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.
Uncooled terahertz (THz) focal-plane arrays (FPA) can realize real-time, continuous-wave terahertz detection and imaging. In this paper, the design method of adjustable DC bias voltage for 320×240 room temperature terahertz focal plane is introduced. The logic timing based on ASIC chip JL7603B is realized. The analog output signal of room temperature terahertz focal plane array is digitized by LTC2245 analog-to-digital converter. Data acquisition and real-time imaging are realized by interacting with the PC through the USB data cable. Using a modular design method, a compact terahertz camera core was successfully designed, the size was 25mm × 25mm × 35mm, the weight was less than 70g and the power consumption was less than 1.2W. The test results show that the signal processing and data acquisition of the terahertz focal plane through the camera core, the RMS noise is 388.6μV, the non-uniformity is 5.91% and the function of THz real-time detection is realized.
Topological insulators (TIs) are theoretically predicted to be promising candidate materials for broadband photodetection from the visible to the infrared (IR). As a 3DTI, Bi2Te3 has reattracted greater interest in recent years. Here, we report a study on a self-powered organic/inorganic photodetector based on N-type Bi2Te3 thin films and P-type pentacene heterojunction with wideband response from 450 nm to 1550 nm. In addition, the optimized responsivity reaches 14.89 A W-1 , with the corresponding eternal quantum effciency of 2840%. These excellent properties prove that the combination with low molecular weight organic matter is the future direction for the preparation of high performance photodetectors by TIs. The findings represent a fundamental form scenario for advancement of the next-generation highperformance array photodetectors and highly integrated optoelectronic products.
Photodetector that use three dimensional (3D) Dirac Semimetal have received considerable attention because Dirac Semimetal is regarded as an ideal candidate electrode material. In this work, organics is steamed by heat on Cd3As2 thin film is used in the field of photoelectric detection. Surprisingly, the photodetector shows excellent photo response properties from 405 nm to 1550 nm. The device exhibiting high photocurrent responsivity (407 mA/W) and external quantum efficiency (58.7 %) at the wavelength of 808 nm, which Ri is more than six times than pure Cd3As2 thin film devices. Most interestingly, the NIR photocurrent responsivity of this device can reach 53.1 mA/W. Overall, the broadband photodetector based on using organics and 3D Cd3As2 Dirac semimetal thin film heterojunction is proved to better performance for photoelectric application. Moreover, organics/Cd3As2 thin film heterojunction also has advantage in low cost array devices. The use of Cd3As2 thin film and organics opens up a new path for the practical application of Dirac Semimetal materials.
The family of carbon allotropes (graphene, carbon nanotube) with its rich chemistry and physics, attracts a great deal of attentions in forming novel hybrid nanostructures. However, owing to the low absorption, the performance of pristine graphene and carbon nanotube photodetectors are greatly limited. Combining low-dimensional nanomaterials into hybrid nanostructures is a promising avenue to obtain enhanced material properties and to achieve nanodevices operating with novel principles. Here we demonstrate a photodetector based on carbon nanotube/graphene doped with P3HT. A broadband photodetector (covering 405-980 nm) based on such hybrid films is fabricated with a high photoresponsivity of above 104 A/W. The results presents a potential application for efficient, low-cost, scalable vis-IR photodetection for all-carbon based photodetectors.
The structural and optical characteristics of nearly stoichiometric lithium tantalate films have been studied. The LiTaO3 films were prepared by RF magnetron sputtering method and the phase was confirmed by powder X-ray diffraction. The optical properties were obtained from optical transmittance spectroscopy in UV-vis.-NIR range. The electronic band gap structure were determined from the fundamental absorption edge in the UV region. The evolution of defect structures caused by varying composition and post-growth processing has been evaluated from the optical absorption measurements. Optical absorption studies showed that the UV absorption edge is very sensitive to the composition of LiTaO3 films. The absorption features in the UV range indicate the discrete nature of conduction band and the allowed energy levels in the forbidden gap appeared due to surface defects.
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.
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.
Focal Plane Array (FPA) detector has characteristics of low cost, operating at room temperature, compatibility with the silicon CMOS technology, and high detecting performance, therefore it becomes a hot spot in infrared (IR) or terahertz (THz) detect field recently. However, the tradition structure of micro-bolometer has the conflict of the pixel size and thermal performance. In order to improve the detecting performance of small pixel size bolometer, high fill factor and low thermal conductance design should be considered. In IR detecting, double layers structure is an efficient method to improve the absorption of micro-bolometer and reduce thermal conductance. The three-dimension model of small size micro-bolometer was built in this article. The thermal and mechanical characters of those models were simulated and optimized, and finally the double layer structure micro-bolometer was fabricated with multifarious semiconductor recipes on the readout integrated chip wafer. For THz detecting, to improve the detecting performance, different dimension THz detectors based on micro-bridge structure were designed and fabricated to get optimizing micro-bolometer parameters from the test results of membrane deformation. A nanostructured titanium thin film absorber is integrated in the micro-bridge structure of the VOx micro-bolometer to enhance the absorption of THz radiation. Continuous-wave THz detection and imaging are demonstrated with a 2.52 THz far infrared CO2 laser and fabricated 320×240 vanadium oxide micro-bolometer focal plane array with optimized cell structure. With this detecting system, THz imaging of metal concealed in wiping cloth and envelope is demonstrated.
Multilayer lithium tantalate thin films have been successfully prepared on Pt/Ti/SiO2/Si(100) substrate using sol-gel and spin-coating method. Polycrystalline perovskite films were obtained through pyrolysis at 400°C and subsequent calcination at various temperatures from 500°C to 700°C for 1h, which were optimized by means of X-ray diffraction, Raman spectroscopy and thermal analysis. The morphology on the top surface and fractured cross section of LT films was observed by a field-emission scanning electron microscope. The 300 nm thick LT film annealed at 650°C exhibited a dielectric constant of 19.8 and a loss tangent of 0.06 at10KHz.
The design of the collimator for dynamic infrared (IR) scene simulation based on the digital micro-mirror devices (DMD) is present in this paper. The collimator adopts a reimaging configuration to limit in physical size availability and cost. The aspheric lens is used in the relay optics to improve the image quality and simplify the optics configuration. The total internal reflection (TIR) prisms is located between the last surface of the optics and the DMD to fold the raypaths of the IR light source. The optics collimates the output from 1024×768 element DMD in the 8~10.3μm waveband and enables an imaging system to be tested out of 8° Field Of View (FOV). The long pupil distance of 800mm ensures the remote location seekers under the test.
Poly(vinylidene fluoride) (PVDF) is a semi-crystalline polymer, which indicates four different crystalline forms. In this paper, the preparation of nanoscale PVDF thin film was introduced in detail. Initially PVDF was dissolved in the N,N-dimethyl Formamide and acetone mixed solution (volume ratio 1:1). The PVDF films were prepared by spin coating method with different solution concentration, then were characterized by SEM, XRD and FTIR after annealed at different annealing temperatures (60 centigrade to 120 centigrade). Due to the formation of polarized β crystal phase in the annealing process, the pyroelectric coefficient p would be affected by different annealing temperatures. The thermal poling technique of PVDF was also shown in this paper. We investigated the polarization behavior of PVDF when they were subjected to different poling electric fields (from 50 V/μm to 80 V/μm) and poling temperatures (from 90 centigrade to 120 centigrade). For a long enough poling time, the polarization is only related to poling electric filed, while poling temperature affects the poling rate merely. Under the condition of PVDF thin film beforet breakdown, the strongger the poling electric filed intensity, the higher the pyroelectric coefficient is. The pyroelectric coefficient of fibricated PVDF film is 9.0×10-10C/cm2K after 80v/μm electric field intensity polarization from experiment result.
The metamaterial absorber in terahertz (THz) region, with the metal pattern layer/dielectric spacer/metal reflective layer sandwich structure, is characterized in this paper. The principle of metamaterial absorber absorbing terahertz wave was introduced firstly. The top layer of metamaterial absorber is a periodically patterned with metallic subwavelength structure, which also serves as an electric resonator. The bottom layer is a thick metal plane, which is used to reduce THz wave transmittance. The dielectric layer between two metallic layers results in magnetic resonance and the resonance depends on the thickness and dielectric constant of the dielectric layer. The absorption of metamaterial absorber to terahertz wave was simulated with CST software. The relationship between the size of the metamaterial structure and absorption frequency was analyzed with the simulation results. The results indicate that the absorption frequency is affected by the cell constant and geometric structure of top metal pattern, and absorption rate is related to both the thickness of dielectric layer and the size of resonator. In the end, the possibility of integrating the metamaterial absorber with micro-bridge structure to design room temperature terahertz detector was discussed, and the manufacturing process was introduced about room temperature terahertz detector with high THz wave absorption rate.
Patterning of AlCu alloy thin films is a key technology in MEMS fabrication. In this paper, reactive ion etching (RIE)
process of Al-1%Cu films was described using BCl3 and Cl2 as etching gases and N2 and CH4 as neutral gases. A four-step
process was presented to meet the etching requirements using BCl3, Cl2, N2 and CF4 as process gases. Optical emission
spectroscopy (OES) was used to monitor the state of the plasma in real time. The etching endpoint was detected by
detecting the spectral intensity change in the wavelength range of 395 ~ 400nm.
In order to increase the fill factor of small size micro-bolometer, double layer micro-bolometer was designed in this
paper with bottom sensitive/ top absorber structure. The deformation and residual stress characters of single layer and
double layer structure models were simulated and optimized, and with the optimized results, double layer structure
micro-bolometer was fabricated with multifarious semiconductor recipes. The surface image and deformation
information of the fabricated micro-bolometer was tested. By using double layer structure, the area of membrane
increases by a factor of 1.99 and 3.6 for the “L” shape leg structure and long “S” shape structure, respectively.