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Abstract: Raman scattering and polarization-dependent synchrotron radiation X-ray absorption, in combination, have been employed to examine the residual stress of undoped GaN epitaxial layers grown on Si by molecular beam epitaxy and Si-doped n-type GaN layers grown on sapphire by metalorganic chemical vapor deposition. Values of the lattice constant of different GaN films can be deduced from the interatomic distances in the second coordination shell around Ga by polarization-dependent extended X-ray absorption fine structure analysis and the strain of the films can be obtained. This result is further confirmed by Raman scattering spectra in which the phonon modes show a significant shift between different GaN epitaxial layers with different growth conditions. [Copyright &y& Elsevier]

Abstract: Two sets of (Al x Ga1−x )0.5In0.5P films were grown on lattice-matched GaAs by low pressure metalorganic chemical vapor deposition under different conditions and studied by Nomarski microscopy (NM), atomic force microscopy (AFM), photoluminescence (PL) and Raman scattering. NM and AFM images show cross-hatch patterns, related to dislocations and lattice mismatch, from one set of samples, but none from another set of films. Comparative PL and Raman measurements and analyses indicated the correlation between surface and optical properties. The degree of variations in compositions and film quality with the growth conditions was found from the spectral analyses. Raman spectral features are more sensitive to the sample growth parameter variations. The line shape analysis of line width, integrated intensity ratio and spatial correlation model fitting leads to information about the order of the sample crystalline quality. The optimum growth conditions have been obtained from our comprehensive analyses. [Copyright &y& Elsevier]

Abstract: The wavelength shifts in the photoluminescence (PL) from low indium composition (∼ 3%) InGaN epitaxial thin films, grown on sapphire substrates by metalorganic chemical vapour deposition, has been studied by a combination of experiment and theory. As temperature increases from 6 K, the PL peak energy red-shifts very slightly first, then blue-shifts to reach a maximum at near 100 K, and red-shifts again till room temperature. This unique PL behaviour, indicating the existence of the phase separation, is interpreted qualitatively from the spatial variation of band structure due to the In-compositional fluctuation. Theoretical calculation, based upon a model involving the band-tail states in the radiative recombination, explains the experimental data successfully. [Copyright &y& Elsevier]

Examines the Raman spectra of lead titanate thin films grown by metalorganic chemical vapor deposition. Use of single-crystal KTaO[sub 3] and fused quartz as substrates; Overview of soft-mode theory; Shift in optical mode frequencies for the thin films and substrates.

Abstract: Al x In y Ga1−x−y N quaternary alloys with different ratios of Al/In were grown by metal-organic chemical vapor deposition on GaN/Al2O3 substrates. The structural and emission properties of the as-grown samples were investigated, respectively, by high-resolution X-ray diffraction and photoluminescence (PL) measurements. The PL emission character is related to the two prominent quenching bands, which have been determined to be located at around 1.1eV and 1.7eV above the valence band, respectively, by the method of optical quenching of photoconductivity. PL emission is most intense when the Al/In ratio is 7.5 for the Al x In y Ga1−x−y N layer. In addition, a stronger quenching phenomenon with Al/In ratio of 5.0 in Al x In y Ga1−x−y N is observed in accordance with a reduction of the intensity of Al x In y Ga1−x−y N-related emission peak. [Copyright &y& Elsevier]

Abstract: A series of GaN thin films were grown on Si substrate under different conditions using metalorganic chemical vapor deposition (MOCVD) and characterized by Nomarski microscopy (NM), optical reflectance (OR), high-resolution X-ray diffraction (HRXRD), Raman scattering (RS) and photoluminescence (PL). NM showed different patterns for GaN/Si grown under different growth and source flow parameters. XRD, RS and PL measurements confirmed their wurtzite crystalline GaN structures, and the corresponding line shape analyses revealed their difference corresponding to the NM observations. The control and improvement of the crystalline cracking in GaN/Si are discussed. [Copyright &y& Elsevier]

Abstract: A new type of large area metal organic chemical vapor deposition (MOCVD) system for the growth of high quality and large size ZnO materials is introduced. Materials properties of the un-doped, n- and p-doped ZnO epi-films grown on sapphire substrates by this MOCVD system are studied by various techniques, including high resolution X-ray diffraction (XRD), UV–Visible optical transmission (OT), photoluminescence (PL) and photoluminescence excitation (PLE), synchrotron radiation X-ray photoelectron spectroscopy (SR-XPS). The wurtzite (w) ZnO crystal structures grown with primary (0002) orientation were identified. Results have shown the high crystalline quality of MOCVD-grown ZnO films, indicated by the narrow XRD, PL and Raman line widths, strong PL signals, sharp OT edge and smooth surface. In particular, high p-type carrier concentration of >1017 cm−3 have been achieved besides the good n-type doping in ZnO. [Copyright &y& Elsevier]