Infrared dielectric functions and phonon modes of high-quality ZnO films

Abstract

Infrared dielectric function spectra and phonon modes of high-quality, single crystalline, and highly resistive wurtzite ZnO films were obtained from infrared (300–1200 cm−1) spectroscopic ellipsometry and Raman scattering studies. The ZnO films were deposited by pulsed-laser deposition on c-plane sapphire substrates and investigated by high-resolution x-ray diffraction, high-resolution transmission electron microscopy, and Rutherford backscattering experiments. The crystal structure, phonon modes, and dielectric functions are compared to those obtained from a single-crystal ZnO bulk sample. The film ZnO phonon mode frequencies are highly consistent with those of the bulk material. A small redshift of the longitudinal optical phonon mode frequencies of the ZnO films with respect to the bulk material is observed. This is tentatively assigned to the existence of vacancy point defects within the films. Accurate long-wavelength dielectric constant limits of ZnO are obtained from the infrared ellipsometry analysis and compared with previously measured near-band-gap index-of-refraction data using the Lyddane–Sachs–Teller relation. The ZnO model dielectric function spectra will become useful for future infrared ellipsometry analysis of free-carrier parameters in complex ZnO-based heterostructures.

Three-Photon Absorption in Zno Film Using Ultra Short Pulse Laser

“…In wurtzite ZnO crystals, The non-polar phonon modes with symmetry E 2 have two frequencies, E 2 (high) is associated with oxygen atoms and E 2 (low) is associated with Zn sublattice. The described phonon modes have been reported in the Raman scattering spectra of bulk ZnO [22,23]. In Figure 11, we present a typical non-resonant Raman scattering spectrum from ZnO nanocrystal obtain under the 633 nm non-resonant excitation on of He-Ne laser.…”

Structural, optical and ferroelectric properties of V doped ZnO

“…The polar modes exhibit different wave numbers for the transverse optical (TO) and longitudinal optical (LO) phonons. The non-polar phonon modes E 2 split as E 2 (high), associated with oxygen atoms and E 2 (low), associated with Zn sub lattice (Ashkenov et al 2003;Damen et al 1966). Figure 3 shows the Raman spectra for all the samples in the range of 100-1,000 cm -1 .…”

Inner surface enhanced femtosecond second harmonic generation in thin ZnO crystal tubes

“…Both the XRD and Raman data show that the sample has an excellent wurtzite crystalline structure. 17 Figure 2 shows representative SHG emission ͑solid line͒ of the thin ZnO crystal rod under excitation by femtosecond laser with wavelength of 774 nm and power of 700 mW at room temperature. For comparison, a thick ZnO single crystal solid rod ͑diameter ϳ3 mm͒ was measured under the same excitation conditions and its emission spectrum ͑dashed line͒ was also shown.…”

“…X-ray diffraction, confocal micro-Raman and low-temperature photoluminescence measurements consistently indicate high quality of the samples. 17,18 For the SHG measurements, wavelength tunable femtosecond laser beam with a ϳ0.1 mm focus waist was focused onto the surface of the rods. The femtosecond pulse was generated from a selfmode-locked Ti:sapphire oscillator ͑Tsunami͒ pumped by a 10 W solid-state laser ͑Millennia͒.…”