Editor in chief：Jun-Hao CHU
International standard number：ISSN 1001-9014
Unified domestic issue：CN 31-1577
Domestic postal code：4-335
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Abstract:Scaled InAlN/GaN heterostructure field-effect transistors (HFETs) on sapphire substrate with high unity current gain cut-off frequency (fT) and maximum oscillation frequency (fmax) were fabricated and characterized. In the device, scaled source-to-drain distance (Lsd) of 600 nm was realized by employing nonalloyed regrown n+-GaN Ohmic contacts. Moreover, a 60-nm T-shaped gate was fabricated by self-aligned-gate technology. A high drain saturation current density (Ids) of 1.89 A/mm @ Vgs= 1 V and a peak extrinsic transconductance (gm) of 462 mS/mm were obtained in the scaled InAlN/GaN HFETs. In addition, from the small-signal RF measurements, the values of fT and fmax for the device with 60-nm gate were extrapolated to be 170 GHz and 210 GHz at the same bias. To our knowledge, they are the highest values of fT and fmax for the domestic InAlN/GaN HFETs.
Abstract:Electronic structures and band structures of a series of InAs/GaSb superlattice in (111) orientation were calculated by density functional theory (DFT) method. Heyd-Scuseria-Ernzerhof (HSE) hybridization coupled with revised Perdew-Burke-Ernzerhof (PBE) approximation for solids and surfaces (PBEsol) showed better consistency with the experimental measurements than conventional DFT and several compared hybrid functionals. The bandgap changes with periodic thickness and InAs/GaSb ratio of InAs/GaSb superlattice. The results are in good agreement with the former experimental researches. These results indicate the feasibility of HSE coupled with PBEsol method in prediction of the electronic properties of InAs/GaSb superlattice.
Abstract:GaSb-based diode lasers with emitting wavelength of 1.8 ~ 4 μm have a wide range of applications due to advantages of compact in size, light in weight and electric drive. However, single emitter can not provide enough laser power for practical applications. Therefore, methods of beam combination which have been successfully applied to diode lasers in near-infrared band are needed to be transplanted to mid-infrared band. In every method of beam combination, high efficiency beam shaping is basic and principal. A method of high efficiency beam shaping using multiple single diode lasers was demonstrated. A continuous-wave optical power of 1.93 W at wavelength of 1.94 μm with efficiency of higher than 90% was achieved experimentally. This method of beam shaping can be utilized to build spectral or coherent beam combination.
Abstract:In this paper, an SMMW interferometric radiometer concept is demonstrated by a two-element interferometer with dedicated high accuracy SMMW devices. Point-source calibration method is introduced in order to reduce instrument errors. Interference fringes and point target images are presented by this SMMW interferometer. The linear phase error of the interference fringes is less than 2° and the angular resolution is better than 0.57°. The measured performance characteristics of the two-element interferometer are consistent with the theoretical analysis. This interferometer demonstrates a new method for passive SMMW remote sensing.
Abstract:To obtain the dark current mechanism of In0.83Ga0.17As detector, TCAD software was used to simulate its dark current property. The detectors include two structures with and without the super lattice (SL) electronic barrier in the InGaAs absorbed layer. At the same time, the detector has been fabricated to verify the simulation results. The results show that SL barrier can adjust the energy band structure and change the transport property of the carriers, and thus suppress the SRH recombination and decrease the dark current. Simulation results are in good agreement with experimental results. The influence of the location and periods of SL barrier on dark current was also simulated. The SL electronic barrier structure was optimized.
Abstract:A new method for measuring terahertz (THz) transmission spectra of bio-chemical thin films placed on the surface of a semiconductor by terahertz surface plasmon polaritons (SPPs) was proposed. A strongly confined surface plasmon in the terahertz frequency range on the surface of semiconductor was theoretically proved, which can be used to enhance the light-matter interaction with bio-chemical layers above the semiconductor surface. By employing a free-space THz time-domain spectroscopy (TDS) system, the transmission power spectra of onion epidermis films with free space transmission and SPP transmission, respectively, were experimentally obtained. Experimental results show that SPP transmission spectra represent many characteristic absorption peaks for a layer of onion epidermis film, which are more than 100 times thinner than the free space wavelength of the terahertz wave.
Abstract:GaSb-based AlGaAsSb/InGaSb type-I quantum-wells (QW) 2 μm laser diodes (LDs) have been grown by MBE system. Stripe-type waveguide LDs with facets uncoated were fabricated and characterized. For single LD device, the maximum output power was 1.058 W under continuous wave (CW) operation at working temperature of 20℃. The maximum wall plug efficiency (WPE) was 20.2% and peak wavelength was 1.977 μm with injection current 0.5 A. The output power under pulse mode of 1000 Hz in 5% duty cycles was 2.278 W.
Abstract:The spinel oxide ZnxNi1-xMn2O4 (ZNMO, x=0, 0.05, 0.1, 0.15, 0.2, 0.25) films have been grown on Pt/Ti/SiO2/Si substrate by chemical solution deposition (CSD) method. The crystallization and microstructural features of ZNMO films are studied by x-ray diffraction (XRD) and field-emission scanning electron microscopy (FESEM) analysis, respectively. The results show that the structural property of ZNMO films is affected by Zn concentration. The optical constants of ZNMO films have been analyzed by spectroscopic ellipsometry measurements in the wavelength range of 300-1 100 nm. The changes of the refractive index n and extinction coefficient k caused by Zn substituting are discussed. The A1g and F2g modes have been observed in Raman spectra. The relative intensity of the A1g mode decreases with increasing Zn concentration. The Raman peak positions shift slightly with Zn concentration x, which might result from lattice strain and lattice mismatch.
Abstract:To resolve the “false negative” and “false positive” problems in the current line segment detectors, we proposed a novel line segment detector which organizes pixels under the guidance of pixels’ gradient and improves reliability by step-by-step quality control. Before organizing pixels, initial optimized seed points were extracted according to image gradient. Under organizing, in order to solve the bad performance, e.g. noise of weak gradient, pixels were grouped and connected by considering proximity, orientation and gradient optimization to control false negative. After organizing pixels, chain division and hypothesis testing for quality control were employed to avoid false positive. When compared with state-of-the-art algorithms by visible light and color infrared (CIR) images, such as Probability Hough Transform (PHT), EDlines and LSD (Line Segment Detector), the proposed algorithm has advantages in efficiency and robustness, so it is of great significance for digital photogrammetry, computer vision and remotely sensed information extraction.
Abstract:The influence of the dip angle on light distribution inside tissue was investigated. Based on the investigation, a LOT system with condensed dip-angle (cdaLOT) over the whole detection range was developed. A new method for correcting the deflection-angle of galvanometer mirrors was also proposed. A fast image reconstruction algorithm for LOT was also developed based on the virtual-source diffusion approximation and GPU. Light path simulation showed that the developed cdaLOT system decreased the dip angle of the incident light to 1/2 of that of the traditional LOT system. The relative deviation of the measured data to MC results was about 18% for cdaLOT while that for traditional LOT was as large as 38%. Reconstructed images showed that the reconstructed absorption coefficient, and the position and shape of the inhomogeneity coincided with the real target.
Abstract:An infrared absorber based on Au/VO2 periodic square hole array is designed in this paper. The effects of structural parameters on the absorption spectrum were calculated by the finite difference time domain method. The theoretical simulation results show that the absorption tunability was the most obvious at Au film thickness of 80nm and VO2 film thickness of 140nm, and the square hole length and array period were 1.1μm and 1.2μm, respectively. The absorption difference between high and low temperature can reach to 80.3% at 2.3μm. Considering the different polarization and incident angles, it is evident that the absorber was polarization-independent at normal incidence and wide angle at oblique incidence. The angular dependence was much stronger in TE polarization compared with TM polarization. In addition, the absorber presented strong absorption because of the highly localized electromagnetic field distribution under low temperature, but the electromagnetic fields are located at the surface at high temperature, which lead to suppressed absorption. The absorber can be applied to new tunable intelligent photovoltaic device due to the advantages of high absorption efficiency, tunable absorption intensity, and easy implementation.
Abstract:A correction method in consideration both of the radiometric transfer path and BRDF effects was presented. It uses POS data to correct the change of radiation distortion caused by flight attitude. Taking the OMIS-Ⅲ data for example, results show that the spectra of the same object in the middle and edge of corrected images can match better than uncorrected ones after using the correction methods proposed above.
Abstract:LKRX detector-based hyperspectral real-time anomaly detection algorithm was proposed. Using local causal sliding array window, the causality of detection system is remained. According to Kalman filter, by using Hermitian lemma and Woodbury’s identity, the kernel covariance matrix and its inverse in KRX algorithm are updated recursively. This thereby leads to low computational complexity. Experimental results demonstrated that real-time KRX detector consumes less time in comparison with KRX detector by keeping the same detection performance, which detects more anomalies.
Abstract:Considering the motion complexity of real satellite platform and the difficulty to obtain blur kernel, a hyperspectral image blind correction method based on band selection and PSF estimation was proposed to reduce the influence of spectral redundant information on correction precision. The method combined bicubic interpolation with image deblur algorithm via directional filters. Correction experimental results show that the proposed method can compensate and correct the image motion errors introduced by various unknown satellite motion. Image sharpness is improved, and spectral distortion is also suppressed.
Abstract:A new compressive sensing(CS) sampling and reconstruction model based on spectral sparse representation is put forward in this paper. The spectral sparse dictionary is constructed from training samples to enhance the effect of sparse representation and the total variation restriction of spatial images is also considered to further enhance the precision during the reconstruction. The experiment to reconstruct 200 bands AVIRIS hyperspectral images show that the effect of spectral sparse representation enhances largely compared with traditional DCT dictionary and Haar wavelet dictionary, and the hyperspectral image is reconstructed nearly perfectly at 25% sampling rate and the spatial and spectral precision is higher than existing common methods in the same condition.
Abstract:This paper proposes an anomaly detection method based on low-rank representation and learned dictionary for hyperspectral imagery. The model of low-rank representation, which fits the linear mixing model of hyperspectral imagery more precisely compared with other low-rank decomposition algorithms such as robust principle component analysis (RPCA), was introduced to settle the anomaly detection problem for hyperspectral imagery. To improve its robustness to initialized parameters, a learned dictionary that represents only background information was adopted in the proposed method. Experiments on synthetic and real hyperspectral datasets illustrated that the proposed method is capable of improving detection results. Meanwhile, it is robust to initialized parameters and can be viewed as an effective technique to detect anomalies in hyperspectral imagery.
Abstract:Based on the closed-cavity mid-infrared laser, the temperature of the contaminant was measured when it was irradiated by a cw high energy laser with power intensity 3.16 kW/cm2. It was found that the contaminant achieves thermal equilibrium in a second and then the temperature stays at 1720 K. A physical model was established to describe the process of the thermal equilibrium. The mechanism of the mirror’s thermal damage was analyzed. It shows that the contaminant size plays an important role in the thermal damage of the optical mirror. Only when the contaminant size is smaller than a critical size (~20 μm), the contaminant may reach thermal equilibrium and the optical mirror work well in the high energy laser system. If the contaminant size is quite large (>200 μm), the optical mirror will be damaged under the irradiation of high energy laser. The results are of great help for improving the anti-damage capability of the mirror and maintaining the security of the high energy laser system.
Abstract:To improve the data quality of Ka band millimeter wave cloud radar, a quality control method for solving problems related to velocity aliasing, noisy echo, data missing and plankton contamination is presented. The effectiveness of the method was verified by several cases. The results show that the velocity dealiasing algorithm based on radar Doppler spectra processing is effective with high success rate and stability. Success rates of 15 cases reach 100%. It can also find out the fuzzy type and correct radial velocity and spectrum width. With this method, noisy clutter are filtered validly and missing data can be filling well. The plankton echoes can almost be removed clearly while the small scale cloud can be remained.
Abstract:The mathematical model of the relationship between infrared polarization angle and other parameters such as surface refractive index, reflectivity, and the detection angle was derived, based on the equation of infrared polarized radiation through micro-facet theory. Reasonable simplification for the model was made in simulation. The curve show that the polarization angle changes with the incident angle monotonously, in agree with the experimental results. It is concluded that the correlation between the polarization angle characteristics of the target edge contour and the detection wavelength can be neglected. It is difficult to distinguish between target and background by spectral radiance contrast when they have small radiation difference. While the target edge features can be obtained from the polarization angle contrast. A new method to calculate target gesture information was proposed based on geometry features of the target and the relative detection position.
Abstract:The major national strategic demands such as the global climate observation, agricultural census, land resources exploration, environmental monitoring, deep space exploration and astronomical observation are facing the bottleneck of photodetectors. Semiconductor materials and its photodetectors are rapidly developing in the direction of full-spectrum, large-array and high sensitivity, which meets the development goals of the national "strategic advanced electronic materials". In the project, low dimensional semiconductor hetero-structure photoelectric materials and devices will be investigated. Materials are going to be artificially fine-tuned to promote the technological improvements of multi-bands and multi-types of photodetectors, which is useful for the development of economy, society, national security, science and technology.
Editor in chief：Jun-Hao CHU
International standard number：ISSN 1001-9014
Unified domestic issue：CN 31-1577
Domestic postal code：4-335