NbSe2, serving as a 2D metal electrode, has been proven to form a Schottky heterojunction with MoSe2 to realize a highperformance broadband photodetector. Here, we further investigated the effect of gate voltage on the optoelectronic characteristics of the device. The results revealed that NbSe2 exhibits a weak electrostatic screening effect similar to graphene, and due to the high-quality contact between the 2D metal and semiconductor, the rectification ratio of the device can be significantly modulated from 0.32 to 5.5×104. Regarding the photovoltaic response characteristics of the device, the gate voltage similarly achieves significant modulation of the short-circuit current (20 nA-1.6 μA), open-circuit voltage (0-0.32 V), maximum electrical power (0-210 nW). Furthermore, the response speed of the device is also influenced by the gate voltage. This work demonstrates that Schottky heterojunctions constructed based on 2D metals can achieve effective control of optoelectronic properties, and has encouraging prospects in the fields of optical communications, optical sensing, and imaging.
Lead selenide telluride (PbSeTe) polycrystalline films were prepared by magnetron sputtering technique using ternary target material. The lead selenide telluride films were oxidized and iodized. The film samples were tested by the Rigaku Smartlab (grazing X-ray diffractometer) in Japan. The morphology of PbSeTe films after evaporation was observed by SEM (Geminisem 300). The Raman spectra of Pb Se telluride thin films were measured by a confocal microprobe Raman spectrometer (RENISHAW in Via Raman Microscope) and a He-Ne laser with wavelength of 514.5 nm. The infrared photoelectric characteristics of the detector made of PbSeTe thin film before and after sensitization were tested and analyzed. XRD and EDS results show that the prepared PTE films are homogeneous and compact with small grains, and no particles with clear edge profiles can be observed under scanning electron microscopy. The atomic ratio of Te, Pb and Se tends to be 5:7:7. The photoelectric performance detection results show that the sensitized device has excellent photoelectric performance, the photocurrent and response speed are improved significantly, and the fastest rise time and fall time of 980 nm can reach 38.95 microseconds and 620 microseconds, respectively, and the maximum signal-to-noise ratio is nearly 100 times. Therefore, by adjusting sputtering parameters and post-processing, PbSeTe thin film detectors with good photoelectric properties can be obtained.
Benefiting from its advantages such as wide tunable bandgap, solution synthesis, and substrate selection diversity, Lead Selenide Colloidal Quantum Dots (PbSe CQDs) has gradually been selected as a highly competitive candidate material for next-generation low-cost, flexible, and broad-spectrum photodetectors. At present, PbSe CQDs-based photodetectors with photoconductive structures have the problems of large dark current and slow photoresponse. However, the manufacturing process of photovoltaic field effect transistors and two-dimensional material quantum dot hybrid structure devices is complicated, and the cost is high. These problems will limit the improvement of the overall performance of the device. For a better performance-cost trade-off, here a junction photodetector is designed using only PbSe, and the device is fabricated on oxygen-silicon substrate. Its response speed is significantly higher than that of photoconductive devices, especially the dark recovery speed is one order of magnitude higher than that of PbS devices with the same structure, while maintain a D* similar to the two-dimensional quasi-zero-dimensional hybrid structure. The findings have inspirational meaning for the design of future advanced CQDs photodetectors.
In the field of electronic modulation, vanadium dioxide (VO2) is a potential material owing to its function of automatic insulator-to-metal transition (MIT) which can induce rapid changes in electrical resistivity through MIT. Nevertheless, the application of modulator based on VO2 is limited by some performance shortcomings, including wide hysteresis loop width (ΔH), high phase transition temperature (Tc) as well as low phase transition amplitude (AMIT). In this work, by DC (DirectCurrent)-magnetron sputtering with doping Fe3+ into VO2 films, narrowed ΔH and decreased Tc are observed. Interestingly, the Fe doped VO2 films show ultra-high phase transition amplitude despite the low Tc due to the influence of Fe dopants. Specifically, the 0.5% Fe-doped VO2 film shows the best MIT characteristics with ultra-high phase transition amplitude of 104, narrow ΔH decreased to 9.8° and low Tc around 60.02°C, which is considered to be the first time to highly heighten the electrical MIT properties by Fe doping. In addition, we also comprehensively studied the influences of doping with Fe element on the MIT properties and microstructures based on characterization such as SEM, XRD, Raman shift and XPS results. These results show that our unique preparation method can manufacture VO2 thin films with excellent MIT properties, which will be beneficial to the popularization and publicity of VO2 based electrical modulator.
Lead sulfide colloidal quantum dots, similar to the nanoscale crystals of most semiconductor crystals, are available in a variety of sizes, shapes, and compositions as well as to make different chemical molecular ligands to modify the surface of the quantum dots and to fabricate functional optoelectronic devices on a variety of substrate materials. The combination of silicon and colloidal quantum dots enables the fabrication of silicon-based compatible quantum dot optoelectronic devices over a wide range of applications. In this paper, the effects of channel doping concentration and channel length on the performance of silicon-based CQD/Si photodetectors are calculated and analyzed from the simulation method. The results show that a suitable doping concentration and a short channel length can improve the performance of the device, which provides a simulation basis for the fabrication of silicon-based compatible arrayed colloidal quantum dot photodetectors.
Terahertz focal plane array imaging technology can realize real-time terahertz imaging with high frame rate. But for a relatively large-sized object imaging, the array scanning should collect a plurality of original image data due to the small-sized focal plane terahertz detector array. In this paper we demonstrate terahertz image preprocessing, image register and image blending in detail. In order to reduce the image noise and enhance the image contrast, we manifest a novel method to preprocess the image by incorporating of Butterworth band-elimination filter and high-frequency nonlinear enhancement methods. Meanwhile, the enhanced image is stitched using the sift algorithm. The experimental result present that the proposed method can accurately mosaic the terahertz grayscale image, which is beneficial to realize the scanning and stitching imaging of large-area objects by focal plane array terahertz detector.
Vanadium dioxide (VO2) films have great potential applications in photoelectric switching, storage devices, terahertz modulators and smart windows, due to the abruptly insulator-metal phase transition (IMT) near room temperature. In this research, vanadium oxide films were deposited by DC reactive magnetron sputtering in different annealing time of 450°C on glass substrates. As for electrical properties, the increasing of annealing time turns out sheet resistance increases at first, and then decreases in insulating phase, vice versa in metallic phase. In optical properties, the visible transmittance of VO2 films initially drops with annealing time prolonging, afterwards the transmittance slightly recovers. Differences between the electrical and optical are due to the grain size. Moreover, VO2 film annealing 15 min presents excellent visible transmittance, highly near-IR modulation efficiency (about 92% at a wavelength of 1100nm) and the lowest phase transition temperature (55.7°C). This result indicates that an appropriate annealing ambient can facilitate the application of VO2 film in smart windows.
A terahertz (THz) microbolometer detector and corresponding real-time imaging system were introduced in this paper. A 10nm NiCr thin film was integrated in the micro-bridge structure as the THz absorption layer by magnetron sputtering and reactive ion etching (RIE), and its improvement of THz absorption was verified by optical characteristics test. Through complicated semiconductor process, a microbolometer detector of 320×240 THz focal plane array (FPA) was prepared. And a real-time imaging system was established to identify the perfomance of this detector. The results demonstrated that the detector could get conscious THz image using a 2.52 THz far-infrared gas laser as THz radiation source.
Doping silicon with chalcogens (S, Se, Te) via femtosecond-laser irradiation lead to increase the absorptance of Si in both visible and infrared region, so chalcogens doped silicon have great potential for use in Si-based optoelectronic devices. Tellurium doped silicon was fabricated by femtosecond-laser irradiation of Si with Si/Te bilayer films. The influence of distance between the sample surface and the laser focus in the process of fabricating micro-structured Si was studied. The results show that the sample surface cannot be located in focal plane, nor is far from the focal plane, suitable distance is necessary to produce regular columnar structure. And the surface structure of doped silicon is vitally important to high absorptance. In addition, we report the dependence of surface morphology and optical properties on scanning speed. The absorptance increases over the entire wavelength as the scanning speed decreases.
Silicon doped vanadium dioxide (VO2) films were successfully prepared on high purity Si(111) substrate. Confirmed by X-ray diffraction, all samples showed a preference orientation of (011) direction. Introducing silicon led grain sizes decreasing comparing to undoped VO2 film, and this result induced a narrow hysteresis width in MIT performance. Furthermore, silicon doped VO2 films annealing in different temperature presented different phase transition properties. In the electrical, a higher annealing temperature resulted in a decrease of sheet resistance and lowering the transition temperature. In terahertz optical transmittance, silicon doped VO2 films keep an excellent modulation ratio, indicating a great potential in the application of terahertz modulator devices.
Vanadium oxide (VOx) thin films were prepared on unheated glass substrate by pulsed dc reactive magnetron sputtering using different pulse frequency. Field emission scanning electron microscopy (FESEM), x-ray photoelectron spectroscopy (XPS) and spectroscopic ellipsometry (SE) measurements were made on the deposited VOx films to characterize the microstructure, composition and optical properties, respectively. It was found that under the same discharge power and argon-oxygen atmosphere, with the increase of pulse frequency, the vertical column-like structure in the films will gradually disappear and the ratio of high-valent VOx to low-valent VOx will obviously elevate. Optical parameters of the VOx films have been obtained by fitting the ellipsometric data (Ψ andΔ) using the Tauc-Lorentz dispersion relation and a multilayer model (air/roughness layer/VOx/glass). The results demonstrated that pulse frequency plays a critical role in determining the transmittance, refractive index, extinction coefficient and optical band gap etc. The correlations between the microstructure, composition, optical properties and pulse frequency are also given by our experiment results. And the mechanisms for the evolution of the microstructure, composition and optical properties with pulse frequency have been discussed. Overall, due to the pulse frequency had a great effect not only on the growth characteristics but also on the optical properties of the VOx films, thus through variation of the pulse frequency during deposition which provide a convenient and efficient approach to control and optimize the performances of the VOx films.
Vanadium oxide (VOx) films were deposited onto well cleaned glass substrates by bipolar pulsed reactive magnetron
sputtering at room temperature. Dependence of the structure, composition, optical and electrical properties of the films
on the pulsed power’s duty cycle has been investigated. The results from the X-ray diffraction (XRD) analysis show that
there was no remarkable change in the amorphous structure in the films with duty cycle can be observed. But chemical
analysis of the surface evaluated with x-ray photoelectron spectroscopy (XPS) indicates that decrease the duty cycle
favors to enhance the oxidation of the vanadium. The optical and electrical properties of the films were characterized by
spectroscopic ellipsometry and temperature dependent resistivity measurements, respectively. The evolution of the
transmittance, optical band gap, optical constants, resistivity and temperature coefficient of resistance (TCR) of the
deposited films with duty cycle was analyzed and discussed. In comparison with conventional DC sputtering, under the
same discharge atmosphere and power level, these parameters of the VOx films can be modified over a broad range by
duty cycle. Therefore adjusting the duty cycle during deposition, which is an effective way to control and optimize the
performances of the VOx film for various optoelectronic devices applications.
This paper designs a ramp generating circuit using for uncooled infrared focal plane arrays (UIRFPA). Compared with the basic ramp generator, the new generator is highly adjustable, easy to operate, and adaptable. By adjusting the total current of the charging circuit, it can realize the ramp wave upper point and slope of the modulation. Current mirror as the discharge load, it can adjust the ramp lower point, and controllable capability. By adjusting accuracy and swing, the new ramp generator for UIRFPA provides a way to adapt to the strength of the infrared scene to control the infrared signal accuracy. Simulation results show that the ramp output swing can be adjusted from 1 V to 4.5 V, a maximum Integral nonlinearity (INL) of 400 µV, a slope distortion lower than 0.01%, linearity higher than 13 bits for the new ramp generator (considering a 4 V input range). At the same time, its good temperature performance shows that the maximum difference of the output voltage is 50 mV in a variety of environments (243 K ~ 333 K). Besides, this circuit has been successfully applied to the infrared system.
In this work, vanadium oxide thin films were grown on glass slides by using reactive direct current (DC) magnetron
sputtering from a vanadium target in an Ar+O2 atmosphere. It was found that the surface morphology, electrical and
optical properties were strongly affected by the deposition temperature. X-ray diffraction (XRD) and scanning electron
microscopy (SEM) were used to characterize the structure and surface morphology of the samples. The structures of
these films showed amorphous nature according to the XRD patterns showing no sharp diffraction peak. Measurements
of SEM indicated the smooth surface of film deposited at low deposition temperature and rough surface at relatively high
deposition temperature. In addition, these surfaces showed no obvious crystalline morphologies, which supported the
XRD results. Electrical measurement indicated that the square resistances of films showed an exponential increase from
33 kΩ/square to 46 MΩ/square as the deposition temperature decreased from 320 to 160 °C, and that the square resistancetemperature
curves of films exhibited typical semiconducting behavior. The investigation of optical properties of films in
near-infrared range indicated that transmittance varied from about 95 % to 55 % when the deposition temperature
elevated. In the ultraviolet-visible range, optical transmission measurements revealed that films showed distinguished
transmission spectra when they were grown at different deposition temperatures. In the range of 300 to 400 nm, a
transmittance shoulder was observed in the spectra, and this shoulder enhanced when the deposition temperature
increased. On the other hand, a transmission enhancement at 530 nm disappeared after the deposition temperature
exceeded 240 °C.
In recent years, TiO2-δ thin films as a kind of thermal sensitive material have been attracting more and more attention on
the application of infrared devices. In this article, TiO2-δ thin films from the technology of DC reactive magnetron
sputtering were deposited on glass substrates under the same sputtering conditions while different annealing conditions.
Annealing effects on electrical properties and thermal sensitivity characteristics were systematically investigated under
different annealing conditions including annealing circumstance, annealing time and annealing temperature. Results
indicated that the sheet resistance (R) and temperature coefficient of resistance (TCR) of TiO2-δ thin films would
decrease after vacuum-annealing and would increase after oxygen-annealing. Furthermore, they would increase more and
more when the annealing time and the oxygen flux increased during oxygen-annealing. On the contrary, R and TCR
would decrease when the annealing temperature went up. Based on that, TiO2-δ thin films could be better applied on
related devices under proper technique of annealing.
Vanadium oxide films were prepared onto glass and KBr substrates at various deposition temperatures by DC reactive
magnetron sputtering. X-Ray photoelectron spectroscopy (XPS), Atomic force microscope (AFM), Fourier transform
infrared spectroscopy (FT-IR) were employed to analyze the VOx films, respectively. Experimental results indicated that
deposition temperature has a great impact on the surface morphology of vanadium oxide films. The XPS analysis
confirmed that the vanadium oxide films prepared are V2O5. From Fourier transform infrared spectroscopy, it can be see
that the infrared active mode corresponding to V-O-V stretching vibration and the stretching vibration of unshared V=O
bonds appeared at about 840 cm-1 and 915 cm-1 in the films formed at 240 , respectively. A shift in the peak position
towards higher frequency was found with increasing the deposition temperature which indicated that the films formed at
higher deposition temperature were structural disorder.
In this article, titanium oxide thin films (TiOx) are prepared with the reactive DC sputtering in an oxygen and argon
atmosphere. Properties of titanium oxide films could be largely varied by controlling the deposition condition. Here we
study on the dependence of sheet resistance, thickness, optical transmittance and film composition of titanium oxide
films on different deposit oxygen flow rates.
On the basis of the brief introduction to theory of uncooled infrared thermal imaging system and the infrared image
processing algorithms, the key technologies to real-time image enhancement was studied, which driving a 160×120
Infrared Focal Plane Arrays (IRFPA) imaging system. In this article, an uncooled infrared thermal imaging system with
real-time image processing and image enhancement was designed and developed, most importantly, a better result was
achieved. Aiming at the Infrared Focal Plane Arrays (IRFPA), the hardware system used flexible design approach and
efficiently developed tools on System-on-a-Programmable-Chip(SOPC)with two SDRAMs memories used as frame
buffers. By this means, the 160 × 120 of IRFPA realized image acquisition. In this article, the structure of the system and
the software realization of infrared images to achievement of the non-uniformity correction and image enhancement
algorithm for parallel operation On the SOPC were described in details.The results showed that the design of SOPCbased
real-time infrared image processing system could simplify system hardware and software design while ensuring
the computing abilitiy. To the IRFPA imaging system of 160 × 120, processed infrared image quality was improved
significantly to meet the real-time dynamic detection and tracking needs. Finally a system of uncooled infrared thermal
imager with high price quality and convenient reconfiguration condition was implemented.
In this article, substoichiometric titanium oxide thin films (TiOX) are prepared with the reactive DC sputtering in an
oxygen and argon atmosphere and then annealed in an oxygen atmosphere. Under a set of optimum deposition
parameters, TiOX film with sheet resistance value of 167.9 KΩ/(box) and TCR value of -3.30%/K obtained. Transmittance of
the optimum film is obtained in the 300≤λ≤1100nm wavelength range at room temperature. Thickness, near-infrared
absorptance, and other properties of the optimum film are also investigated in this paper.
An organic sol-gel method of preparing Mo-doped vanadium oxide thin films was described. Vanadium oxide powder and molybdenum trioxide powder were dissolved into a mixed solution of benzyl alcohol and isobutyl alcohol to obtain a vanadium solution, which was then spin-coated on glass substrates followed by an anneal at 500°C. Square resistance was measured by the four-point probe, and film thickness was measured by the effects of molar ratio. The effects of
doping concentration and film thickness on the electronic properties of vanadium oxide thin film, and film uniformity as well as stability are studied. Results show that the TCR (30°C)
of VO2 films was increased greatly, and the square
resistance was reduced by Mo-doped.
Vanadium oxide (VOx) thin films were deposited on different substrates by reactive DC magnetron sputtering. Silicon
substrate, Si3N4/Si substrate, glass substrate, and α-Al2O3 substrate were adopted in experiments. Results revealed that
the structural features of VOx thin films strongly depend on the substrates. Analysis of square resistance and its
temperature dependence demonstrated that the crystal structure and the growth mode of VOx films play important roles
in the film electrical properties. Experiments demonstrated that substrates have great influence on the growth mode and
thermal resistance properties of VOx thin films.
KEYWORDS: Thin films, Resistance, Temperature metrology, Vanadium, Sputter deposition, Oxides, Atomic force microscopy, Thin film deposition, Scattering, Thin film devices
The dependence of morphology and thermal resistance on the substrate temperature during the deposition of the
vanadium oxide thin films (VOx) was studied. Atomic-force microscopy (AFM) analysis results revealed that the
structural features of VOx thin films strongly depend on the substrate temperature. Analysis of square resistance and its
temperature dependence demonstrated that the difference of morphology introduced by substrate temperature plays an
important role on the electrical properties of the films. The width of the thermal resistance hysteresis loop was also
observed varied with the substrate temperature.
Vanadium oxide thin films of different thickness were deposited on P (100) silicon substrates with silicon nitride thin film layer by reactive DC magnetron sputtering method. The current-voltage (I-V) curves of the samples measured in dark environment and different intensity of light environments showed that photovoltaic effect happened when the films exposed on visible light environments. Square resistance (Rs) and temperature coefficient of square resistance (TCRs) of vanadium oxide thin films were also tested in dark and light environment respectively, and the results demonstrated that the Rs was reduced and TCRs was enhanced when vanadium oxide thin films are exposed on light. Such effects changes with the variation of thickness of vanadium oxide thin films.
In this paper, a series of a-Si:H thin films for about 350 nanometers in thickness were deposited on K9 glass substrate by means of plasma enhanced chemical vapor deposition (PECVD) . During deposition process, there are many factors which influence the optical properties of films. The importance among them includes RF power, substrate temperature and working gas pressure. Technical parameters affect the contents of hydrogen in a-Si:H film. Hydrogen plays a critical role in enhancing the ordering of the film network in a-Si, which can increase nucleation sites and reduce crystallization temperature effectively. The optical constants (n, k) of films were obtained with Forouhi Bloomer (FB) model in spectra ellipsometer (SE) and the absorption coefficient α was deduced from α=4πk/λ.
KEYWORDS: Thin films, Thin film deposition, Plasma enhanced chemical vapor deposition, Refractive index, Atomic force microscopy, Thin film manufacturing, Plasma, Temperature metrology, Manufacturing, Thin film devices
The effect of gas temperature (Tg) on surface morphology, surface roughness, photoelectrical performances of a-Si:H thin films deposited by PECVD at 250°C substrate temperature has been investigated by atomic force microscopy, spectrometric ellipsometry and semiconductor characterization system, respectively. It is found that the surface morphology and density (ρ) as well as the photoelectrical properties such as refractive index (n), dark conductivity (σ), temperature coefficient of resistance (TCR) and activation energy (Ea) remarkably depend on Tg of SiH4 fed in reaction chamber. The higher the Tg, the larger the clusters of a-Si:H thin films deposited. Also, refractive index of a-Si:H thin films increase as Tg rises and the relationship between Tg enhancement of n and the densification of the films is observed. It is indicated that σ varies by two orders of magnitude but TCR decreases by 1.6 %/°C, and Ea gradually decreases linearly from 289.0 to 138.1 meV with Tg varying from room temperature to 160°C. The results of present study suggest that Tg in PECVD chamber plays an important role in the deposition of a-Si:H thin films and directly affects the surface morphology and photoelectrical properties of films. Control of surface morphology, photoelectrical properties of a-Si:H thin films through changing Tg can be usefully applied to the manufacturing of photoelectrical devices.
Amorphous silicon (a-Si:H) films are prepared on K9 glass substrate by plasma enhanced chemical vapor deposition (PECVD) and the substrate temperature varies from 150 to 300 °C. The gas phase processes of pure SiH4 in PECVD system were discussed. The change of grain size and morphology was characterized by atomic force microscope morphology (AFM). The influence of substrate temperature on the growth rate and the optical band gap of Si:H film were measured by spectra ellipsometer (SE). Scanning electron microscopy (SEM) was used to make sure the measurement of film thickness by SE.
Self-assembly as a novel method to prepare ultrathin functional films has drawn more and more attention in recent years. The preparation methods, structure, characterization and NO2 gas sensing properties of polyaniline (PAN) ultrathin films are studied in this paper. Firstly, PAN, bpolyphthalocyanine and polycation were prepared as raw materials for self-assembling PAN ultrathin films. The self- assembled PAN ultrathin flims with polymeric and phthalocyanines were prepared based on doping-induced deposition effect. These films were characterized by UV/visible spectroscopy. The study on self-assembling mechanism show that it is acids that drives the self- assembling process, which is dependent on the PAN solution property, the types of solvents and polymeric acids, the molecular weight of polymers and temperature. At last, the NO2 gas sensing properties is studied in this paper.
Electroactive polyaniline (PANI)/MoO3 nanocomposite ultrathin films were fabricated by a novel molecular self-assembly process based on the alternate deposition of PANI and inorganic polyanion isopolymolybdic acid (IPMA). Unlike the already-used layer-by- layer process based on electrostatic attraction, the process was based on acid-base reaction (or doping) of emeraldine base and IPMA. The process was monitored by UV/Vis spectroscopy and ellipsometry measurement.
A novel sensing material has been developed for constructing a sensor of solvent vapours using chemical
coupling effect of composite, which is different from conventional electron-moving chemiresistors for
use as gas sensors. The composites consisting of polymer loaded with conductive filler near the
percolation threshold exhibit sensitive characters comparable to that of conventional semiconductor gas
sensor but can be realized with much simpler technology and operated at room temperature. This sensor
can also obtain better selectivity by choosing different polymer matrix. Theoretic analysis and
experimental results show sensitive properties of composite sensor greatly depend on composition of
composite and grain size of conducting particles. In general resistance variation R/Rin the presence of
vapor is more for higher volume fraction offiller and larger grain size of conducting particles.
This paper describes the effect of electromechanical phase on electrical resistivity of a composite
consisting of magnetostrictive phase, conductive phase and insulating phase. It is found that the
resistance of three-phase composite increases with increase of applied magnetic field beyond a certain
va1e ot magnetic field. This resistivity vs. magnetic field characteric seems to be a novel
magnetoresistance effect, which is different from the conventional magnetoresistors. The mechanism of
resistance variation of three-phase composite with applied magnetic field is analysed, and the influence
of material parameter of the polymer matrix like elastic modulus on the resistance vs. magnetic field
characterics is discussed.
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