Surface characterization and microstructure of ITO thin films at different annealing temperatures

In this study, the electron beam evaporation method is used to generate an indium tin oxide (ITO) thin film on a glass substrate at room temperature. The surface characteristics of this ITO thin film are then investigated by means of an AFM (atomic force microscopy) method. The influence of postgrowth thermal annealing on the microstructure and surface morphology of ITO thin films are also examined. The results demonstrate that the film annealed at higher annealing temperature (300 °C) has higher surface roughness, which is due to the aggregation of the native grains into larger clusters upon annealing. The fractal analysis reveals that the value of fractal dimension D_f falls within the range 2.16-2.20 depending upon the annealing temperatures and is calculated by the height-height correlation function.     

Super-resolution readout property of bismuth-doped antimony-based thin film as a functional mask for read-only memory

Bismuth-doped antimony-based (Sb_100?x Bi _x , x=2.46) thin films were presented as a functional mask for super-resolution readout of read-only memory (ROM). The pit size of the ROM was 390?nm, and super-resolution readout was realized on a dynamic tester with laser wavelength of 780?nm and the numerical aperture of the focusing objective lens of 0.45. The carrier-to-noise ratio (CNR) of 22?dB, readout threshold power of 0.8?mW and super-resolution readout cycles of 2×10⁴ was achieved. The influence of film thickness and readout power on CNR was investigated. The reflectivity and transmittance of the film with different temperature at wavelength of 780?nm were detected, and the super-resolution mechanism of the bismuth-doped antimony-based thin films as the functional mask layer was discussed.     

Structure,optical spectroscopy and dispersion parameters of ZnGa2Se4 thin films at different annealing temperatures

Thin films of ZnGa₂Se₄ were deposited by thermal evaporation method of pre-synthesized ingot material onto highly cleaned microscopic glass substrates. The chemical composition of the investigated compound thin film form was determined by means of energy-dispersive X-ray spectroscopy. X-ray diffraction XRD analysis revealed that the powder compound is polycrystalline and the as-deposited and the annealed films at T_a = 623 and 673 K have amorphous phase, while that annealed at T_a = 700 K is polycrystalline with a single phase of a defective chalcopyrite structure similar to that of the synthesized material. The unit-cell lattice parameters were determined and compared with the reported data. Also, the crystallite size L, the dislocation density δ and the main internal strain ε were calculated. Analyses of the AFM images confirm the nanostructure of the prepared annealed film at 700 K. The refractive index n and the film thickness d were determined from optical transmittance data using Swanepoel's method. It was found that the refractive index dispersion data obeys the single oscillator model from which the dispersion parameters were determined. The electric susceptibility of free carriers and the carrier concentration to the effective mass ratio were determined according to the model of Spitzer and Fan. The analysis of the optical absorption revealed both the indirect and direct energy gaps. The indirect optical gaps are presented in the amorphous films (as-deposited, annealed at 623 and 673 K), while the direct energy gap characterized the polycrystalline film at 700 K. Graphical representations of ε₁, ε₂, tan δ, ? Im[1/ε*] and ? Im[(1/ε* + 1)] are also presented. ZnGa₂Se₄ is a good candidate for optoelectronic and solar cell devices.     

Optical characterization of bromo-alkoxyl-substituted copper phthalocyanine derivative thin films

A series of thin films of copper phthalocyanine derivatives with bromine and alkoxyl substituents [CuPc(OC₈H₁₇)₄Br_m, m=0,1,2,4] were prepared on single-crystal silicon substrates by spin coating. The ellipsometric spectra of the films have been studied on a rotating analyzer–polarizer type of scanning ellipsometer. The optical, dielectric constants and absorption coefficients of the films in 500–800 nm wavelength region were obtained. The results show that the complex refractive index, dielectric constants and absorption coefficient of these thin films are influenced regularly by bromine substituent on conjugated macrocycle. It was found that there are approximately linear relationships between the resonance absorption wavelengths of the films and the average number of bromine atoms substituted on the phthalocyanine ring.     

Study on optical anisotropy properties of SiO2 films with different thermal annealing temperatures

SiO2 films are deposited on Si substrates by an ion beam sputtering technique and continuously annealed in a quartz culture dish in air at various annealing temperature ranging from 20 to 750 ℃ with a step of 100 ℃ for a fixed time of 24 h. The effects of thermal treatment on optical anisotropy properties of SiO2 films are investigated by spectroscopic ellipsometry. When the annealing temperature is 550℃, the optical anisotropy properties of SiO2 film is minimum. The obtained results indicate that the optical anisotropy properties of SiO2 films can be improved by a proper thermal annealing process.     

Optical gate realization with thin CdS films

A spray deposited thin (6 m) CdS film laser induced optical device (LIOD) was studied experimentally and theoretically. The all optical bistable (all-OB) and the hybrid bistable (HB) features at 210 K were investigated. It is shown for the first time that the observation of equal contrasted all-OB and HB loops is possible in thin CdS films. The slope of the all-OB loops were calculated with a new theoretical model which is established on the thermal enhanced shift of the absorption edge and the transmitted light equilibrium condition. A good agreement with the experiments is found. Furthermore, it is pointed out that the electron life time determines the fashion and the contrast of the HB loops. In this context the proof is furnished that the maximal possible HB loops is observed. Finally, the influence of Joule's heat on OB and HB is demonstrated.     

Optical characterization of thin thermal oxide films on copper by ellipsometry

A complete optical characterization in the visible region of thin copper oxide films has been performed by ellipsometry. Copper oxide films of various thicknesses were grown on thick copper films by low temperature thermal oxidation at 125 °C in air for different time intervals. The thickness and optical constants of the copper oxide films were determined in the visible region by ellipsometric measurements. It was found that a linear time law is valid for the oxide growth in air at 125 °C. The spectral behaviour of the optical constants and the value of the band gap in the oxide films determined by ellipsometry in this study are in agreement with the behaviour of those of Cu₂O, which have been obtained elsewhere through reflectance and transmittance methods. The band gap of copper oxide, determined from the spectral behaviour of the absorption coefficient was about 2 eV, which is the generally accepted value for Cu₂O. It was therefore concluded that the oxide composition of the surface film grown on copper is in the form of Cu₂O (cuprous oxide). It was also shown that the reflectance spectra of the copper oxide–copper structures exhibit behaviour expected from a single layer antireflection coating of Cu₂O on Cu. Received: 19 July 2001 / Accepted: 27 July 2001 / Published online: 17 October 2001     

Optical and X-ray characterization of ferroelectric strontium-bismuth-tantalate (SBT) thin films

Metal-organic chemical vapor deposition (MOCVD) made layers of strontium-bismuth-tantalate (SBT) were characterized by spectroscopic ellipsometry (SE) using the Adachi model [S. Adachi, Phys. Rev. B 35 (1987) 7454-7463]. The evaluated optical parameters were correlated with the physical and chemical behavior examined by X-ray diffraction (XRD).As a result, it was possible to fit the measured spectra with the Adachi model in a wide range covering the region of the band gap. The Adachi model provides electronic layer parameters like the transition energy E₀ and broadening Γ. Our investigations established a correlation between XRD-determined average grain size and the electronic layer parameters.     

Optical constants of thin germanium films

The paper gives the values of the optical constants of thin films of germanium obtained by evaporating germanium in a vacuum onto glass slides in the region of 0·35–0·78 for an index of absorptionk and 0·35–2·5 for refractive indexn. The results are compared with the values obtained by other authors and with the values ofn andk for single crystals. It is shown that these values for thin films and single crystals slightly differ quantitatively but agree fairly well qualitatively, which had not been sufficiently the case in previous papers.

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, , 0,35 0,78 k 0,35–2,5 n. n, k . , , , , .

     

Optical properties of Ge-As-Te thin films

Different compositions of Ge_xAs₁₀Te_90−x (x=5, 10, 15, 20, and 25 at%) chalcogenide glasses were prepared by the usual melt quench technique. Amorphous Ge_xAs₁₀Te_90−x thin films were deposited onto cleaned glass substrates using the thermal evaporation method. Transmission spectra, T(λ), of the films at normal incidence were measured in the wavelength range 400-2500 nm. A straightforward analysis proposed by Swanepoel based on the use of the maxima and minima of the interference fringes has been used to drive the film thickness, d, the complex index of refraction, n, and the extinction coefficient, k. It was found that, the addition of Ge content at the expense of Te atoms shifts the optical band gap to the short wavelength side (blue shift of the optical band gap) while the refractive index are found to decreases. The obtained results of the refractive index were discussed in terms of the electronic polarizability and the single-oscillator Wemple and DiDomenico model (WDD). The optical absorption is due to the allowed non-direct optical transitions. The observed increase in the optical band gap with the increase in Ge content was discussed in terms of the width of the tail states in the gap and the covalent bond approach.     

Optical properties and structures of silver thin films deposited by magnetron sputtering with different thicknesses

A series of thin Ag films with different thicknesses grown under identical conditions are analyzed by means of spectrophotometer. From these measurements the values of refractive index and extinction coefficient are calculated. The films are deposited onto BK7 glass substrates by direct current (DC) magnetron sputtering. It is found that the optical properties of the Ag films can be affected by films thickness.Below critical thickness of 17 nm, which is the thickness at which Ag films form continuous films, the optical properties and constants vary significantly with thickness increasing and then tend to a stable value up to about 40 nm. At the same time, X-ray diffraction measurement is carried out to examine the microstructure evolution of Ag films as a function of films thickness. The relation between optical properties and microstructure is discussed.     

Optoelectronic characterization of Au/Ni/n-AlGaN photodiodes after annealing at different temperatures

The optoelectronic characteristics of Ni/Au Schottky photodiodes based on Al_0.35Ga_0.65N were investigated. The transmission of the Ni (50 Å)/Au (50 Å) layer was determined by evaporating it on a quartz substrate. As evaporated, the transmission coefficient in the 200–350 nm wavelength range was found to be 43 to 48%. Annealing at temperatures of up to 400 °C did not influence the transmission coefficient. After annealing at 500 °C, the transmission coefficient increased from 50 to 68% over the 200–350 nm range. The reverse bias current was optimised in terms of annealing temperature and was found to be as low as 1.94×10⁻¹³ A after annealing at 400 °C for a 0.6 mm diameter contact. The Schottky barrier heights increased with annealing temperature reaching as high as 1.46 and 1.89 eV for I–V and C–V measurements, respectively. The quantum efficiency was measured to be 20.5% and the responsivity reached its peak of 0.046 A/W at 275 nm. The cut-off wavelength was 292 nm.     

Optical bistability in thin molecular films

Within the framework of a developed model of a medium consisting of molecular J aggregates and placed in an external resonant light field, it is shown how exciton self-localization and the dependence of the dipole moment components on molecule deformation affect optical bistability. Deformation of the molecules substantially facilitates the observation of a bistable dependence of the state of the medium and of the transmitted field amplitude on the incident field amplitude. The evolution of the system to a quasi-stationary, nonground state after the passage of an electromagnetic field pulse under the conditions of self-localization of excitons is studied.     

Optical characterization of PLD grown nitrogen-doped TiO2 thin films

Nitrogen-doped TiO₂ thin films were prepared by pulsed laser deposition (PLD) by ablating metallic Ti target with pulses of 248 nm wavelength in reactive atmospheres of O₂/N₂ gas mixtures. The layers were characterized by UV-VIS spectrophotometry and variable angle spectroscopic ellipsometry with complementary profilometry for measuring the thickness of the films. Band gap and extinction coefficient values are presented for films deposited at different substrate temperatures and for varied N₂ content of the gas mixture. The shown tendencies are correlated to nitrogen incorporation into the TiO_2-xN_x layers. It is shown that layers of significantly increased visible extinction coefficient with band gap energy as low as 2.89 eV can be obtained. A method is also presented how the spectroscopic ellipsometric data should be evaluated in order to result reliable band gap values.     

Optical properties of stannous oxide thin films

Thin films of stannous oxide (SnO) have been prepared by the electron-beam evaporation method. Film properties, such as refractive indexn, extinction indexk, and absorption coefficient, were studied in the wavelength range between 200 nm and 2 000 nm with different methods. The surface roughness of SnO thin films has been found to depend linearly on the film thickness in the range 400 <d < 2 000 nm. The optical transition in SnO thin films shows direct transition corresponding to an optical gap of 2.85 eV.     

Optical properties of nanostructured InSe thin films

Thin films of InSe were prepared by thermal evaporation technique. The as-deposited films have nano-scale crystalline nature and the annealing enhanced the degree of crystallinity. The optical properties of nanocrystalline thin films of InSe were studied using spectrophotometric measurements of transmittance, T, and reflectance, R, at normal incidence of light in the wavelength range 200–2500 nm. The optical constants (refractive index, n, and absorption index, k) were calculated using a computer program based on Murmann's exact equations. The calculated optical constants are independent of the film thickness. The optical dispersion parameters have been analysed by single oscillator model. The type of transition in InSe films is indirect allowed with a value of energy gap equals to 1.10 eV, which increased to 1.23 eV upon annealing.     

Optical response of thin plasma-polymer films with non-spherical silver nanoparticles

The size and shape of silver nanoparticles which are embedded in a plasma-polymer matrix were obtained by transmission electron microscopy and analyzed with optical image processing. We used a sample in which silver particles were present before and after reshaping caused by thermal annealing in adjacent regions. As most of the particles appeared as elongated rotational ellipsoids, the major and minor half axis were determined for each particle. We adopted the model of Gans in the Rayleigh approximation to calculate for each investigated particle the extinction spectra from to using the data from the image processing. The various spectra for 368 silver particles were added to get total extinction spectra for the sample as deposited and after reshaping, respectively. We found good agreement with the experimental spectra. The blue shift of the plasma-resonance absorption, which occurs due to the reshaping of the silver particles during thermal annealing, was also confirmed by using only changes in the particle sizes and shapes. Received: 23 July 1997 / Revised: 27 October 1997 / Accepted: 3 December 1997