Search

Cd1-xZnxS thin films of variable compositions (x = 0.2, 0.4, 0.6, 0.8) were deposited on glass at room temperature by thermal evaporation process. The prepared samples were annealed at two different temperatures (300 °C, 400 °C) for 1 hour in ambient air. The effects of post-annealing on the structural and optical characteristics were investigated using X-ray diffraction (XRD), spectrophotometry, and Raman spectroscopy (RS) methods. XRD studies suggested that the annealed and as-deposited samples belong to wurtzite structure for all Zn concentrations with a preferential orientation along (002) plane. Spectrophotometry analysis of the samples revealed that the energy band gap decreased with annealing temperature. RS investigated different phonon bands and crystalline phases. Two longitudinal optical phonon modes (1-LO, 2-LO) corresponding to monophase hexagonal structure were observed for all Cd1-xZnxS samples. The observed red-shift and anti-symmetrical nature of the 1-LO phonon mode can be associated with annealing, while the overall blue-shift, except for x < 0.6, was caused by the structural disorders in periodic Cd atomic sub-lattices and broken translational symmetry. The spectroscopic results were strengthened by the XRD studies and their results are consistent. [ABSTRACT FROM AUTHOR]

Thin films of CuZnSe (0 ≤ x ≤ 0.20) have been prepared on glass substrates at room temperature by closed space sublimation. The effect of copper (Cu) concentration on the structural, optical and electrical properties of the prepared films has been investigated using x-ray diffraction (XRD), Raman spectroscopy (RS), spectrophotometery and Hall effect measurements. XRD spectra show that all the films are cubic with (111) preferred orientation. The lattice constants, crystallite size, strain, and dislocation density were calculated from the XRD spectra. The structural analysis shows that crystallite size and crystallinity increase while strain and dislocation density decrease up to 10% Cu addition. However, an opposite trend has been observed beyond 10% Cu concentration. RS was carried out to investigate different phonon bands and crystalline phases. The strong reflection corresponding to the (111) texture in the XRD and the observed longitudinal optical (LO) phonon bands at 251 cm and 497 cm in the Raman spectra reveal the formation of single phase zinc-blende structure. The band gap energy decreases from 2.67 eV to 2.24 eV as the Cu concentration is increased from 0% to 20%. Hall effect measurements shows that electrical resistivity ( ρ) is decreased by about three orders of magnitude from 10.4 × 10 Ω-cm to 47.9 × 10 Ω-cm while, carrier concentration and mobility ( μ) is increased with Cu addition. [ABSTRACT FROM AUTHOR]

Abstract: The present paper reports on a systematic study of the Cu doping effect on the optical, electrical and structural properties of ZnTe:Cu (Cu=0, 6, 8, and 10at%) thin films. Polycrystalline Cu-doped ZnTe thin films were deposited on glass substrates at room temperature by thermal evaporation. A detailed characterization of the Cu-doped ZnTe films were performed by X-ray diffraction (XRD), Spectrophotometry, Fourier transform infrared spectroscopy (FT-IR) and Raman spectroscopy. XRD of the as-deposited Cu-doped ZnTe films belong to single-phase cubic structure of ZnTe with preferential orientation along (111) planes revealed minor effect of Cu content. The interference pattern in optical transmission spectra was analyzed to determine energy band gap, refractive index, extinction coefficient and thickness of the films. Wemple–DiDomenico and Tauc's relation were used for the determination and comparison of optical band gap values. The formation of ZnTe and Cu-doped ZnTe phase was confirmed by FT-IR. AC conductivity in a frequency range of 0–7MHz has been studied for investigation of the carriers hoping dynamics in the films. Raman spectra indicated merely typical longitudinal optical (LO) phonon mode of the cubic structure ZnTe thin film at 194cm−1 because the excitation energy is well above of the optical band-gap of the material and exhibited a blue-shift from 194 to 203cm−1 with Cu which could be associated to the substitution of Zn atom with Cu at the lattice sites. [Copyright &y& Elsevier]

In principal, we described stability of the room temperature ZnSe thin films with thermal annealing deposited onto glass by pulsed laser deposition technique using third harmonic 355nm of Nd: YAG laser beam. Optoelectronic analysis and stability with thermal annealing was described in terms of structural and optical properties. These properties were investigated via X-ray diffraction, atomic force microscope, scanning electron microscope, Raman, Fourier transform infrared and photoluminescence spectroscopies. From the strong reflection corresponding to the (111) plane (2θ=27.48°) and the longitudinal optical “LO” phonon modes at 250cm−1 and 500cm−1 in the X-ray diffraction and Raman spectra, a polycrystalline zincblende structure of the film was established. At 300 and 350°C annealing temperatures, the film crystallites were preferentially oriented with the (111) plane parallel to the substrate and became amorphous at 400°C. Atomic force microscopic images showed that the morphologies of ZnSe films became smooth with root mean squared roughness 9.86nm after annealing at 300 and 350°C while a rougher surface was observed for the amorphous film at 400°C. Fourier transform infrared study illustrated the chemical nature and Zn–Se bonding in the deposited films. For the as-deposited and annealed samples at 300 and 350°C, scanning electron micrographs revealed mono-dispersed indistinguishable ZnSe grains and smooth morphological structure which changed to a cracking and bumpy surface after annealing at 400°C. The physical phenomenon of annealing induced morphological changes could be explained in terms of “structure zone model”. Excitonic emission at 456nm was observed for both as-deposited and annealed film at 350°C. The transmission spectrum shows oscillatory behavior because of the thin film interference and exhibited a high degree of transparency down to a wavelength ~500nm in the IR region. Energy band-gap was increased from 2.65eV to 2.7eV for the annealed crystalline film at 350°C which was further decreased to 2.56eV for the annealed amorphous film at 400°C. The observed results manifested that room temperature pulsed laser ablated ZnSe thin film showed excellent structural, optical and morphological stability up 350°C for optoelectronic applications. [ABSTRACT FROM AUTHOR]

Abstract: The present paper reports on a systematic study of the influence of Zn alloying on the structural and optical properties of Cd1−x Zn x S thin films. X-ray diffraction study for structural analysis reveals that the two binary compounds have been completely transformed into ternary compound with hexagonal (wurtzite) structure with preferred orientation along c-direction with (002) planes. The optical properties such as optical constants and band gap energy of the films were examined by using spectroscopic ellipsometer and Photospectrometery. It was found that the optical constants (n and k) decrease with the addition of Zn content in the alloy. It was also confirmed that the band gap increases with increasing Zn amount in the alloy and is attributed to quantum size effect in the grain size. Raman spectroscopy analysis shows one dominant phonon band at 326cm−1, the so-called longitudinal optical (LO) mode for all the alloy composition (x). The appearance of a single phonon band in the Raman spectra established the formation of single phase hexagonal structured Cd1−x Zn x S thin film. The LO band is asymmetrically broaden and high frequency shifted due to potential fluctuation caused by the dopant material. The AFM results showed that the surface roughness was decreased with increasing Zn content. [Copyright &y& Elsevier]

The structural, vibrational and impedance analysis for (ZnO) 1− x (Sb 2 O 3 ) x composite synthesized by solid state reaction technique were carried out in the present investigation. X-ray diffraction (XRD) study showed that (ZnO) 1− x (Sb 2 O 3 ) x composite has hexagonal (wurtzite) crystal structure. Variation in lattice constants with Sb-doping indicated the proper incorporation of Sb dopant in ZnO host matrix. The results of Raman spectroscopy test suggested the signature of E 2 (high) and E 1 (TO) Raman modes, and verified the wurtzite structure of (ZnO) 1− x (Sb 2 O 3 ) x composite. Two additional phonon bands (671, 712) cm −1 appeared in Raman spectra of composite samples due to the existence of the lattice defects caused by Sb doping or may be other intrinsic lattice defects formed during the synthesis of (ZnO) 1− x (Sb 2 O 3 ) x composite. The frequency dependent on the electrical characteristics, such as, impedance ( Z ), dielectric constant ( ε ) and AC conductivity ( σ ) have been studied in a range of frequencies for different Sb concentration at room temperature. The electrical measurement results showed that the impedance increased with Sb dopant concentration, while dielectric constant and AC conductivity decreased with Sb dopant concentration. [ABSTRACT FROM AUTHOR]