Photosensitivity Of Films Research Articles

Effect of heat treatment in sulfur on structural, optical and electrical properties of thermally evaporated In2S3 thin films

Crystallinity, optical band gap, resistivity and photoresponse of thermally evaporated In2S3 thin films deposited at a temperature of 350 °C and further annealed in sulfur vapour at different temperature range of 200–300 °C is investigated. It is observed that with an increase of annealing temperature, predominantly β-In2S3 phase is formed and the optical band gap for indirect allowed transitions increases from 1.6 eV to 2.0 eV and for direct allowed transitions from 2.3 eV to 2.7 eV. The electrophysical properties indicate that the activation mechanism of conductivity with an activation energy in the range of 0.5–0.73 eV, which is typical for the presence of indium vacancies in the β-In2S3 crystal structure and for the replacement of sulfur by oxygen atoms. It is also noted that sulfur annealing at temperatures of 250–300 °C leads to an increase in the conductivity and photosensitivity of films, which is suitable for photovoltaic applications.

Annealing induced photosensitivity modulation of zinc selenide thin film in the sub-band gap optical absorption region

The photosensitivity of the chemical bath deposited zinc selenide (ZnSe) thin film of bandgap 2.8 eV air annealed at different temperatures has been studied under sub-band gap optical illuminations of photon energies 1.77, 1.91, and 2.07 eV, respectively. The study reveals significant and systematic changes in the photocurrent even when the photon energy is restricted well below the band gap energy of the material. In addition, the photocurrent decreases more or less exponentially with the annealing temperature, although the absorption coefficients of the annealed samples in the sub-band gap region are seen to be enhanced compared to the as-deposited sample. The XRD measurements show the cubic phase of ZnSe, accompanying additionally the orthorhombic ZnSeO3 crystallites in the deposited film. The study further reveals comparatively stronger crystalline improvement of the ZnSeO3 crystals than the cubic ZnSe crystals upon annealing. The observed photosensitivity of the film is compared to that of the cadmium sulphide film deposited by a chemical bath deposition technique and found to be sharply contrasting in behavior. We attribute the unusual photosensitivity of the ZnSe film to ZnSeO3 crystallites which act simultaneously as self generators and absorbers of photoelectrons in the ZnSe crystals, without effectively contributing to the overall photoconductivity of the material.

High‐performance a‐SiGe:H thin film prepared by plasma‐enhanced chemical vapor deposition with high plasma power for solar‐cell application

AbstractHydrogenated amorphous silicon germanium (a‐SiGe:H) thin films were prepared by a 13.56‐MHz plasma‐enhanced chemical vapor deposition (PECVD) method. The optical, optoelectronic, and microstructure properties of the a‐SiGe:H thin films prepared with different plasma powers were investigated systematically by transmission, photo/dark conductivity, Raman, and Fourier transform infrared (FTIR) spectroscopy measurements. It was found that when the deposition pressure was high and the hydrogen (H2) dilution ratio ([H2]/([SiH4] + [GeH4])) was low, an appropriate high plasma power could enlarge the optical bandgap (Eg) by reducing the Ge content in the thin film, enhance the film photosensitivity by improving the film microstructure, and increase the film growth rate. As a demonstration, excellent a‐SiGe:H thin film with Eg of 1.5 eV, the photosensitivity of above 104 and a growth rate of 6.6 Å s−1 was successfully fabricated for the solar‐cell application with a plasma power density of 400 mW cm−2, a deposition pressure of 3 Torr, and a H2 dilution ratio equal to 3 at 220 °C. The underlying mechanism was further analyzed.

Effect of Ge Incorporation on Hydrogenated Amorphous Silicon Germanium Thin Films Prepared by Plasma Enhanced Chemical Vapor Deposition

Hydrogenated amorphous silicon germanium thin films (a-SiGe:H) were prepared via plasma enhanced chemical vapor deposition (PECVD). By adjusting the flow rate of GeH4, a-SiGe:H thin films with narrow bandgap (Eg) were fabricated with high Ge incorporation. It was found that although narrow Eg was obtained, high Ge incorporation resulted in a great reduction of the thin film photosensitivity. This degradation was attributed to the increase of polysilane-(SiH2)n, which indicated a loose and disordered microstructure, in the films by systematically investigating the optical, optoelectronic and microstructure properties of the prepared a-SiGe:H thin films via transmission, photo/dark conductivity, Raman spectroscopy, and Fourier transform infrared spectroscopy (FTIR) measurements. Such investigation provided a helpful guide for further preparing narrow Eg a-SiGe:H materials with good optoelectronic properties.

Photosensitivity Characterization of Nanostructured Tin Oxide Films and Alternative Photodetector Application

In this paper, we present an analysis of the photosensitivity property of electrical resistance of nanostructured porous tin oxide films (SnO2) deposited on Si substrates using a spray method. Based on this property, we propose a new application for this material as an element in a photodetector device. As we verified that the film photosensitivity is influenced by room temperature, to develop a photodetector device, we propose a microcontroller-based algorithm for compensating temperature changes in a certain range. The morphological and chemical structure of the sample films revealed by atomic force microscopy (AFM) and Raman spectroscopy are also discussed. The dynamics of the photodetector have been tested by varying the frequency of light excitation and the temperature of the film. The results show that the device works properly for intermediate ranges of frequency and temperature, but its response degrades as the frequency or temperature rises.

High Efficient Photoinitiator of Hexaphenylbisimidazole Derivatives with Substituents in the 2-Phenyl Ring

Hexaphenylbisimidazoles with methoxy and nitro substituent in 2-phenyl ring were synthesized and evaluated by UV-vis absorption spectrum, photo-dilatometer and photoresist dry film. Both methoxy and nitro group shift the UV-vis absorption spectra of HABIs to a longer wavelength by comparison with the parent HABIs. The UV-vis absorption spectrum of B1-HABI exhibits a 13nm redshift than TCTM. Photo-dilatometer experiments indicate that their photoinitiating efficiencies are higher except B3-HABI. The dry film photosensitivity of B1-HABI at 365nm and 405nm are much better than traditional HABIs.

Photosensitivity of holographic recording media based on films of polymer compositions with cadmium sulfide nanoparticles

The effect of doping with CdS nanoparticles of recording medium films for the thermoplastic holographic recording process, which are based on photosemiconductors (oligomers and cooligomers of glycidylcarbazole) and a dielectric (a styrene copolymer with octyl methacrylate) containing a photoconductivity sensitizer, on their photosensitivity was studied. The enhancement of photosensitivity of films by doping with nanoparticles is associated with the appearance of an additional channel for transport of electrons generated from sensitizer molecules. A difference in informational properties between the oligomer and the polymer films was revealed.

The influence of hydrazine hydrate on the photoconductivity of PbS thin film

High quality poly crystalline nanostructured PbS thin film has been deposited on a glass substrate by chemical deposition technique. The hydrazine hydrate as a reducing agent for lead ion has been used for preparation of the film. After deposition, the film has been annealed, and then the influence of hydrazine hydrate on the dark resistivity and photosensitivity of film have been investigated. It was found that in the presence of hydrazine hydrate in chemical deposition bath, the resistance of the prepared film increases to mega ohm. The measured room temperature detectivity of the film is 4 × 10 9 W −1 Hz 1/2 cm at the wavelength of 2.4 μm. The experimental results have shown that the PbS film, which has been prepared according to this procedure, can be applied as an infrared detector in the range of 1.0–3.0 μm.

Unusual photoelectric properties of polymeric composites containing heteropolynuclear complexes of transition metals

Composites based on acrylonitrilebutadienestyrene and poly-N-epoxypropylcarbazole doped with heteropolynuclear copper complexes were synthesized. The electric and photoconductive properties of films of these composites are studied. The absorption and internal photoelectric effect in the visible region of the spectrum are controlled by the d-d transitions of Cu (II) ions. Positive and anomalous negative photoconductivity effects were detected in films of these composites. Unusual photoelectric properties can be caused by nonequilibrium-carrier capture by deep traps near the boundaries of the associations of structurally different complexes. The negative photoconductivity effect is leveled, and film photosensitivity increases as an additional channel of excess hole transport is formed using poly-N-epoxypropylcarbazole. A phenomenological model of the photo-conductivity kinetics that explains the experimental results, is suggested.

Holographic recording media based on polymer compositions with Fe2O3, ZnO, and CdS nanoparticles

We investigated the influence of additions of Fe2O3, ZnO, and CdS nanoparticles in films of holographic recording media based on photosemiconductors (oligomers and co-oligomers of glycidyl carbazole) and a dielectric (copolymer of styrol with octylmethacrylate) that contain an organic compound with intramolecular charge transfer as a sensitizer of photoconductivity in the visible and near-IR regimes on their photoconducting and thermoplastic properties. The photoconduction current for light wavelengths larger than the red boundary of absorption of the nanoparticles is determined by the photogeneration of charge carriers from the sensitizer molecules and by their transport inside and between nanoparticles. The increase in the photosensitivity of films on addition of nanoparticles is attributed to the appearance of an additional channel for the transport of the electrons generated from the photogeneration centers. A new difference between the rheological properties of the films based on organic photosemiconductors and dielectrics has been revealed.

Photoelectric properties of ZnO films doped with Cu and Ag acceptor impurities

The influence exerted by doping with Cu and Ag acceptor impurities at a content of 1, 3, and 5 at. % on the luminescence and photoconductivity of zinc oxide films has been studied. Electron-beam evaporation in optimal modes has been used to obtain films with predominant luminescence in the UV spectral range. It has been shown that the incorporation of copper yields three types of point defects in ZnO: CuZn (3d10), CuZn (3d9), and Cui; and in silver, a single type: AgZn (3d10). Precipitation of a silver oxide phase at the highest impurity concentration has been observed. Impurity incorporation leads to a pronounced increase in the resistance and photosensitivity of films.

Electrical and photoelectric properties of a-Si:H layered films: The influence of thermal annealing

The electrical and photoelectric properties of layered a-Si:H films obtained by cyclic plasmochemical deposition and the effect of thermal annealing on these properties have been studied. Unannealed films demonstrate high photosensitivity, with a photoconductivity to dark conductivity ratio of K=3.4×106. Increasing the annealing temperature causes the film photosensitivity to fall because of a considerable decrease in the photoconductivity and increase in the dark conductivity. For films annealed at temperatures above 500°C, the conductivity is the sum of the band conductivity and the hopping conductivity via states at the Fermi level.

Photo-Induced and Electrooptic Properties of (Pb,La)(Zr,Ti)O3 Films

AbstractPhoto-induced changes in the hysteresis behavior of sol-gel derived Pb(Zr,Ti)O3 (PZT) and (Pb,La)(Zr,Ti)03 (PLZT) films have been characterized. The film photosensitivity has been evaluated with respect to the magnitude of the effects, the time response and the spectral dependence. Photo-induced hysteresis changes exhibit a stretched-exponential time dependence, which implies a dispersive mechanism. The spectral dependence is strongly peaked at the band edge (∼3.4 eV), which indicates that generation of electron-hole pairs in the material is critical. The photo-induced hysteresis changes are reproducible and stable, which indicates that the controlling charge traps are stable. However, improvements in film photosensitivity will be required to develop these materials for optical memory applications.

New way for high-rate a-Si deposition

Preparation of a-Si:H films using Jet PACVD method has been examined. Standard deposition conditions resulted in growth rates in order of 1 nm/s. Photosensitivity of films up to 6 orders of magnitude has been observed. Features of the deposition method used and deposited film properties are discussed.