    (2000)
    Shu, CK
    ;
    Lee, WH
    ;
    Pan, YC
    ;
    Huang, HY
    ;
    Chen, HH
    The long-term transient spectra of heavily Mg-doped GaN have been investigated. As the excitation power density increased, the broad Mg-induced emission band showed blue-shift revealing characteristic of donor-acceptor pair (DAP) recombination. We also observed an unusually slow intensity decay. The characteristic time constants range from several tenths to a few hundred seconds for emission between 360 and 460 nm. Our results are interpreted in terms of metastability due to compounded effects of differential DAP population and recombination rates and uneven acceptor distribution.
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    Crystalline structure changes in GaN films grown at different temperatures
    (1997-05-15)
    Lin, HC
    ;
    Ou, J
    ;
    Chen, WK
    ;
    Chen, WH
    ;
    Lee, MC
    Thin GaN films were grown on (0001) sapphire at various temperatures between 520 and 1050 degrees C using metalorganic chemical vapor deposition (MOCVD). Optical properties and crystalline structures of the films were investigated by means of photoluminescence, Raman scattering, and X-ray diffraction. A noticeable structure transition occurred at around 750 degrees C with higher growth temperatures favoring the hexagonal structure and lower ones the cubic. Defect formation was also seen to be temperature dependent. The yellow luminescence which was clearly observed in our 700-850 degrees C films was attributable to the cubic and hexagonal structure mixing. The drastic reduction of yellow luminescence and the substantial enhancement of near band edge emission in the 950-1050 degrees C films indicated that this temperature range is optimum for growing high quality wurtzite films.