Significance of Al on the morphological and optical properties of Ti1−xAlxN thin films

TiN and Ti_1−xAl_xN thin films with different aluminum concentrations (x = 0.35, 0.40, 0.55, 0.64 and 0.81) were synthesized by reactive magnetron co-sputtering technique. The structure, surface morphology and optical properties were examined using Grazing Incidence X-ray Diffraction (GIXRD), Atomic Force Microscopy (AFM), Raman spectroscopy and spectroscopic ellipsometry, respectively. The structure of the films were found to be of rocksalt type (NaCl) for x = 0.0–0.64 and X-ray amorphous for x = 0.81. AFM topographies show continuous mound like structure for the films of x between 0.0 and 0.64, whereas the film with x = 0.81 showed smooth surface with fine grains. Micro-Raman spectroscopic studies indicate structural phase separation of AlN from TiAlN matrix for x > 0.40. Ti_1−xAl_xN has the tendency for decomposition with the increase of Al concentration whereas c-TiN and hcp-AlN are stable mostly. The optical studies carried out by spectroscopic ellipsometry measurements showed a change from metallic to insulating behavior with the increase in x. These films are found to be an insulator beyond x = 0.81.     

Initial study on the structure and optical properties of Zn1−xFexO films

Zn_1−xFe_xO (x = 0, 0.052, 0.103, 0.157 and 0.212) films were prepared by the radio-frequency magnetron sputtering technique on Si (111) substrates and the microstructure of which was characterized by X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscopy. The samples had a preferential c-axis orientation and the position of (002) diffraction peak shifted to the lower degree side with increasing Fe component. In order to investigate the optical transmittance properties of Zn_1−xFe_xO films, we prepared the films on Al₂O₃ (001) substrates simultaneity and the UV-VIS optical transmittance spectra showed that the band gap energy of Zn_1−xFe_xO films decreased with increase of Fe concentration. Photoluminescence spectra of the samples were observed at room temperature.     

The effect of AlN buffer layer on properties of AlxIn1 − xN films on glass substrates

Al_xIn_1 − xN (AlInN) films with x = 0.36 and 0.55 were grown on glass substrate by pulsed direct-current reactive sputtering. X-ray photoelectron spectroscopy depth profiles revealed that oxygen diffused from glass substrate to AlInN films at temperatures ≧ 300 °C. After applying AlN buffer layer, the crystallinity of AlInN films was markedly improved without oxygen contamination observed. The AlN-buffered AlInN films are c-axis-oriented with low full-width-at-half-maximum of 2.9°-3.5°, fine-grained, and low electron concentration, which are comparable with AlInN films grown by other high-temperature processes. AlN buffer layer is proved to be good seeding and diffusion-barrier layers for AlInN films deposited on glass substrates.     

Compositional effects on the optical properties of Gex Sb40−x Se60 thin films

Ge_x Sb_40−x Se₆₀ (x = 0, 2.42 and 23.41 at.%) thin chalcogenide films were deposited on glass and quartz substrates by the conventional thermal evaporation technique at 300 K. The chemical composition of the bulk material and as-deposited films were determined by energy dispersive analysis X-ray spectrometry (EDAX). X-ray diffraction pattern (XRD) of Ge_x Sb_40−x Se₆₀ (x = 0, 2.42 and 23.41 at.%) thin films indicates that they have amorphous structure. The optical transmission and reflection spectra were measured in the range of 500 to 2500 nm. The optical absorption coefficient spectra were studied for deposited samples. It is observed that the optical absorption edge shift to higher energy range, as the germanium content, x, increases in the film. The type of electronic transition, responsible for the optical properties, is indirect allowed transition. It is found that the optical band gap increases as the Ge content increases.The average coordination number (N_c) in Ge_x Sb_40−x Se₆₀ films increases, but the number of chalcogenide atoms remains constant. The number of Ge - Se bonds and the average bond energy of the system increase with the increase of the average coordination number. The optical band gap, E_g, increases with the increase of the average coordination number, (N_c). Also the energy gap, E₀₄, is discussed in terms of its relation to the chemical composition. The dispersion of the refractive index (n) is discussed in terms of the Single Oscillator Model (SOM) (Wimple - Didomenico model). The single oscillator energy (E₀), the dispersion energy (E_d) and the optical dielectric constant (?_∞) are also estimated.     

Structural properties of RF-magnetron sputtered Cu2O thin films

Cuprous oxide thin films were produced on soda-lime glass substrates using reactive RF-magnetron sputtering. The influence of deposition parameters and temperature on composition and structural properties of the single layers was extensively studied using X-ray diffraction. The control over microstructure and residual stresses is possible by changing reactive gas pressure and deposition temperature. Fiber textured Cu2O films showing a [100] preferred orientation and a fraction of untextured domains can be obtained: suitable modeling taking this microstructure into account shows the presence of a strong compressive stress decreasing with the temperature. Highly reproducible films can be obtained, whose microstructure is preserved when sputtering on tungsten and zinc oxide substrates.     

ab-initio Study of the properties of Ti1−x−ySixAlyN solid solution

We have studied the electronic, structural, and elastic properties of Ti_1−x−ySi_xAl_yN metastable phase, using first principles calculations based on the density functional theory. These calculations provide the lattice parameter, density of states, cohesive energy, formation energy and elastic constants, when Si and Al atoms replace Ti in the TiN lattice. The calculated values of lattice parameters and elastic constants are generally in good agreement with experiments and compare well with other theoretical results. We show that the trend followed by cohesive energy, formation energy, elastic constants is related to the electronic properties and bonding characteristics of these compounds.     

Continuous multi cycle nanoindentation studies on compositionally graded Ti1−xAlxN multilayer thin films

Two types of Compositionally Graded Multilayer (CGM) films of Ti_1−xAl_xN consisting of 21 layers were synthesized by reactive magnetron co-sputtering technique. The first one begins with a layer of Ti_0.4Al_0.6N from substrate and ends with TiN, whereas exactly a reverse order has been followed in the second one. As deposited CGM films are poly-crystalline with rocksalt structure similar to stoichiometric TiN. Secondary Ion Mass Spectrometry (SIMS) depth profile of the films showed the presence of 21 layers of equal thickness (50 nm) with varying aluminum content in steps. Continuous Multi Cycle (CMC) nanoindentation technique was used to analyze the failure modes of these films. Topographic examination of the indented zone revealed the presence of edge cracks inside and outside the indentation area when the load exceeds beyond 90 mN. The load-displacement profiles of CMC and single indentations exhibited the onset of pop-ins at a depth of ∼200 nm.     

Optical properties of Cd1−xZnxS thin films for CuInGaSe2 solar cell application

The photovoltaic Cd_1−xZn_xS thin films, fabricated by chemical bath deposition, were successfully used as n-type buffer layer in CuInGaSe₂ (CIGS) solar cells. Comprehensive optical properties of the Cd_1−xZn_xS thin films were measured and modeled by spectroscopic ellipsometry (SE), which is proven to be an excellent and non-destructive technique to determine optical properties of thin films. The optical band gap of Cd_1−xZn_xS thin films can be tuned from 2.43 eV to 3.25 eV by controlling the Zn content (x) and deposition conditions. The wider-band-gap Cd_1−xZn_xS film was found to be favorable to improve the quantum efficiency in the wavelength range of 450-550 nm, resulting in an increase of short-circuits current for solar cells. From the characterization of quantum efficiency (QE) and current-voltage curve (J-V) of CIGS cells, the Cd_1−xZn_xS films (x = 0.32, 0.45) were demonstrated to significantly enhance the photovoltaic performance of CIGS solar cell. The highest efficiency (10.5%) of CIGS solar cell was obtained using a dense and homogenous Cd_0.68Zn_0.32S thin film as the buffer layer.     

Carrier induced magnetism in dilute Fe doped Ge1−xSbx thin films

Thin films of Fe_0.01Ge_1−xSb_x (x = 0.01, 0.05, 0.10) alloys were prepared by thermal evaporation technique. Characterization of these thin films was done using High Resolution X-Ray Diffraction (HRXRD), Two Probe Resistivity measurement, Atomic Force Microscopy (AFM) and Magnetic Force Microscopy (MFM) respectively. The resistivity results show that activation energy increases with increase in Sb concentration. The low temperature conduction is explained by Variable Range-Hopping mechanism, which fits very well for the whole temperature range. The Arrhenius plot reveals semiconducting behavior. The AFM images of alloys show almost uniform particle size distribution with average particle size varying from 35 to 60 nm with increase in Sb concentration. The MFM images corresponding to the AFM images show the films exhibiting ferromagnetic interactions at room temperature. The average magnetic domain sizes were observed to increase from 43 to 68 nm with increase in Sb concentration from x = 0.01 to x = 0.10.     

Structural, electrical and optical properties of transparent Zn1 − xMgxO nanocomposite thin films

Zn_1 − xMg_xO thin films of various Mg compositions were deposited on quartz substrates using inexpensive ultrasonic spray pyrolysis technique. The influence of varying Mg composition and substrate temperature on structural, electrical and optical properties of Zn_1 − xMg_xO films were systematically investigated. The structural transition from hexagonal to cubic phase has been observed for Mg content greater than 70 mol%. AFM images of the Zn_1 − xMg_xO films (x = 0.3) deposited at optimized substrate temperature clearly reveals the formation of nanorods of hexagonal Zn_1 − xMg_xO. The variation of the cation-anion bond length to Mg content shows that the lattice constant of the hexagonal Zn_1 − xMg_xO decreases with corresponding increase in Mg content, which result in structure gradually deviating from wurtzite structure. The tuning of the band gap was obtained from 3.58 to 6.16 eV with corresponding increase in Mg content. The photoluminescence results also revealed the shift in ultraviolet peak position towards the higher energy side.     

Microstructure of Co2CrxFe1−xAl thin films for magneto-electronic applications

Thin films of the Heusler alloy Co₂Cr_0.6Fe_0.4Al have been prepared by means of magnetron sputtering under varying conditions (sputter power, sputter pressure and substrate temperature). All the films are polycrystalline with the cubic B2 structure. The extent of Co-Al antisite defects, lattice constants, internal stress states are influenced by the sputter conditions which is related to differences in the saturation magnetization. The magnetic moment can be increased by additional annealing up to an optimum temperature of 400 °C, but does not reach the theoretically predicted value. Above 600 °C the metastable B2 phase transforms into either (ε)-Co/Cr or (α)-Co/Cr.     

Structural and optical properties of rock-salt Cd1 − xZnxO thin films prepared by thermal decomposition of electrodeposited Cd1 − xZnxO2

Cd_1 − xZn_xO nanocrystalline thin films with rock-salt structure were obtained through thermal decomposition of Cd_1 − xZn_xO₂ (x = 0, 0.37, 0.57, 1) thin films which were electrodeposited from aqueous solution at room temperature. X-ray diffraction results showed that the Zn ions were incorporated into rock salt-structure of CdO and the crystal lattice parameters decreased with the increase of Zn contents. The bandgaps of the Cd_1 − xZn_xO thin films were obtained from optical transmission and were 2.40, 2.51, 2.63 and 3.25 eV, respectively.     

Reactively sputtered GaAsxN1−x thin films

Thin films of GaAs_xN_1−x alloys were deposited by reactive rf magnetron sputtering of GaAs target with a mixture of argon and nitrogen as the sputtering gas. Growth rate was found to decrease from ∼ 7 μm/h to ∼ 2 μm/h as the nitrogen content increased from 0% to 40%. XRD and TEM studies of the films reveal the presence of hexagonal GaN with a significant increase of the lattice parameters in a narrow range of composition of the sputtering gas (5-10% nitrogen), which is attributed to the incorporation of arsenic. The limited availability of nitrogen in the sputtering atmosphere is found to encourage the incorporation of arsenic in the alloy films. Optical absorption coefficient spectra of the films were obtained from reflection and transmission data. The effect of arsenic incorporation is seen in the optical absorption spectra of the films, which show a continuous shift of the absorption edge to lower energies with respect to that of gallium nitride.     

Laser-induced amorphization and crystallization on Se80Te20−xPbx thin films

Thin films of glassy alloys of a-Se₈₀Te_20−xPb_x (x=2, 6 and 10) was crystallized in a specially designed sample holder under a vacuum of 10⁻² Pa. The amorphous and crystallized films were induced by pulse laser (wavelength: 337.1 nm, frequency: 10 Hz, pulse duration: 4 ns and pulse energy: 0.963 mJ). After laser irradiation on amorphous and crystalline films: optical band gaps were measured. Crystallization and amorphization of chalcogenide films is accompanied by the change in the optical band gap. The change in optical energy gap could be determined by identification of the transformed phase. This change in the optical band gap may be due to the increase in the grain size and the reduction in the disorder of the system.     

Microstructure and optical properties of MgxZn1−xO thin films grown by means of pulsed laser deposition

The single-phase epitaxial Mg_xZn_1−xO (0.4 < x < 0.9) alloy films with wide band gap have been deposited on cubic LaAlO₃ (LAO) (100) substrates by pulsed laser deposition (PLD). X-ray diffraction measurement and TEM photograph indicate that the cubic phase could be stabilized up to Zn content about 0.6 without any phase separation. Films and substrates have a good heteroepitaxial relationship of (100) _MgxZn1−xO||(100)_LAO (out-of-plane) and (011)_MgxZn1−xO||(010)_LAO (in-plane)_. The lattice parameters a of Mg_xZn_1−xO films increase almost linearly with increasing ZnO composition, while the band gap energy of the materials increases from 5.17 to 5.27 eV by alloying with more MgO. The cross-section morphology reveals layer thickness of about 250-300 nm and AFM scan over a 30 μm × 30 μm area reveals a surface roughness R_a of about 100 nm.     

Determination of optical constants of Cd1−xZnxTe thin films by spectroscopic ellipsometry

The optical response of vacuum-evaporated Cd_1−xZn_xTe thin films in the 1.5-5.6 eV photon energy range at room temperature has been studied by spectroscopic ellipsometry. The films of Cd_1−xZn_xTe (x=0.04) were deposited at room temperature onto well-cleaned glass substrates of film thickness 450 nm. The measured dielectric-function spectra reveal distinct structures at energies of the E₁, E₁+Δ₁ and E₂ critical points corresponding to the interband transitions. Dielectric related optical constants such as complex refractive index, the absorption coefficients and the normal incidence reflectivity, are presented. Results are in satisfactory agreement with the calculations over the entire range of the photon energies.     

Influence of laser-irradiation on the optical constants Se75S25 − xCdx thin films

Amorphous thin films of glassy alloys of Se₇₅S_25 − xCd_x (x = 2, 4 and 6) were prepared by thermal evaporation onto chemically cleaned glass substrates. Optical absorption and reflection measurements were carried out on as-deposited and laser-irradiated thin films in the wavelength region of 500-1000 nm. Analysis of the optical absorption data shows that the rule of no-direct transitions predominates. The laser-irradiated Se₇₅S_25 − xCd_x films showed an increase in the optical band gap and absorption coefficient with increasing the time of laser-irradiation. The results are interpreted in terms of the change in concentration of localized states due to the shift in Fermi level. The value of refractive index increases decreases with increasing photon energy and also by increasing the time of laser-irradiation. With the large absorption coefficient and change in the optical band gap and refractive index by the influence of laser-irradiation, these materials may be suitable for optical disc application.     

Structure and optical properties of AlxZn1−xO alloys by sol-gel technique

Al_xZn_1−xO (x = 0-0.5) thin films were prepared on quartz glass substrates by sol-gel technique. X-ray diffraction (XRD), scanning electron microscope (SEM), and X-ray photoelectron spectroscopy (XPS) were employed for microstructure characterization of these thin films. In films with up to 20 at.% Al incorporation, compound nano-crystal phase was observed while wurtzite structure disappeared. Zn3d electron binding energy and Zn LMM‘s chemical shift were both increased by more than 0.4 eV. Transmittance spectra revealed that these films possessed high transmittance in the visible region, and the end of UV absorption edge shifted to less than 300 nm when Al content exceeds 20 at.% due to quantum confinement effect.     

PZT/ZnO薄膜制备及其结构特性研究

利用固相反应制备的ZnO-Li_(2.2%)陶瓷靶和RF射频磁控溅射技术在Si(100)基片上制备了高度c轴择优取向的ZnO薄膜,XRD和电性能分析表明掺杂Li离子改善了ZnO靶材的结构和性能,同时研究了不同RF溅射温度对ZnO薄膜结构与取向的影响;然后采用sol-gel前驱单体薄膜制备方法,以ZnO为过渡层淀积PZT薄膜,探讨高度c轴(002)择优取向ZnO薄膜对PZT薄膜结构与性能的影响,实验发现在PZT/ZnO异质结构中,致密、均匀和高度c轴择优取向的ZnO可作为晶核,促进PZT钙钛矿结构转化、晶粒(110)择优取向生长,相应降低PZT薄膜的退火温度.     

Compositional dependence on the optical properties of amorphous As2 − xS3 − xSbx thin films

In this paper, we report results of the optical properties of thermally deposited As_2 − xS_3 − xSb_x thin films with x = 0.02, 0.07, 0.1 and 0.15. We have characterized the deposited films by Fourier Transform Infrared, Raman and X-ray photoelectron spectroscopy (XPS). The relationship between the structural and optical properties and the compositional variation were investigated. It was found that the optical bandgap decreases with increase in Sb content. The XPS core level spectra show a decrease in As₂S₃ percentage with increase in Sb content. This is confirmed from the shifting of the Raman peak from AsS₃ vibrational mode towards SbS₃ vibrational mode.