Editor in chief：Jun-Hao CHU
International standard number：ISSN 1001-9014
Unified domestic issue：CN 31-1577
Domestic postal code：4-335
- Most Read
- Most Cited
- Most Downloaded
Abstract:Cd1-xZnx Te films were deposited by RF magnetron sputtering from Cd0.96 Zn0.04Te crystals target at different substrate temperatures, RF powers and working pressures. After deposition, the samples were annealed in high purity air at 473 K. The films were characterized using step profilometer, UV-VIS-NIR spectrophotometer, XRD and SEM. Depending on the deposition parameters and annealing, the values of the band gap of the CZT films varied between 1.45 and 2.02 eV.
Abstract:We report on the design and evaluation of two frequency bandwidth multiplying sources with planar Schottky diodes mounted on quartz thin film circuit. Novel co-simulation approach is used. Full-wave analysis is utilized to find diode deembedding impedances with lumped port to model the nonlinear junction. The doubler circuit is divided into several matching parts for ease of design. Individual parts of the doubler are independently designed and then these parts are combined and optimized simultaneously. The exported S-parameters of the whole circuit are used for multiplying efficiency analysis. For the 150 GHz doubler, the highest measured efficiency is 7.5% at 149.2 GHz and the typical efficiency is 6.0% in 147.4～152 GHz. As for the 180 GHz doubler, the highest measured efficiency is 14.8% at 170 GHz and the typical value in 150～200 GHz is 8.0%.
Abstract:A THz generation via stimulated Raman adiabatic passage in three-level Λ system was demonstrated. The basic model and theory had been analyzed in three levels coherent with pump laser and THz generation. The application also had been mentioned in D2O molecules optically pumped by a TEA CO2 laser. It produced THz radiation at the wavelength of 385 μm. The power of the THz pulse as a function of the vapor pressure, and a maximum THz power had been obtained. It was displayed that this technology is a robustness method of THz source.
Abstract:Thin thermistor films of Mn1.56Co(0.96-x)Ni0.48CuxO4 with spinel structure were prepared on amorphous Al2O3 substrate by chemical solution deposition method at a temperature of 750 ℃ in air, which is much lower than the traditional sintered temperature of 1100 ℃. The X-ray diffraction indicates that with the increase copper content, the preferred direction of crystalline is different under the same growth condition, but these films keep spinel structure well with increased crystallinity. The calculation of the grain size for all films have been performed by using the Scherrer’s equation, and we found that the grain size increased with the increase of the content of Cu.Scanning electron microscope (SEM) analysis showed that their surfaces were smooth and dense, free from cracks. The values of characteristic temperature T0, activation energy E and NTC(Negative Temperature Coefficient)α(295K) for Mn1.56Co(0.96-x)Ni0.48CuxO4 films were obtained from their electrical properties. The result revealed that a lower Cu component corresponded to a higher value of α.Increasing Cu constituent,α decreased from -4.12％ to -3.29％. The extinction coefficients of this films were determined by spectroscopic ellipsometry(SE) and their extinction coefficient peaks were identified.
Abstract:The lattice mismatched In0.68 Ga0.32 As materials were grown on InP substrate by MOCVD technology. InAsxP1-x metamorphic buffer layer structures with various As compositions were grown on InP substrates, which forms an alternative tension and strain offset buffer structure , In this way, we got a strain relaxed InAsxP1-x "virtual" substrate, which is lattice matched to In0.68 Ga0.32 As .With an optimized thickness of the buffer layer,the strain was completely relaxed in the "virtual" substrate. The analysis of AFM, HRXRD ,TEM and photoluminescence(PL) indicated that this method can effectively improve the quality of the In0.68 Ga0.32 As material.
Abstract:With the rapid development in larger-area HgCdTe infrared detector device, high-quality HgCdTe epilayers grown by molecular beam epitaxy (MBE) are required. One of its challenges is to reduce the high dislocation density in HgCdTe. In this paper, thermal annealing (TA) had been performed and the best annealing temperature and time have been acquired. A series of researches were performed to study the effects of the CdTe passivation layer over HgCdTe on dislocation reduction after thermal annealing. The relation of lattice mismatch stress and thermal stress in HgCdTe layer in the TA process was studied by theoretical calculation. Reciprocal space of X-ray rocking curve of HgCdTe was also analyzed. It explained the different phenomena of HgCdTe epilayer with and without CdTe cap in the TA process.
Abstract:The polycrystalline thin films of (Pb1-xLax)(Zr0.52Ti0.48)1-x/4O3 (PLZT) were fabricated on LNO/Si substrates by sol-gel method. X-ray diffraction showed that PLZT thin films in rhombohedral-tetragonal phase with a preferential (110) orientation can be obtained after a rapid thermal annealing process at 600 ℃. This is further confirmed by Raman spectrum. With the decrease of La content, hysteresis loops of the thin films gradually broaden. Measurement of the photovoltaic effect in the films shows that photovoltage increases gradually with the increase of the content of La from 1% to 6%. It reaches a maximum there and then decreases when the La content is increased furthermore.
Abstract:The semiconductor-passivating layer interface, as well as the dielectric properties of the passivator, plays an important role in HgCdTe based photoelectric detectors. Anodization is commonly used as a surface passivator for HgCdTe. ZnS is deposited on the AOF (anodic-oxide film) as antireflecting layer. The electrical properties of the interface between AOF/ZnS and LWIR bulk HgCdTe materials were determined by capacitance-voltage (C-V) measurements in the frequency range of 10 KHz-10 MHz in the metal insulator semiconductor (MIS) structures. The results showed that the MIS detector could not reach the high frequency level even at frequencies up to 10 MHz in the case where the interfacial state densities were 3.4×1011 cm-2q-1V-1. The fixed charges were 1.1×1012cm-2. The surface recombination velocity at the interface of AOF/ZnS and LWIR HgCdTe was 700cm/s. The variation of C-V properties with temperature has been obtained and analyzed.
Abstract:Hg1-xCdxTe (x=0.3) avalanche photodiodes (APDs) with a PIN structure was investigated theoretically. The energy dispersion factor and the threshold energy are acquired according to the parameters of material. The gain as well as the breakdown voltage of the device was obtained. The composition, thickness, doping level were optimized theoretically for the APD device. A high performance APD device with a gain of 335 at the bias voltage of-10V was fabricated, which consisted of a PIN structure mad of HgCdTe grown by MBE.
Abstract:The antilocalization effect is observed by magnetotransport measurement at low temperature on a Hg0.77Cd0.23 Te sample prepared by liquid epitaxy technique, which suggests a strong spin-orbit interaction within this system. The phase coherence time and spin-orbit scattering time of electrons are extracted by fitting the experiment data with the Hikami-Larkin-Nagaoka (HLN) theory plus the Drude conductance model. According to the temperature dependence of phase coherence time, we also find that the Nyquist mechanism dominates the dephasing process.
Abstract:In contrast to conventional band gap determination of Hg1-xCdxTe by low- temperature Fourier transform spectroscopy, we report the application of tunneling spectroscopy (STS) technique to measure the energy band gap of the vacancy-doped P-Hg1-xCdxTe grown by liquid-phase epitaxy (LPE) method. The apparent zero-current gaps measured by current-voltage tunneling spectroscopy are influenced by the imaging bias. However, the real energy band gap can be revealed by the normalized differential tunneling conductance, which were obtained using the lock-in amplifier technique. The results indicate the feasibility of room temperature band gap determination by the STS technique.
Abstract:To exploring the effect of polarity on dielectric properties of polymers, the absorption and dispersion characteristics of 5 polymers (high density polyethylene (HDPE), polyethylene terephthalate (PET), polyurethane (PU), polyvinylpyrrolidone (PVP), polyvinylidene fluoride (PVDF)) in terahertz band were studied with terahertz time-domain spectroscopy (THz-TDS). Theoretical analysis was conducted by fitting the experimental results to Debye formula. It was demonstrated from the study that dipolar polarization occurred and was enhanced with the increase of the polymer polarity, which is responsible for the increment of absorption coefficient (α), imaginary part of dielectric constant (ε") and relaxation strength (Δε). It was known that the relaxation of dipole following behind the periodical variety of THz electric field was due to the medium damping effect. As a result, abnormal dispersion behavior happened. It was found that both the refractive index (n) and the real part of dielectric constant (ε')was decreased with the increase of frequency. The relaxation time (τ) obtained from Debye fitting was also found to increase significantly with the dipole size and the rigidity of molecular.
Abstract:A method for fabricating high aspect ratio (HAR) metallic gratings using nanoimprint together with sputtering and reactive-ion etching (RIE) was introduced. The reflection spectrum is measured by Fourier transform infrared (FTIR) spectrometer in the mid-infrared (Mid-IR) region. The reflection peaks will appear just when the p-polarized light incident normally to the grating vector direction, which is very similar to the phenomenon of surface plasmon resonance. This is the so-called spoof surface plasmon resonance (SSPR). Theoretical analysis based on rigorous coupled wave showed that spoof surface plasmon resonance is very sensitive to the change of refractive index in the surface of the metal. Thus this phenomenon has its potential use as a refractive index sensor. In addition, the shift of resonance wavelength with the refractive index of the metal surface is completely linear. The refractive index sensitivity of the Mid-IR SPR sensor are predicted to be 1600 nm per refractive index unit (1600 nm/RIU) and 5000 nm/RIU for the positive and negative order diffractive waves, respectively. The corresponding figure of merits of the whole system is predicted to be 20 RIU-1 and 60 RIU-1, respectively. The list of applicable target materials will certainly expand greatly if mid-IR SPR-based sensors are developed.
Abstract:For samples with distinguishable echoes in detected transmission pulses, we mainly use the phase difference between the detected pulses to extract their refraction indices by transmission terahertz time-domain spectroscopy. Specifically, there are two methods. The first one requires the reference pulse and the first terahertz pulse transmitted through the sample; the second one requires the terahertz pulse transmitted through the sample and the second transmitted pulse after two reflections in the sample. However, in practice, there exists an angle between the incident terahertz beam and the surface normal of the sample. Yet, this angle is not easy to measure. So, in calculation we usually ignore this angle, which often causes error in the extracted refractive indices. In addition, this error is related with the selected method. In this article, after analyzing deviations of the refractive indices resulting from the angle when using the two methods, we propose a method to correct the extracting refractive indices. Our method could theoretically eliminate errors that are caused by the angle. Experiments further prove that this correction method is effective.
Abstract:The D-band MEMS rectangular waveguide iris filter was designed and fabricated. The effects of thicknesses of both metalized layer and iris, and their roughness on the performances of the filter were investigated. The prototypes were fabricated using DRIE method. Several techniques including deep etching, electroplating and bonding were employed for the fabrication of the filter. The MEMS waveguide iris filter with a central frequency of (140?3) GHz, insert loss 0.4-0.7dB, and isolation larger than 18dB has been accomplished for the first time. The test results were in agreement with the simulations.
Abstract:A novel method for random RS image simulation was proposed and realized. By integrating PROSAIL model, random classes of ground object and scale extension, random point image and random block image were simulated, respectively. In the experiment, several images, including HJ-1 CCD near infrared red spectral band image and the images with different translation, rotation and scale parameters, were quantitatively simulated. With the help of these simulated images, the effect to NIR image registration from the differences of translation, rotation and scale parameters was discussed. The action of block effect in the NIR image registration was analyzed through simulated random block images with scale diversifications and random distribution of ground object. Simulating random remote sensing images were used to analyze NIR image registration. The experimental results show that the block effect in image takes an important role to image registration.
Abstract:This paper demonstrates the designing and fabrication process of a W-wave polarizer with fine metal wires. The wires were designed to be 100 μm in diameter and 300 μm between each other. The mean values of these two parameters of the fabricated wire are 100.3 μm and 300.2 μm, with the standard deviations 5.2 μm and 8.3 μm respectively. Results show that the polarization grid has high fabrication precision and uniformity, and the polarizer surface flatness is better than 30 μm. In addition, the power transmission coefficient was measured. The actual measurement results and theoretical calculation results agree with each other perfectly. The polarizer fabricated by this new method has excellent performance.
Abstract:Aiming at enhancing the reliability of breast diffuse optical tomography, a combined time-domain diffuse fluorescence and optical tomography system is proposed based on the multi-channel time-correlated single-photon counting technique. Aligning 32 coaxial fibers around the tissue surface equally; the system scans objects in a parallel-beam mode analogous to X-ray CT so that the time-resolved projections at different incident positions can be obtained. By applying the relevant iteration reconstruction algorithm, promising images have been produced from measurements on different phantoms. The results indicate this system works reliably and is one of the ideal platforms for optical breast tumor diagnosis.
Abstract:A sort of universal theoretical analysis method for multilayer dielectric window was presented by using the mode-matching technique to build scattering matrix. The analysis of output window for high power millimeter-wave gyro-TWT was prosecuted. Based on academic analysis and numerical calculations , the primitive structure and geometric parameters of the output window had been obtained. Afterward, HFSS code is used to simulate accurately and revise approximate analysis. Through a large number of thermodynamic analysis and optimization design, the wide-band output windows of Ka-band , with average power capability 50 kW and band width about 3.6 GHz when S11 parameters less than -20 dB , were attained. The cold test indicates that the results of design are in agreement with the results of cold test.
Editor in chief：Jun-Hao CHU
International standard number：ISSN 1001-9014
Unified domestic issue：CN 31-1577
Domestic postal code：4-335