Study on AlSb Polycrystalline Films Prepared by Magnetron Sputtering

AlSb polycrystalline thin films were prepared by magnetron sputtering with an improved geometric target, and their structural,electrical and optical properties were studied. The results of XRD measurements suggest that the annealed AlSb thin films are Zinc-blende structure with the average size of about 23～31 nm, and the higher temperature promotes the crystallization of the films. The morphology obtained from the AFM measurements reveals that the surfaces of the films are smooth and the particles are uniform with the average size of about 50 nm. Hall Effect measurements show that AlSb films are p-type semiconductors and the test of temperature dependence of dark conductivity in vacuum indicates the conductivity activation energys are 0.05 eV at low temperature and 0.13 eV at a higher temperature. The optical bandgap for a typical AlSb film is 1.52eV, which is indicated from the optical absorption measurements.

New method for fast morphological characterization of organic polycrystalline films by polarized optical microscopy

A new method to visualize the large-scale crystal grain morphology of organic polycrystalline films is proposed. First,optical anisotropic transmittance images of polycrystalline zinc phthalocyanine（Zn Pc） films vacuum deposited by weak epitaxial growth（WEG） method were acquired with polarized optical microscopy（POM）. Then morphology properties including crystal grain size, distribution, relative orientation, and crystallinity were derived from these images by fitting with a transition dipole model. At last, atomic force microscopy（AFM） imaging was carried out to confirm the fitting and serve as absolute references. This method can be readily generalized to other organic polycrystalline films, thus providing an efficient way to access the large-scale morphologic properties of organic polycrystalline films, which may prove to be useful in industry as a film quality monitoring method.

Effect of Heat Treatment Conditions on Photo sensitivity of CdSexS1-x Polycrystalline Films

The influence of thermal treatment on the lux-ampere characteristics of polycrystalline films from the CdSexS1-x solid solution obtained by the method of thermal evaporation in a vacuum has been investigated. It is shown that at low illumination intensities L μ of electrons increases with a power law μ ~ Lγ, first with the exponent γ > 1, then with γ ≈ 0.5, and their concentration n almost does not change. Starting from the intensity L > 12 - 15 lx, the electron concentration increases strongly n ~ Lβ from β ≈ 3.0, and the parameters n and μ reach relatively high values ~(1015 - 1016) sm-3 and ~(150 - 200) sm2/V·s, however further, at L > 50 lx, a weak dependence of n(L) and μ(L) with β, γ < 1.0 is found. The obtained experimental results are interpreted on the basis of a model of a semiconductor film with intergranular potential barriers when the concentration and barrier mechanisms of photoconductivity operate simultaneously.

Photoelectric State with Long-Term Relaxation in CdTe:(Ag, Cu, Cd) and Sb2Se3:Se Photovoltaic Films

The results of an experimental study of long-term relaxation of the photoelectret state of polycrystalline CdTe:(Ag, Cu, Cd) and Sb2Se3:Se films with an anomalous photovoltaic property are presented. In such films, the residual photovoltage is caused by the separation of photocarriers by the built-in electrostatic field of the near-surface region of space charges and their asymmetric capture by deep levels of impurities or complexes, including impurity atoms and intrinsic defects, both in the bulk and on the surface of crystal grains. It has been shown that in activated films, a two-step exponential temporary relaxation of the initial photovoltage of the order of VAPV ≈ (500-600) V is detected, and only 10% of it experiences long-term relaxation (t ≈ 100-120 min).

Effects of Sn-doping on morphology and optical properties of CdTe polycrystalline films

Sn-doped CdTe polycrystalline films were successfully deposited on ITO glass substrates by close space sublimation. The effects of Sn-doping on the microstructure, surface morphology, and optical properties of polycrys- talline films were studied using X-ray diffraction, scanning electron microscopy, and ultraviolet-visible spectrophotometry, respectively. The results show that the lower molar ratio of Sn and CdTe conduces to a strongly preferential orientation of （111） in films and a larger grain size, which indicates that the crystallinity of films can be improved by appropriate Sn-doping. As the molar ratio of Sn and CdTe increases, the preferential orientation of （111） in films becomes weaker, the grain size becomes smaller, and the crystal boundary becomes indistinct, which indicates that the crystallization growth of films is incomplete. However, as the Sn content increases, optical absorption becomes stronger in the visible region. In summary, a strongly preferential orientation of （111） in films and a larger grain size can be obtained by appropriate Sn-doping （molar ratio of Sn ： CdTe = 0.06 ： 1）, while the film retains a relatively high optical absorption in the visible region. However, Sn-doping has no obvious influence on the energy gap of CdTe films.

Lithium Diffusion and Stress in a Polycrystalline Film Electrode

In the present work, the two-dimensional analytical solution for Li diffusion in grains and grain boundaries of a polycrystalline film electrode is established with consideration of Li-segregation at the grain boundary. The stress field induced by the inhomogeneity of Li con- centration, called chemical stress here for brevity, is analyzed via the finite element simulation. The effects of the grain boundary including its size, its diffusion coefficient as well as the segrega- tion phenomenon on the solute concentration and the chemical stress are examined. It shows that grain boundaries can assist fast diffusion and significantly affect the stress profile in the whole film. It proves that tailoring the grain boundary size or other grain boundary-related parameters may provide an alternative strategy for improving the overall diffusivity and mechanical stability of battery electrodes.

A large-grain-size thick-film polycrystalline diamond detector for x-ray detection

A diamond film with a size of 6×6×0.5 mm^3 is fabricated by electron-assisted chemical vapor deposition. Raman spectrum analysis, x-ray diffraction and scanning electron microscope images confirm the high purity and large grain size, which is larger than 300 μm. Its resistivity is higher than 10^12 W· cm. Interlaced-finger electrodes are imprinted onto the diamond film to develop an x-ray detector. Ohmic contact is confirmed by checking the linearity of its current–voltage curve. The dark current is lower than 0.1 n A under an electric field of 30 k V cm^-1. The time response is 220 ps. The sensitivity is about 125 m A W^-1 under a biasing voltage of 100 V.A good linear radiation dose rate is also confirmed. This diamond detector is used to measure x-ray on a Z-pinch, which has a double-layer 'nested tungsten wire array'. The pronounced peaks in the measured waveform clearly characterize the x-ray bursts, which proves the performance of this diamond detector.

Carrier Transport Across Grain Boundaries in Polycrystalline Silicon Thin Film Transistors

We established a model for investigating polycrystalline silicon（poly-Si） thin film transistors（TFTs）.The effect of grain boundaries（GBs） on the transfer characteristics of TFT was analyzed by considering the number and the width of grain boundaries in the channel region,and the dominant transport mechanism of carrier across grain boundaries was subsequently determined.It is shown that the thermionic emission（TE） is dominant in the subthreshold operating region of TFT regardless of the number and the width of grain boundary.To a poly-Si TFT model with a 1 nm-width grain boundary,in the linear region,thermionic emission is similar to that of tunneling（TU）,however,with increasing grain boundary width and number,tunneling becomes dominant.

Preparation and properties of 0.5BiFeO_(3)-0.5PbFe_(0.5)Nb_(0.5)O_(3)ceramics and polycrystalline films

In this paper,we report the successful growth of 0.5BiFeO_(3)-0.5PbFe_(0.5)Nb_(0.5)O_(3)/SrTiO_(3)/Si(001)heterostructure using RFcathode sputtering in an oxygen atmosphere.The deposited films have been investigated by X-ray diffractometry and spectroscopic ellip-sometry(SE).0.5BiFeO_(3)-0.5PbFe_(0.5)Nb_(0.5)O_(3)films on silicon substrates with a strontium titanate buffer layer are single-phase,polycrystalline with a texture in the 001 direction.The unit cell parameters calculated in the tetragonal approximation were c=4.005±0.001Å;a=3.995±0.001Å.The presence in the films of small unit cell deformation arising from different unit cells parameters of the film and substrate is observed.Dielectric properties and capacitance-voltage characteristics have been measured.The ellipsometric parameters have been obtained.

Total Ionizing Dose Radiation Effects in the P-Type Polycrystalline Silicon Thin Film Transistors

The total ionizing dose radiation effects in the polycrystalline silicon thin film transistors are studied. Transfer characteristics, high-frequency capacitance-voltage curves and low-frequency noises (LFN) are measured before and after radiation. The experimental results show that threshold voltage and hole-field-effect mobility decrease, while sub-threshold swing and low-frequency noise increase with the increase of the total dose. The contributions of radiation induced interface states and oxide trapped charges to the shift of threshold voltage are also estimated. Furthermore, spatial distributions of oxide trapped charges before and after radiation are extracted based on the LFN measurements.

Simulation of M-H Loops in FeCo Polycrystalline Thin Films at Finite Temperatures

We apply the hybrid Monte Carlo （HMC） micromagnetie method to FeCo soft magnetic polycrystalline films and test the new method by comparing with the result worked out by micromagnetics using Landau Lifshitz-Gilbert equations, and the magnetic properties of FeCo films are understood better by carefully considering the effects of polycrystalline microstructures. The hysteresis loops of the FeCo film from low temperature up to 1100K are simulated by the new HMC micromagnetic method.

Photosensitivity Spectra of Thin Films from a CdSexS1-x Solid Solution

The results of a study of the energy spectra of the activation of intrinsic defects of a photosensitive film made from the CdSexS1-x solid solution depending on the conditions of preparation and heat treatment in various media are presented. It is shown that at x = 0.8 cadmium vacancies create a deep level with an activation energy Еv + (0.63 ± 0.02) eV, a complex of chlorine atom with a cadmium vacancy creates a level Еv + (0.43 ± 0.02) eV, as well as the fast recombination center Еv + (0.92 ± 0.02) eV. The formation of selenium vacancies due to the introduction of chlorine and its combination with cadmium leads to the appearance of a sticking level Еc - (0.19 ± 0.02) eV. CdSe0.8S0.2 films can be used to develop light emitting diodes, photo sensors, IR and visible lasers.

Local leakage current behaviours of BiFeO_3 films

The leakage current behaviours of polycrystalline BiFeO3 thin films are investigated by using both conductive atomic force microscopy and current-voltage characteristic measurements. The local charge transport pathways are found to be located mainly at the grain boundaries of the films. The leakage current density can be tuned by changing the post-annealing temperature, the annealing time, the bias voltage and the light illumination, which can be used to improve the performances of the ferroelectric devices based on the BiFeOa films. A possible leakage mechanism is proposed to interpret the charge transports in the polycrystalline BiFeO3 films.

Organic Thin Film Field Effect Transistors with PMMA-GMA Gate Dielectric

We fabricate organic thin films using the copolymer of methyl methacrylate and glycidyl methacrylate （PMMA- GMA） as a gate dielectric with a simple top-contact structure. Copper phthalocyanine （CuPc） TFTs are fabricated and the influences of annealing on the performance are studied. The mobilities increase from 2.5 × 10^3 cm^2/Vs to 4.2 × 10^3 cm^2/Vs and threshold voltages decrease from -18 V to -10 V after annealing. The good performances of the devices approach those obtained with inorganic gate dielectric materials such as silicon dioxide under the same technical conditions. It is fully proven that PMMA-GMA is a competitive candidate as an excellent gate insulation layer.

Fabrication of Poly-Si Thin Film on Glass Substrate by Aluminum-induced Crystallization

Amorphous silicon （ a-Si ） thin films were deposited on glass substrate by PECVD, and polycrystalline silicon （ poly- Si ） thin films were prepared by aluminum- induced crystallization （ AlC ）. The effects of annealing temperature on the microstructure and morphology were investigated. The AlC poly-Si thin films were characterized by XRD, Raman and SEM. It is found that a-Si thin film has a amorphous structure after annealing at 400℃ for 20 min, a-Si films begin to crystallize after annealing at 450 ℃ for 20 min, and the crystallinity of a-Si thin films is enhanced obviously with the increment of annealing termperature.

Infrared laser-induced fast photovoltaic effect observed in orthorhombic tin oxide film

The SnO_2/SnO with an orthorhombic structure is a material known to be stable at high pressures and temperatures and expected to have new optical and electrical properties. The authors report a new finding of the infrared laser induced a fast photovoltaic effect arising from orthorhombic tin oxide film with an indirect band gap（~2.4 e V） which is deposited by pulsed laser deposition. The rising time of the photovoltaic signal is about 3 ns with a peak value of 4.48 mV under the pulsed laser beam with energy density 0.015 m J/mm^2. The relation between the photovoltages and laser positions along the line between two electrodes of the film is also exhibited. A possible mechanism is put forward to explain this phenomenon.All data and analyses demonstrate that the orthorhombic tin oxide with an indirect band gap could be used as a candidate for an infrared photodetector which can be operated at high pressures and temperatures.

Selected area laser-crystallized polycrystalline silicon thin films by a pulsed Nd:YAG laser with 355 nm wavelength

Selected area laser-crystallized polycrystalline silicon （p-Si） thin films were prepared by the third harmonics （355 nm wavelength） generated by a solid-state pulsed Nd：YAG laser. Surface morphologies of 400 nm thick films after laser irradiation were analyzed. Raman spectra show that film crystallinity is improved with in- crease of laser energy. The optimum laser energy density is sensitive to the film thickness. The laser energy density for efficiently crystallizing amorphous silicon films is between 440-634 mJ/cm^2 for 300 nm thick films and between 777-993 mJ/cm^2 for 400 nm thick films. The optimized laser energy density is 634, 975 and 1571 mJ/cm^2 for 300, 400 and 500 nm thick films, respectively.

Polycrystalline GaSb thin films grown by co-evaporation

We report optical and electrical properties of polycrystalline GaSb thin films which were successfully grown by co-evaporation on soda-lime glass substrates. The thin films have preferential orientation of the （111） direction. SEM results indicate that the average grain size of GaSb thin film is 500 nm with the substrate temperature of 560 ℃. The average reflectance of GaSb thin film is about 30% and the absorption coefficient is of the order of 10^4 cm^-1. The optical bandgap of GaSb thin film is 0.726 eV. The hole concentration shows a clear increasing trend as the Ga-evaporation-temperature/Sb-evaporation-temperature （TGa/Tsb） ratio increases. When the Ga crucible temperature is 810 ℃ and the antinomy crucible temperature is 415 ℃, the hole concentration of polycrystalline GaSb is 2 × 10^17 cm^-3 and the hole mobility is 130 cm^2/（V·s）. These results suggest that polycrystalline GaSb thin film is a good candidate for the use as a cheap material in TPV cells.

Aluminum induced crystallization of strongly (111) oriented polycrystalline silicon thin film and nucleation analysis

A polycrystalline silicon thin film was fabricated on glass substrate by means of aluminum induced crystallization (AIC). Al and α-Si layers were deposited by magnetron sputtering respectively and annealed at 480°C for 1 h to realize layer exchange. The polycrystalline silicon thin film was continuous and strongly (111) oriented. By analyzing the structure variation of the oxidation membrane and lattice mismatch between γ-Al2O3 and Si, it was concluded that aluminum promoted the formation of (111) oriented silicon nucleus by controlling the orientation of γ-Al2O3, which was formed at the early stage of annealing.

Structural and optical properties of polycrystalline CdS thin films deposited by electron beam evaporation

Highly crystalline and transparent cadmium sulphide （CdS） films were deposited on glass substrate by electron beam evaporation technique. The structural and optical properties of the films were investigated. The X-ray diffraction analysis revealed that the CdS films have a hexagonal structure and exhibit preferred orientation along the （002） plane. Meanwhile, the crystalline quality of samples increased first and then decreased as the substrate temperature improved, which is attributed to the variation in film thickness. UV-vis spectra of CdS films indicate that the absorption edge becomes steeper and the band gap present fluctuation changes in the range of 2.389-2.448 eV as the substrate temperature increased. The photoluminescence peak of the CdS films was found to be broadened seriously and there only emerges a red emission band at 1.60 eV. The above results were analyzed and discussed.