Abstract:Recently, a high localized carrier extraction efficiency and increasing of absorption coefficient was observed in low-dimensional semiconductors within a PN junction. Such phenomenon provides the possibility of fabricating novel high performance quantum well interband transition detector. In this work, we report the performance of the first photon detector based on the interband transition of strained InGaAs/GaAs quantum wells. The external quantum efficiency was measured to be 31% using only 100nm effective absorption thickness without an anti-reflection layer. Such high value leads to an absorption coefficient of 3.7×104 cm-1 which is obviously larger than previously reported values. The results here demonstrate the possibility of fabricating high performance and low cost infrared photon detectors.

Abstract:The influence on the Low-defect surface of GaSb thin-film material by the ratio of Sb to Ga (V/III) along with the reducing of the growth temperature is investigated systematically. In order to obtain a good surface morphology of the GaSb epitaxial layer with low defect, both of the growth temperature and the V/III ratio should be reduced at the same time. The optimal growth conditions of Low-temperature GaSb thin films are that the growth temperature is T_c + 60°C and the V/III ratio is about 7.1, when the Sb cracker temperature is 900°C.

Abstract:The SnO2 film was successfully deposited on Si wafer by a simple chemical bath method to fabricate n-SnO2/p-Si heterojunction structure photoelectric device. The self-made chemical bath system is very cheap and convenient. The structural, optical and electrical properies of the SnO2 film were studied by XRD, SEM, XPS, PL, UV-VIS spectrophotometer and Hall effect measurement. The current-voltage (I-V) curve of SnO2/p-Si heterojunction device was tested and analyzed in detail. SnO2/p-Si heterojunction shows a prominent visible-light-driven photoelectrical performance under the low intensity light irradiation. Great photoelectric behavior was also obtained.

Abstract:Thin films of Mn-Co-Ni-O (MCNO) with different cation distribution are deposited by the magnetron sputtering method. By analyzing the material structure, it can be found that the grain size grows gradually with increasing Co ion number, while the lattice parameter grows first and then decreases when the Mn ion number is constant,. The preferentialSorientation ofSthe thin films changesSfromS(311) planeStoS(400) plane with increasing Mn ion number and the properties of the thin films are unstable when the Co ion number is constant. The electrical properties show that both of the Mn ions and the Co ions participate in the conductivity, and Mn1.2Co1.5Ni0.3O4 has the lowest resistivity (235 Ω.cm) and the highest negative temperature coefficient of resistance (NTCR) |α295| (4.7%.K-1) at room temperature.

Abstract:In this study rigorous numerical models were utilized to characterize the focal shift of the diffractive mid-infrared (MIR) silicon microlens array (MLA) with the critical size smaller than the working wavelength. We found a more pronounced focal shift in mid-infrared wavelength which is out of the range predicted by existing focal shift model. Focal properties of the MLA were also measured experimentally and shown to follow the simulation results. Our results provide a reference point in understanding the focal shift in MIR regime, which is important in terms of deciding the focal length of micro-nano lens systems, especially when dealing with the integration of diffractive devices in infrared optical system.

Abstract:In this paper, a novel antipodal Vivaldi antenna (AVA) is presented. The radiation flares are modified by a new composite compound exponential curve. A novel director containing two hybrid elliptical metal patches is proposed to improve the radiation parameters (gain, beam tilts and cross-polarization). The Measurement results show that the proposed antenna operates for 1GHz to more than 40GHz with peak gain >0dBi and >12dBi over the 15-40GHz range. The squinted beam of E-plane is less than 3° from 3 to 40GHz and less than 2° from 20 to 40GHz.

Abstract:It had been proposed that the microcavity effect could enhance the spontaneous emission rate and hence dramatically increase the modulation speed. However, the work in this paper reveals that the situation might be not completely correct for the 1.3 μm GaAs based quantum dot (QD) photonics crystal (PhC) nanolasers due to the complex carrier dynamics and closer hole levels. Based on the all-pathway rate equation model considering the carrier relaxation dynamics, the influences of quality (Q) factor of cavity on the threshold and modulation responses of 1.3-μm QD PhC nanolasers were studied. It is found that the high Q factor can improve significantly the threshold of QD PhC nanolasers, but it also increases the photon lifetime and deteriorates the modulation bandwidth. Hence there exists an optimized Q factor (~2500) for the nanolaser with a modulation bandwidth exceeding 100 GHz. For the energy consumption, the best value corresponds to a Q factor of ~ 7000. So an overall consideration is preferable in designing PhC nanocavity for both high speed and low energy consumption operation of QD lasers.

Abstract:A high performance 3 inch 0.5μm InP DHBT technology with three interconnect layers has been developed. The device epitaxial layer structure and geometry parameters were carefully studied to get the needed performance. The 0.5×5μm2 InP DHBTs demonstrated ft =350GHz, fmax=532GHz and BVCEO=4.8V, which have been modeled using Agilent-HBT large signal model. Static and dynamic frequency dividers designed and fabricated with this technology have demonstrated maximum clock frequencies of 114GHz and 170GHz, respectively. The ultra high speed 0.5μm InP DHBT technology offers a combination of ultra high speed and high breakdown voltage, makes it an ideal candidate for next generation 100GHz+ mixed signal integrated circuits.

Abstract:Spectral unmixing for hyperspectral remote sensing images is always required due to the existence of mixed pixels. However, most spectral unmixing algorithms at present are proposed based on the linear mixture model which may be invalid in many real-world scenarios with nonlinear spectral mixing effects. Therefore, nonlinear mixture models and their corresponding algorithms should be considered to improve the accuracy of endmember extraction and abundance estimation. This paper aims to introduce the recent advances in nonlinear spectral unmixing models and algorithms focusing on two main typical nonlinear mixing scenarios: intimate mineral mixtures and multilayer mixtures in vegetation covered areas. Further, data-driven nonlinear spectral unmixing algorithms such as kernel methods and manifold learning are also presented here. Finally, both advantages and defects of these models and algorithms are summarized and future research trends are analyzed.

Abstract:The dark current characteristics of long-wavelength HgCdTe were analyzed, compared upon three types of devices. By I-V measurement under different temperatures and dark current mechanisms, the dominant currents of each device were clarified at different temperatures. It is demonstrated that the B+-implanted n+-on-p planar junction on silicon substrate is comparable to that on bulk cadmium zinc telluride (CdZnTe) substrate above 80K. However, the trap-assisted tunneling current becomes dominant under 80K due to the high density of dislocations. Compared with n+-on-p junctions, the p+-on-n double-layer heterojunction inhibits the diffusion current effectively, which is good matched with the calculation result upon the parameter, derived from I-V curve fitting. This p+-on-n diode has a R0A value of 38 Ω·cm2 at 80K, for the cut-off wavelength of 9.6 μm, while that of the n+-on-p diode on bulk CdZnTe is 2.5 Ω·cm2. Below 60K, the dislocations make the R0A value of the p+-on-n diode an order of magnitude lower than that of the n+-on-p diode on CdZnTe.

Abstract:A three-dimensional tubular quantum well infrared photodetector (QWIP) was demonstrated via rolled-up technology, which was on the basis of conventional lithography and wet chemical etching. When the tubular QWIPs and the corresponding planar devices were illuminated by the vertically-incident light, their dark current, blackbody response, and photocurrent responsivity spectra were characterized. Under the operating temperature of 60 K and the bias of 0.45 V, a peak responsivity of 20.6 mA/W and a peak quantum efficiency of 2.3% at the peak response wavelength of 3.62 μm were obtained in the tubular devices. By clarifying the principle of optical absorption, the tubular QWIP presents a novel optical coupling manner. The device photocurrent responsivity spectra for the external light were further studied at different incident angles. It is shown, that as the approximate circular symmetry of the microtubes, the tubular devices have a wide perspective, which is advantageous to the design of infrared detection system.

Abstract:To solve the problem that the conventional optical time domain reflectometer (OTDR) not only required high-power laser output and long cumulative time but also exhibited low resolution, this paper proposes an OTDR with a high-speed single-photon detector based on InGaAs/InP avalanche photodiode. The working repetition frequency of this single-photon detector was 1 GHz, achieving "quasi-continuous" detection, realizing quick capture of return signal at single-photon level without scanning. Finally, with the emitting pulsed laser of 50 ps pulse width and 10 mW peak power, this OTDR whose event dead zone is less than 1 m, could obtain the longest measuring distance of 50 km with 10 cm accuracy.

Abstract:As an advanced ecological friendly semiconducting material, the researches on the preparation methods and optical properties of Mg2Si film play a fundamental role in the applications and development of Mg2Si films. Semiconducting Mg2Si films were prepared by electron beam evaporation deposition of Mg film onto Si (111) substrate and subsequent heat treatment under Ar gas atmosphere. X-ray diffraction (XRD), scanning electron microscopy (SEM) and spectrometer were used to characterize and analyze the obtained Mg2Si films. Effects of heat treatment time (3-7 h) at 500 ℃ under Ar gas pressure (200 Pa) on the formation of Mg2Si films were investigated. The XRD and SEM results show that semiconducting Mg2Si films are obtained by electron beam evaporation deposition and subsequent heat treatment at 500 ℃ for 3-7 h. 4 h is optimal heat treatment time to prepare Mg2Si films when heat treated at 500 ℃, and the compact Mg2Si film is obtained. The calculational results of infrared transmittance spectra of the Mg2Si films show that the indirect optical bandgap of the Mg2Si films is 0.9433 eV, and the direct optical bandgap is 1.158 eV. These experimental data are beneficial to the device research and development of the Mg2Si films in the preparation process and optical properties.

Abstract:As we know, it is difficult to identify connected defective elements by FPA test-bench because the response voltage of connected defective elements is basically the same as that of normal pixels. In this paper identification and orientation of connected defective elements in focal plane array (FPA) are presented. To characteristic of connected defective elements, we proposed a novel method which realizes the identification and orientation of connected defective elements by measuring the response voltage of detectors. Results show that the response voltage of detector can be divided into two sections by using the proposed method. The response voltage of connected defective elements is average of corresponding response voltage of the two sections units. The test data is analyzed by MATLAB software and the particular information of connected defective elements such as number, shape and location is shown. The connected defective elements are identified and orientated markedly by the technique. Our study presents a crucial step for testing and evaluating FPA.

Abstract:High frequency and power source is most important for terahtz technology, and multipliers is the best electronic way. This quadrupler design is only one stage to avoid impedance mismatches between multipliers. A proposed Schottky diode model improves the accuracy of design, which has considered the behaviors of current voltage (I/V), capacitance voltage (C/V), plasma resonance, and skin effect. Theoretical analysis was carried out by using harmonic balance simulations programs and three-dimensional finite element simulation tools to find the optimum embedding impedance for a given diode. Compact Suspended Microstrip Resonators (CSMRs) minimize the length/width ratio and make short idlers at the 2nd and 3rd harmonics. For experimental verification, the quadupler works at 325 GHz~351 GHz and output power is above 1mW between 334 GHz and 346 GHz, and the highest efficiency tested was above 3% with 100 mW.

Abstract:A process for LT-GaAs used as photoconductive switch in epitaxial layer transfer of on-chip THz antenna integrated device was provided. Hall indicated resistivity of the epitaxial materials gained by MBE was about 106Ω·cm. HNO3-NH4OH-H2O-C3H8O7·H2O-H2O2-HCl and wet chemical etching were used to etch epitaxial materials grown by MBE. Gained the structure that 1.5μm LT-GaAs bounded with COP after lift-off of GaAs SISI-GaAs and Al0.9Ga0.1As. AFM、SEM and high-power microscope indicated that the structure was flat and smooth after lift-off. RMS=2.28nm. EDAX indicated there wasn’t Al in this structure. It can be used to make photoconductive switch.

Abstract:With remote sensing images of IKONOS, SPOT5, and Landsat ETM+ and using the fraction vegetation covers with different spatial resolutions derived from a 1:500 topographic map as the reference map, we compared the accuracy of fraction vegetation cover extracted from the images radiometrically corrected using different models, and proposed the optimal radiometric correction model for the extraction of urban fraction vegetation cover. Through comparative analysis of the experimental results, we conclude that ICM model is the best radiometric correction model for urban fraction vegetation cover estimation. For high special resolution remote sensing image, NDVI is the best vegetation index for fraction vegetation cover estimation. While the best vegetation indices for estimating fraction vegetation cover from moderate spatial resolution images are the RVI and MSAVI. In terms of the study area, the fraction vegetation cover estimated by GI model is more accurate than by CR model.

Abstract:Abstract: Non-spherical aerosol is an important factor influencing aerosol remote sensing and climate simulation. In order to estimate the impact of non-spherical aerosol on polarized radiative transfer quantitatively, the sensitivity of radiance and polarized radiance to aerosol shape is analyzed for different particle effective radiuses, Aerosol Optical Depth (AOD) and solar zenith angles. In addition, the simulation errors due to the approximation that taking the non-spherical particles as sphere ones (called “equivalent Mie scattering errors”) are discussed. Considering the importance of fluxes for climate research, the influence of non-spherical aerosol on fluxes is analyzed as well. The simulation results show that, for radiance and polarized radiance, shape sensitivities are different at different directions, and the angular distributions of shape sensitivity coefficient are typical for specified solar zenith angles, which is helpful for the data selection of remote sensing process to avoid the influence of aerosol shape. Obvious simulation errors are caused by taking the non-spherical aerosol particles as sphere ones, especially for polarized radiance, where its maximum simulation error can reach 341.3%. The impact of shape on upwelling diffuse light at the top of atmosphere is much stronger than down-welling diffuse light at surface. The simulation error of fluxes due to spherical hypothesis becomes larger with increasing the effective radius. The up-welling fluxes tend to be underestimated by spherical hypothesis for small solar zenith angles, while the down-welling fluxes tend to be overestimated, the result is opposite for large solar zenith angles.

Abstract:An open ridged loaded folded waveguide slow-wave circuit has been proposed in this paper. By removing the metal boundary of the straight waveguide, an open structure has been formed to reduce the dispersion, while the ridge has been loaded to improve coupling impedance. Compared to the conventional structure the improved circuit structure not only increases the interaction impedance significantly but also keeps the dispersion characteristics well. Especially in the high-power design the coupling impedance is nearly doubled.

Abstract:In the terahertz band, diode size can no longer be ignored compared with the wavelength, significant parasitic parameters will be introduced due to diode package, so it is very necessary to establish three-dimensional model to extract parasitic parameters. Meanwhile manual assembly becomes more difficult, circuit uncertainty will increase. A 330GHz GaAs monolithic integrated sub-harmonic mixer based on planar schottky barrier diode designed by China Electronics Technology Group Corporation-13(CETC-13) and University of Electronic Science and Technology of China(UESTC) fabricated on 12um thick suspended GaAs substrate was presented. Test results show that the minimum conversion loss is 10.4dB at 328GHz, SSB conversion loss was less than 14.7dB from 320GHz to 340GHz when the LO power is 5mW.