Structural,optical and electrical properties of laser irradiated Pb doped Ga–Se chalcogenide thin films

Using the Transverse Electrical Excitation at Atmospheric Pressure (TEA) nitrogen laser, we had irradiated the amorphous thin films of Ga₁₀Se₈₁Pb₉ chalcogenide glass and the results have been discussed in terms of the structural aspects of Ga₁₀Se₈₁Pb₉ glass. The observed changes are associated with the interaction of the incident photon and the lone-pairs electrons which affects the band gap. The X-ray structural characterization revealed the amorphous nature of as prepared films and polycrystalline nature of the laser irradiated films. The optical band gap of these thin films is measured by using the absorption spectra as a function of photon energy in the wavelength region 400–1200 nm. It is found that the optical band gap decreases while the absorption coefficient increases with increasing the irradiation time. The decrease in the optical band gap has been explained on the basis of change in nature of films, from amorphous to polycrystalline state, with the increase in exposure time. The dc conductivities and activation energies of these thin films are measured in temperature range 303–403 K. It has been found that the activation energy in Ga₁₀Se₈₁Pb₉ chalcogenide thin films decreases whereas the dc conductivity increases at each temperature by increasing the irradiation time.     

Nonlinear Integrated Optical Waveguides in Chalcogenide Glasses

This paper reports on the study and measurement of the third order optical nonlinearity in bulk sulfide-based chalcogenide glasses; The fabrication process of the ultrafast laser deposited As-S-(Se)-based chalcogenide films and optical waveguides using two techniques: wet chemistry etching and plasma etching.     

Thickness distribution of thin amorphous chalcogenide films prepared by pulsed laser deposition

Amorphous chalcogenide thin films were prepared from As₂Se₃, As₃Se₂ and InSe bulk glasses by pulsed laser deposition using a KrF excimer laser. Thickness profiles of the films were determined using variable angle spectroscopic ellipsometry. The influence of the laser beam scanning process during the deposition on the thickness distribution of the prepared thin films was evaluated and the corresponding equations suggested. The results were compared with experimental data.     

Investigations of As-S-Se thin films for use as inorganic photoresist for digital image-matrix holography

As-S-Se chalcogenide thin films are successfully employed in classical and dot-matrix holography as inorganic photoresists for obtaining a relief-phase hologram. However using these films for image-matrix hologram recording has not been studied due to some features of image-matrix technology. For the applied research of the optical properties of As-S-Se films an experimental device of digital image-matrix holographic recording based on 100 mW 405 nm semi-conductor laser and Spatial Light Modulator (SLM) has been created. The device has the following main parameters: 140 × 105 μm frame size; laser intensity during exposure 10 W/cm². With the help of this device diffraction grating and security holograms were recorded on As-S-Se thin films. The work reported herein presents results of an experimental study of how diffraction efficiency (DE) of the received relief-phase holographic gratings depends on an exposure and period. Diffraction grating profiles and speed of etching corresponding to different exposure doses are shown. Hologram samples with DE = 65% have been received which allows for using chalcogenide film as alternative to organic photoresists in applied dot-matrix and image-matrix holography.     

Polarization-dependent laser-induced giant mass transport in glassy semiconductors

Direct experimental evidence of the validity of the two-phase model of chalcogenide glass has been obtained. It has been shown that the polarization-light irradiation of glassy semiconductor films induces giant mass transport in the direction perpendicular to the polarization of the incident light. It has been revealed that a surface relief appears in the irradiated films. The shape of the relief depends on the laser polarization state. A macroscopic model qualitatively describing the observed phenomenon is presented.     

A novel optical diagnostic technique for analyzing the recrystallization characteristics of polycrystalline silicon thin films following frontside and backside excimer laser irradiation

Excimer laser annealing (ELA) is a widely used technique for producing polycrystalline silicon (poly-Si) thin films. An optical inspection system with simple optical arrangements for rapid measurement of recrystallization results of poly-Si thin films is developed in this study. The recrystallization results after both frontside ELA and backside ELA can be easily visible from the profile of peak power density distribution using the optical inspection system developed with an optimized moving velocity of 0.312 mm/s of the specimen. The method of backside ELA is suggested for batch production of low-temperature polycrystalline silicon thin-film transistors due to higher laser beam utilization efficiency and lower surface roughness of poly-Si films.     

Pulsed laser deposition of perovskite relaxor ferroelectric thin films

Structural, dielectric and ferroelectric properties of thin films of La-doped lead zirconate titanate (PLZT) and sodium bismuth titanate-barium titanate (NBT-BT) perovskite relaxor ferroelectric have been investigated. PLZT films were deposited on Pt/Si substrates in oxygen atmosphere by pulsed laser deposition (PLD) and radio frequency (RF) discharge-assisted PLD, using sintered targets with different La content and Zr/Ti ratio, near or at the boundary relaxor ferroelectric. The films are polycrystalline with perovskite cubic or slightly rhombohedral structure. A slim ferroelectric hysteresis loop, typical for relaxors, has been measured for all film sets. Dielectric characterization shows a large value of capacitance tunability and low dielectric loss. However, common problems related to lead diffusion into the metallic electrode layer do not allow one to obtain high capacitance values, due to the formation of an interface layer with low dielectric constant. Lead-free NBT-BT thin films have been deposited on single crystal (1 0 0)-MgO substrates starting from targets with composition at the morphotropic phase boundary between rhombohedral and tetragonal phase. Films deposited by PLD are polycrystalline perovskite with a slight (1 0 0) orientation. Capacitance measurements were performed using interdigital metallic electrodes deposited on the film's top surface and showed high relative dielectric constant, on the order of 1300.     

Studies on thin films of lead chalcogenides

A good deal of information regarding the synthesis and opto–electro-structural properties of thin films of lead chalcogenides have been revealed. The development of laser technology had opened up new application for narrow gap lead salts and their alloys. The polycrystalline thin films were deposited onto optically plane and chemically clean glass substrates by vacuum evaporation technique. The films were thin, uniform, smooth and tightly adherent to the substrates.Optical absorption spectroscopy, X-ray diffraction technique and current–voltage characteristics method were used to characterize the films. The absorption coefficients and optical band gaps of films were determined by using FTIR spectrophotometer. The nature of sample, crystal structure and lattice parameters of films were found from X-ray diffractograms. The dc conductivities and activation energies of films were measured in temperature range 300–380 K. Schottky junctions of PbS, PbSe and PbTe with indium metal were made. The barrier heights and ideality factors of these metal–semiconductor junctions were determined by using I–V characteristics.     

Photoexpansion and photobleaching effects in oxysulfide thin films of the GeS2+Ga2O3 system

Oxysulfide systems undergo structural transformations upon illumination with laser light of near bandgap energy, as well as chalcogenide materials (glasses and films). In this paper, photoinduced effects such as photoexpansion and photobleaching were observed in GeS₂+Ga₂O₃ (GGSO) films synthesized by electron beam evaporation. A surface expansion of the thin films and a shift to shorter wavelengths of the optical absorption edge were observed as a result of UV laser irradiation (wavelength of 351 nm) and they are dependent on laser power density, exposure time and film composition. These parameters were varied to evaluate and enhance the observed effects. In addition, the irradiated GGSO samples exhibited a decrease in refractive index, measured with a prism-coupling technique, which makes these films suitable candidates for applications as gratings and waveguides in integrated optics.     

利用磁控溅射技术在熔融石英衬底上生长铟锡氧薄膜的结构和形貌特性研究

利用磁控溅射技术在熔融石英衬底上沉积铟锡氧薄膜(ITO),讨论了生长温度、沉积时间、激光辐照和退火对ITO薄膜结构及形貌的影响.随着沉积温度的升高和沉积时间的延长,薄膜的晶化程度得到明显的改善,方块电阻降低,并且薄膜的形貌从光滑表面的圆形多晶颗粒演变到枝杈形貌.短时间的脉冲激光辐照使得枝杈的尖状晶粒变得圆滑,导电性略有改善.ITO薄膜在可见光区的透过率在经过空气中退火处理后明显得以改善,平均透过率可以达到80%.     

Indium and tin oxide polycrystalline thin films as NO gas sensors produced by reactive pulsed laser ablation and deposition

Pulsed laser ablation is a very interesting method of depositing thin films of several materials and compounds, such as oxides, nitrides, insulators, semiconductors, and superconductors. Indium and tin oxide polycrystalline thin films have been grown on silicon (100) substrates by reactive PLD from two metallic targets of indium and tin by multilayered deposition, in the presence of oxygen, using a frequency-doubled Nd-YAG laser (5=532 nm). The films produced have been studied to evaluate their use as NO gas sensors, and the best performance has been found by varying some important parameters, such as the substrate temperature and the pressure of oxygen in the deposition chamber. X-ray diffraction analysis of the deposited films shows that they are polycrystalline with a preferential (400) orientation. Electrical resistivity measurements, performed by using a four-point probe technique, show a sharp increase in resistivity when the films are exposed to NO. The electrical responses of tin oxide-indium oxide multilayered thin films are reported.     

Evolution of microstructure in polycrystalline silicon thin films upon excimer laser crystallization

Polycrystalline silicon (poly-Si) films fabricated by pulsed excimer laser crystallization (ELC) have been investigated using time-resolved optical measurements, scanning-electron microscopy, and cross-sectional transmission-electron microscopy. Detailed crystallization mechanisms are proposed to interpret the microstructure evolution of poly-Si films for both frontside and backside ELC. It is found that the backside ELC is a good candidate for the manufacturing of low-temperature polycrystalline silicon because of the high laser efficiency and low surface roughness of the poly-Si films.     

Laser-induced changes on optical band gap of amorphous and crystallized thin films of Se75S25−xAGx

Optical band gap of amorphous, crystallized, laser induced amorphous and laser induced crystallized films of Se₇₅S_25−xAg_x (x=4, 6 and 8) glassy alloys was studied from absorption spectra. The amorphous and crystallized films were induced by pulse laser for 10 min. After laser irradiation on amorphous and crystalline films, optical band gap was measured. It has been found that the mechanism of the optical absorption follows the rule of indirect transition. The amorphous thin films show an increase in the optical band gap, while the crystallized (thermally annealed) thin films show a decrease in the optical band gap by inducing laser irradiation. Crystallization and amorphization of chalcogenide films were accompanied with the change in the optical band gap. The change in optical energy gap could be determined by identification of the transformed phase. These results are interpreted in terms of concentration of localized states due to shift in Fermi level.     

Femtosecond pulse crystallization of thin amorphous hydrogenated films on glass substrates using near ultraviolet laser radiation

Femtosecond laser treatments (second harmonic of Ti-sapphire laser, λ ≈ 400 nm wavelength, <30 fs pulse duration) were applied for crystallization of thin hydrogenated amorphous silicon films on glass substrates. The concentration of atomic hydrogen in the films was varied from 10 to ≈35%. The energy densities (laser fluences) for crystallization of the films with thicknesses from 20 to 130 nm were found. Assumedly, non-thermal processes (plasma annealing) take place in phase transition caused ultra-fast pulses. The developed approach can be used for creation of polycrystalline silicon films on non-refractory substrates.     

不同沉积参量下ZrO2薄膜的微结构和激光损伤阈值

ZrO2采用X射线衍射(XRD)技术分析了不同充氧条件和沉积温度对ZrO2溥膜组成结构的影响,并对不同工艺下制备的薄膜的表面粗糙度和激光损伤阈值进行了测量。结果发现随着氧压的升高,ZrO2溥膜将由单斜相多晶态逐渐转变为非晶态结构,而随着基片温度的增加,溥膜将由非晶态逐渐转变为单斜相多晶态。同时发现随着氧压升高晶粒尺寸减小,而随着沉积温度增加,晶粒尺寸增大。氧压增加时工艺对表面粗糙度有一定程度的改善,而沉积温度升高,工艺对表面粗糙度的改善不明显。晶粒尺寸大小变化与表面粗糙度变化存在对应关系。激光损伤测量表明,氧压条件和沉积温度对ZrO2薄膜的抗激光损伤能力有着较大影响。     

Study of the nonlinear refractive index of chalcogenide films by the <Emphasis Type="Italic">RZ</Emphasis>-scan method

Results of studying nonlinear refraction of chalcogenide films by the RZ-scan method with the use of radiation of a picosecond Nd:YAG laser (λ = 532 nm) are presented. The sign of the nonlinear refractive index is analyzed with the help of the Kramers-Kronig relations. Mechanisms of nonlinear refraction in materials are discussed.     

Photoassisted chemical solution deposition method for fabricating uniformly epitaxial VO2 films

Epitaxial VO₂ films were prepared on the TiO₂ (001) substrates by the excimer-laser-assisted metal–organic deposition (ELAMOD). The quality of the epitaxial films obtained by irradiation with a KrF laser was found to be affected by the film structure obtained after preheating at 500 or 300°C. When the films containing crystal domains, which were obtained by preheating at 500°C, were irradiated with the laser at room temperature under a base pressure of 250 Pa, epitaxial and polycrystalline VO₂ phases were simultaneously formed. In contrast, when the amorphous films containing organic components, which were obtained by preheating at 300°C, were irradiated with the laser at room temperature in air, a single phase of epitaxial VO₂ was formed. By using thermal simulations, we determined that the formation of the epitaxial phase was affected both by the temperature distribution within the film during the laser irradiation and by the laser intensity at the interface between the substrate and the film. The latter factor is considered to play a role in the nucleation of crystallization, causing the epitaxial phase to form preferentially compared to the polycrystalline phase in the amorphous matrix of the films. These results indicate that the ELAMOD process is effective for the fabrication of epitaxial VO₂ films at low temperature.     

532nm连续激光晶化非晶硅薄膜的原位拉曼光谱研究

用磁控溅射制备了非晶硅薄膜,用波长为532 nm的连续激光退火和显微Raman光谱原位测试技术和场发射扫描电子显微镜研究了非晶硅薄膜在不同激光功率密度和不同扫描速度下的晶化状态。结果表明,激光照射时间10 s,激光功率密度大于2.929×105W/cm2时,能实现非晶硅薄膜晶化。在激光功率密度为5.093×105W/cm2,扫描速度为10 mm/s时非晶硅开始向多晶硅转化。在5.093×105W/cm2的功率密度下,以1.0 mm/s的扫描速度退火非晶硅薄膜,得到的晶粒直径为740 nm。     

Characterization of pulsed laser deposited chalcogenide thin layers

In this work we report on pulsed laser deposition (PLD) of chalcogenide thin films from the systems (AsSe)_100−xAgI_x and (AsSe)_100−xAg_x for sensing applications. A KrF* excimer laser (λ = 248 nm; τ_FWHM = 25 ns) was used to ablate the targets that had been prepared from the synthesised chalcogenide materials. The films were deposited in either vacuum (4 × 10⁻⁴ Pa) or argon (5 Pa) on silicon and glass substrates kept at room temperature. The basic properties of the films, including their morphology, topography, structure, and composition were characterised by complementary techniques. Investigations by X-ray diffraction (XRD) confirmed the amorphous nature of the films, as no strong diffraction reflections were found. The film composition was studied by energy dispersive X-ray (EDX) spectroscopy. The morphology of the films investigated by scanning electron microscopy (SEM), revealed a particulate-covered homogeneous surface, typical of PLD. Topographical analyses by atomic force microscopy (AFM) showed that the particulate size was slightly larger in Ar than in vacuum. The uniform surface areas were rather smooth, with root mean square (rms) roughness increasing up to several nanometers with the AgI or Ag doping. Based upon the results from the comprehensive investigation of the basic properties of the chalcogenide films prepared by PLD and their dependence on the process parameters, samples with appropriate sorption properties can be selected for possible applications in cantilever gas sensors.     

纳秒激光作用下二氧化钒薄膜相变特性

采用脉冲激光沉积法制备了VO2薄膜,应用X射线衍射和X射线光电子能谱分析表明样品为多晶薄膜。采用泵浦-探针方法研究了二氧化钒薄膜的相变特性,实验结果表明当激光重复频率为160 Hz时,样品最小相变响应为12ns,相变恢复时间与激光能量按照自然指数关系变化。仿真结果表明当激光能量一定时,二氧化钒薄膜相变恢复时间与衬底材料的热导率、热扩散系数有关。