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  • 1
    Electronic Resource
    Electronic Resource
    Effect of a microstructure on the formation of self-assembled laser cavities in polycrystalline ZnO (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 1663-1665 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The optical properties of polycrystalline ZnO have been studied to elucidate the occurrence of random laser action. The spatially-resolved refractive index has been mapped out by using the scanning electron energy loss spectroscopy across the grain boundary. It is observed that the refractive index decreases gradually when the probe beam is approaching to the grain boundary. A thin reflective layer of ∼10 nm is found to form in the vicinity of the grain boundary, which assists the optical scattering. The photon scattering factor of the reflective layer has been determined and is shown to correlate well with the results of the coherent backscattering method. Together with the cathodoluminescence studies, it is suggested that the overall structure, which includes the grain and grain boundary, determines the laser action in ZnO. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1374452
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  • 2
    Electronic Resource
    Electronic Resource
    Determination of the optical constants of zinc oxide thin films by spectroscopic ellipsometry (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 72 (1998), S. 3261-3263 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Spectroscopic ellipsometry (SE) has been used to determine the complex pseudo dielectric functions, ε1(E)+iε2(E), of ZnO films on (0001) Al2O3 substrates over the spectral range of 1.33 and 4.96 eV at room temperature. The SE measurements are carried out with E⊥c at angles of incidence of 60° and 65° with respect to the surface normal. Below the band gap, the refractive index n is found to follow the first order Sellmeir dispersion relationship n2(λ)=1+1.881λ2/(λ2−0.05382). A free excitonic structure located at the band edge of 3.32 eV is clearly observed in the pseudo absorption spectrum. Elliott expression with Lorentzian broadening is used to model the pseudo absorption coefficient above the band edge. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.121617
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  • 3
    Electronic Resource
    Electronic Resource
    Dependence of the excitonic transition energies and mosaicity on residual strain in ZnO thin films (2002)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 80 (2002), S. 941-943 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The mosacity and optical properties of ZnO on (0001) Al2O3 grown by pulsed-laser deposition have been studied by x-ray diffraction and spectroscopic ellipsometry. Strong dependence has been found between the grain size and the residual strain along the c axis, εzz, as well as the film texture. In general, strain relieves and texture improves at larger grain size regardless of the growth conditions. The excitonic transition energies are also found to vary in the presence of strain field. It is observed that the transition energies increase with increasing strain and eventually they are resolved into two well-defined bands at the strain of 1.63%. By taking into account of the biaxial strain, the theoretical band structure of ZnO has been considered by solving the Luttinger–Kohn Hamiltonian. Reasonable agreement is found between the theory and experiment. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1448660
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  • 4
    Electronic Resource
    Electronic Resource
    Optical constants of wurtzite ZnS thin films determined by spectroscopic ellipsometry (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 79 (2001), S. 3612-3614 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The complex dielectric functions of wurtzite ZnS thin films grown on (0001) Al2O3 have been determined by using spectroscopic ellipsometry over the spectral range of 1.33–4.7 eV. Below the band gap, the refractive index n is found to follow the first-order Sellmeir dispersion relationship n2(λ)=1+2.22λ2/(λ2−0.0382). Strong and well-defined free excitonic features located above the band edge are clearly observed at room temperature. The intrinsic optical parameters of wurtzite ZnS such as band gaps and excitonic binding energies have been determined by fitting the absorption spectrum using a modified Elliott expression together with Lorentizan broadening. Both parameters are found to be larger than their zinc blende counterparts. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1419229
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  • 5
    Electronic Resource
    Electronic Resource
    Electronic structures of polycrystalline ZnO thin films probed by electron energy loss spectroscopy (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 77 (2000), S. 1484-1486 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The microstructure of polycrystalline ZnO thin films grown on amorphous fused quartz has been studied by transmission electron microscopy and electron energy loss spectroscopy (EELS). The optical functions of the grain and grain boundary of ZnO acquired from EELS are compared to elucidate the mechanism of the formation of self-assemble laser cavities within this material. It is found that the refractive index of the grain boundary is significantly lower than that of the grain due to the lack of excitonic resonance. This large refractive index difference between the grain and grain boundary substantiates the scenario that the formation of laser cavities is caused by the strong optical scattering facilitated in a highly disordered crystalline structure. In addition, our results also imply that the optical characteristics of ZnO have very high tolerance on defects. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1290596
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  • 6
    Electronic Resource
    Electronic Resource
    Second harmonic generation in laser ablated zinc oxide thin films (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 572-574 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have observed large second-order nonlinear optical response from zinc oxide (ZnO) thin films deposited on sapphire substrates by pulsed laser ablation. By comparing the second harmonic signal generated in a series of ZnO films with different crystallinity and thickness, we conclude that a significant part of the second harmonic signal is generated at the grain boundaries and interfaces. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.121859
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  • 7
    Electronic Resource
    Electronic Resource
    Ultraviolet lasing in resonators formed by scattering in semiconductor polycrystalline films (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 3656-3658 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A semiconductor laser whose cavities are "self-formed" due to strong optical scattering in highly disordered gain media is demonstrated. The lasers are made of zinc oxide polycrystalline films grown on amorphous fused silica substrates. Lasing occurs at an ultraviolet wavelength of ∼380 nm under optical pumping. Actual images of the microscopic laser cavities formed by multiple scattering have been captured. These results suggest the possibility of using disordered semiconductor microstructures as alternative sources of coherent light emission. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.122853
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  • 8
    Electronic Resource
    Electronic Resource
    Studies of electronic structure of ZnO grain boundary and its proximity by using spatially resolved electron energy loss spectroscopy (2002)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 81 (2002), S. 277-279 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The low electron energy loss and complex dielectric functions of an arbitrary grain boundary and its proximity in ZnO thin films have been studied by using the spatially resolved electron energy loss spectroscopy. The critical point parameters have been determined by fitting the dielectric functions simultaneously with analytical line shape model. Gradual changes have been observed in the dielectric functions spectra. The critical points are found to redshift and then blueshift when the electron beam scanned across the grain boundary, which suggest the distinctive electronic structure not only of the grain boundary but also of the depletion region. In addition, comparison has been made between the experiment and the recent theoretical studies to account for the interband transitions that occur in the grain boundaries. Several features predicted by the theory are qualitatively found to be consistent with our results. The presence of dangling bonds instead of bond distortion is attributed to be the major cause of defects in the grain boundaries of ZnO. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1489721
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  • 9
    Electronic Resource
    Electronic Resource
    Depth profiling of ZnO thin films by cathodoluminescence (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 78 (2001), S. 2667-2669 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The depth-resolved luminescence of the ZnO epilayer has been studied by using cathodoluminescence (CL) at room temperature. Other than the usual excitonic and deep level emissions, two peaks at 3.13 and 2.57 eV have been observed and are attributed to the defects. The variation of all the emission peaks has been examined as a function of accelerating voltage. The decrease of near-band edge emissions with depth is due to the internal absorption caused by the pronounced band tail. The deep level emission, however, is shown to increase with increasing depth. We have modeled the CL spectra with the consideration of internal absorption and determine the profile of the Urbach parameter, EUrbach, to study the structural imperfection at different depths. A strong dependence between the intensity ratios of the defect emissions to the excitonic emission and the imperfection of material has been found. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1368187
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  • 10
    Electronic Resource
    Electronic Resource
    Potassium titanyl phosphate thin films on fused quartz for optical waveguide applications (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 66 (1995), S. 2469-2471 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Thin films of potassium titanyl phosphate (KTiOPO4) for photonic applications have been fabricated on fused quartz substrates by pulsed excimer laser ablation. The textured films were optically uniaxial with the symmetry axis oriented normal to the film surface. The principle component of the second order electric susceptibility was oriented parallel to this symmetry axis and was determined to be about 16 times the magnitude of quartz for the fundamental wavelength of 1.064 μm. This configuration, with the largest nonlinear optical response for polarizations perpendicular to the film surface, is desirable in TM guided wave applications. Planar optical waveguide measurements were performed and the linear waveguide loss was measured. The frequency dependence of χ(2)(ω) was determined and found to be uniform for visible second harmonic wavelengths. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.113998
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