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:High indium content In0.78Ga0.22As photodetector structures have been grown on InP substrates with InxGa1-xAs or InxAl1-xAs graded buffer layers wherein x changed continuously by gas source molecular beam epitaxy. Their characteristics were investigated by atomic force microscope, x-ray diffraction, transmission electron microscopy and photoluminescence. The differences between samples with the two kinds of buffer layers were studied. Results show that moderate surface morphology can be obtained with either InxGa1-xAs or InxAl1-xAs buffer layers. Larger residual strain is present in the photodetector structure with InxGa1-xAs buffer layer. On the other hand, superior optical characteristics have been observed for the photodetector structure with InxAl1-xAs buffer layer.
Abstract:A microwave-modulated reflectance spectroscopy (MMRS) measurement system was constructed. This MMRS technique was used to identify a transition from holes in valence band to electrons in the ground subband (GS) of the two-dimensional electron system (2DES) formed in a GaAs/AlGaAs heterostructure sample. The temperature (T) dependence of the MMRS shows a blue shift of the energy gap with increasing T, while the magnetic field (B) dependence of the MMRS shows a red shift of the energy gap with increasing B. Both phenomena are attributed to the band-filling effect of holes in valence band in the GaAs/AlGaAs heterostructure. A theoretical simulation based on Kramers-Kronig relation was also presented which was similar with the experimental data.
Abstract:The dislocation movement model of HgCdTe/Si which is based on Masafumi's theory of GaAs/Si was modified and improved. Rapid thermal annealing is performed on HgCdTe/Si. The results of the experiments and the theoretical calculation agree closely. We have shown a reduction as much as one order of magnitude in the number of dislocations of CdTe/Si epilayers. The lowest etched pit density (EPD) values is 2.5?105cm-2 after 500 ℃ rapid thermal annealing for 1 min.
Abstract:The results of HgCdTe long-wavelength infrared n -on-p planar photodiode arrays passivated by molecular beam epitaxy (MBE) in-situ grown CdTe film were presented in this paper. By mercury-vacancy p-type annealing, ion-implantation window exposure, ZnS ion-implantation barrier layer deposition, B -implantation, ion-implantation barrier layer removal, ZnS dielectric film deposition, metallization and indium-bump arrays fabrication, HgCdTe long-wavelength infrared n -on-p planar photodiode arrays using in-situ CdTe passivation was achieved from a Hg1-xCdxTe film covered with a layer of MBE in-situ grown CdTe film. Zero bias dynamic resistances of HgCdTe photodiode arrays using in-situ CdTe passivation were improved 1~2 times higher than those of non-in-situ CdTe passivation processed one, and the maximum dynamic resistances near small reverse biases were even increased by a factor of 30~40. Since their current-voltage curves were all measured at 78K, it is obvious that in-situ CdTe passivation was beneficial to suppress dark current of n -on-p planar photodiode by optimizing the interface between the HgCdTe detector and CdTe passivation layer, and then to enhance the performance of long-wavelength infrared photodiode arrays operating at small reverse biases.
Abstract:Stripe nonuniformity is a very typical fixed pattern noise in line infrared focal plane arrays (IR-FPA) and uncooled staring IR-FPA. Its origination was analyzed. A stripe nonuniformity correction algorithm based on brightness constancy assumption and registration was proposed. Brightness mean-square error function was obtained according to adjacent frames. Nonuniformity correction parameters could be derived through the unique global optimum by minimizing the function. Experimental results indicate that the proposed algorithm could achieve a great convergence in several frames with low computational complexity and enhance the effective of stripe nonuniformity correction.
Abstract:The non-equilibrium carrier dynamics in HgCdTe has been studied with picosecond pump-probe measurements. The delay-time dependent differential transmission shows a negative minimum after the absorption saturation maximum, which can be attributed to an additional absorption process because of the deep levels. A rate equation formalism has been employed to model the carrier dynamics. The experimental differential transmission spectrum has been fitted very well with the calculations when two deep level relaxation time constants are introduced, implying two types of the deep levels. The variation of the relaxation time with the pump intensity has also been studied.
Abstract:ZnS thin films have been deposited on glass substrates by RF magnetron sputtering. The effect of in-situ annealing in argon atmosphere at temperatures ranging from 300℃ to 500℃ on the structural and photoluminescence properties has been investigated by x-ray diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence (PL) spectroscopy. It has been found that the annealing has little effect on the crystallinity and grain size of ZnS films, but affects the photoluminescence significantly. The PL spectra of the films annealed at lower temperatures show a multiple-peak structure, while only single luminescence peak is observed for the sample annealed at 500℃. The difference in the PL spectra may result from the variation of the defect type and density in the ZnS films aroused by different annealing temperatures.
Abstract:The InAs/GaSb superlattice were prepared by metal organic chemical vapor deposition (MOCVD) on GaSb substrate. The optimized thickness and the various growth parameters were explored as well as the importance of source flux control. The photoluminescence (PL) spectra, x-ray diffraction data (XRD) and the surface topography map showed that the superlattice can response to incident light with long wavelength of 10 μm, and has good surface morphology and epitaxial layer quality.
Abstract:The crystal size and energy resolution of CdZnTe (CZT) detectors are limited by crystal growth technology. In this paper, capacitive Frisch grid detector structure was used to reduce the leakage current and overcome the charge carriers' recombination by the geometric of unipolar charge. The electrode contact of the detector was made of Schottky contact which can further compress the weight of potential and reduce the leakage current noise. A large volume multi-element parallel detector was made by capacitive Frisch grid structure and Schottky contact electrode (In-p/CZT-AuCl3). The energy resolution of multi-element detectors is not limited to the worst energy resolution unit and the detection efficiency is 2.45 ~ 7.31 times more than that of the single unit.
Abstract:Yb3 , Er3 -codoped YF3 nanoparticles were rapidly prepared via microemulsion method at room temperature. The nanoparticles were characterized by x-ray diffraction(XRD) and scanning electron microscopy(SEM). The XRD pattern matched well with card PDF#74-911. SEM patterns indicated that the nanoparticles were spherical morphology with the average size about 32 nm. Downconversion spectrum and upconversion spectrum were investigated. It was found that the predominant emission peak of downconversion spectrum was located at 1544 nm. In the upconversion spectrum, the intensity of red emission was stronger than that of green. In this material, both the red and green emissions were due to two photon processes. Meanwhile, upconversion mechanism and process were also analyzed.
Abstract:In order to select optimal spectral width for biomedical components analysis by near-infrared (NIR) spectroscopy, starting with the characteristic wavelengths of the samples, a modeling procedure based on spectroscopy principles is presented. 348 human serum samples are collected. Cholesterol and triglyceride in human sera are analyzed as an example. According to spectroscopy principles and absorbance of 2 mm-thick sera, first overtone region is selected for analysis. Models with different spectral width are compared. For cholesterol and triglyceride models, optimal spectral width is 70nm and 100nm respectively. Root mean square error of prediction (RMSEP) and mean percent error of prediction (MPEP) are 017 mmol/L, 3.0% and 0.14mmol/L, 10.3%, respectively. The performance is comparable with the best works of other groups while the spectral width is narrower.
Abstract:New method for estimating the observation error in the shortwave infrared perpendicular water stress index was presented. The new method was implemented in the two stage data assimilation scheme. From the data assimilation experiment, it was demonstrated that the improved data assimilation scheme can fairly reveal spatial variations of surface soil moisture resulted from the spatial and the quantitative heterogeneous of vegetation. Thus the accuracy of the assimilation was further improved.
Abstract:There is a little trouble to retrieve chlorophyll-a concentration (Chl-a) through remotely-sensed imageries in turbid waters, which contains many suspended sediments largely affecting the signature of water-leaving radiance due to phytoplankton pigment. Based on the in situ measurements during the period of 2004~2010, the two-band, three-band, enhanced three-band and four-band models were, respectively, regionally parameterized for the application in Tai Lake. Then the four parameterized models were validated by the in situ data in Chao Lake, almost the same water environment as in Tai Lake. The strongest linear relationship between Chl-a and the four-band model (R2 varying in the range of 0.57 and 0.95, RMSE in the range of 2.39 and 6.74 μg/L) shows that the four-band model is the best for both the Tai Lake and the Chao Lake.
Abstract:The integral moment method was proposed to solve radiative transfer in nonlinear scattering medium. In this method, the integral term of the scattering phase function was deduced to linear combinations of radiative intensity moments. The scattering phase function was expressed as a truncated Legendre series and the highest order of radiative intensity moments was equal to the approximation order of the scattering phase function. Then, the integro-differential equation was reduced to differential equation, which is solved by integral method. Since it is not required to discretize the solid angle, the integral moment method will not suffer ray effects. The results by the present method are in good agreement with those in references and the method has a high accuracy. Furthermore, satisfied results also can be obtained even in the case of fewer computational meshes.
Abstract:Based on air-sea flux algorithm and parabolic approximation method, mathematical model for the optical propagation tracing was established. Maximum Inter-Visvion Ranges(MIVR) was evaluated, and the root cause of Mirage was analyzed. Numerical analysis and sea experimental results showed that MIVR decreases with the reduction of the temperature difference (ΔT) between the air and sea when wind speed is kept constant. Under the invariant ΔT, MIVR decreases with the increase of wind speed. The decrement of MIVR decreases with ΔT decreasing. The values of MIVR decrease linearly with the height of the sensor-target. The experiment proved that evaluation of MIVR with the model has high accuracy.
Abstract:A method on fusion of dual color mid-wave infrared (MWIR) images with weak signal is presented based on suprathreshold stochastic resonance (SSR). The weak signals of two images are enhanced by SSR respectively, and the noise of images is reduced with median filter. Then images denoised are fused by support value transform (SVT), and fusion image with more information and clear details is obtained. The experimental results show that local standard deviation, local entropy and peak signal to noise ratios of images obtained by the method proposed increase 247.7% , 45.52% , 6.71% and 6.65%, respectively. The validity of the method proposed is proved.
Abstract:A passive millimeter-wave scanning imaging method using electro-optic modulation and photonic processing is presented. In this imaging method, the millimeter-wave signal in the radiometer is transformed to optical frequency by electro-optic modulation, and processed by photonic filter and photodetector. The principle of this millimeter-wave signal photonic processing method is described, and the relationship between component parameters and signal conversion is analyzed. The noise characteristics of this processing method are discussed. A passive millimeter-wave scanning imaging system using this photonic processing method was designed, and passive millimeter-wave images acquired using this method were first presented in China. The results show that the proposed passive millimeter-wave imaging method is effective and can obtain comparable imaging quality as that of traditional millimeter-wave radiometer imaging. This passive millimeter-wave imaging method has advantages such as large bandwidth and immunity to electromagnetic interferences.
Abstract:A new adaptive bidirectional diffusion process that denoises and enhances passive millimeter wave images is designed and analyzed, which can diffuse adaptively according to the local characteristics of the image. In the flat areas of the image, it executes an isotropic diffusion to denoise. On the edges of the image, it executes a forward diffusion along the tangent direction to the isophote lines to denoise, and a backward diffusion along the normal directions to sharpen edges. Experimental results, completed with simulated image as well as actual passive millimeter-wave image at 91.5 GHz, demonstrated that it can substantially denoise and enhance passive millimeter wave images.
Abstract:A Lunar Impact Crater Model is proposed by analyzing the relationship between region of interest (ROI) and local salient features of lunar imagery according to the illumination characteristics. Based on the model, an ROI detection algorithm is proposed. SURF of the highlight region and shadow region of an impact crater are extracted at first; then the homogeneous features are merged into new ones. According to the constructive constrains of the Lunar Impact Crater Model, pairs of highlight feature and shadow feature are combined to generate the ROI. The algorithm has been put into test on Chang’e-1 and Chang’e-2 lunar imagery data, and was able to correctly detect the obvious regions of impact craters with results much better than those obtained by Itti algorithm.
Abstract:A novel method for radar emitter signal recognition based on time-frequency atom feature is presented. During training, based on the over-complete time-frequency atom dictionary, a few atoms which can separate different kinds of signals best are extracted as a set of fixed feature according to the class separability. During testing, the module of inner product between atoms and signals is used as the input feature for the fuzzy ARTMAP classifier, and the radar emitter signals can be recognized automatically. Experimental results of five kinds of typical radar emitter signals show that this method reduces the computational amount of feature extraction during testing obviously, and the input features have strong concentration within classes and large separability between classes. Our method can achieve high recognition accuracy at the SNR larger than 3 dB.
Abstract:Synthetic aperture ladar (SAL), whose carrier is laser, makes use of synthetic aperture processing to improve the resolution of images. Vibrations from the platform of SAL would have effects on the imaging quality of SAL because of the short wavelength of laser. Firstly, based on the paired-echo theory, the effects of angle vibration on the imaging quality are analyzed. Then, the amplitude and the position of the paired-echoes are deduced in detail. It was found that the vibrations would result in paired false target which cannot be eliminated by the traditional windowing method used in suppressing the side-lobes. Finally, the simulations prove the validity of the analysis. It provides theoretical foundation for analysis and design of SAL system.
Editor in chief：Jun-Hao CHU
International standard number：ISSN 1001-9014
Unified domestic issue：CN 31-1577
Domestic postal code：4-335