Abstract:In this paper， monodispersed CdTe quantum dots are synthesized by soft chemical method. Meanwhile， mercury cadmium telluride （Hg_xCd_1-xTe） quantum dots with the quasi continuous visible to near-infrared spectrum are prepared by ion exchange adjusting the concentration of Hg²⁺. The variable temperature photoluminescence and self-absorption characteristics of near-infrared Hg_0.33Cd_0.67Te quantum dots are deeply analyzed. The results indicate that the fluorescence intensity of Hg_xCd_1-xTe quantum dots decreases linearly with the increase of temperature （0～100 ℃）. The spectral line broad and the peak position has a red-shift （12 nm）. The partial overlap of absorption and emission spectra of quantum dots leads to self-absorption. The increase of self-absorption results in decrease of photoluminescence intensity while the concentration of quantum dots increases.

Abstract:Metal-Insulator-Semiconductor （MIS） capacitors were fabricated on In_0.74Al_0.26As/In_0.74Ga_0.26As/In_xAl_1-xAs heterostructure multilayer semiconductor materials. SiN_x and SiN_x/Al₂O₃ bilayer were applied as insulating layer to prepare MIS capacitors respectively. High-resolution transmission electron microscopy （HRTEM） and X-ray photoelectron spectroscopy （XPS） measurements indicated that， compared with SiN_x deposited by inductively coupled plasma chemical vapor deposition （ICPCVD）， Al₂O₃ deposited by atomic layer deposition （ALD） can effectively suppresses In₂O₃ at the interface between Al₂O₃ and In_0.74Al_0.26As. According to the capacitance-voltage （C-V） measurement result of MIS capacitors， the fast interface state density （D_it） of SiN_x/Al₂O₃/In_0.74Al_0.26As was one order of magnitude lower than that of SiN_x/In_0.74Al_0.26As. Therefore， it can be concluded that Al₂O₃ deposited by ALD as a passivation film can effectively reduce the interface state density between Al₂O₃ and In_0.74Al_0.26As， thereby reducing the dark current of p-In_0.74Al_0.26As/i-In_0.76Ga_0.24As/n-In_xAl_1-xAs photodiodes.

Abstract:Blocked impurity band （BIB） detectors are the state-of-the-art choice for far infrared astronomical observation. Ge：B BIB far infrared detector has been successfully developed using near-surface processing techniques. The spectral response covers a wide range from 50 cm^-1 to 400 cm^-1. At a temperature of 3.5 K and a working voltage of 30 mV， the detector exhibits a highly competitive responsivity of 21.46 A?W^-1 and a highly competitive detectivity of 4.34×10¹⁴ cm?Hz^1/2?W^-1 at the peak response of 84.9 cm^-1. The influence of the interfacial barriers on the spectral response is investigated. A new excitation model that the carriers in the contact regions can be excited over the interfacial barriers is proposed. Moreover， a new method to enhance the relative response intensity of BIB detectors in the low wavenumber region is found.

Abstract:The industrialization of copper indium gallium selenide （Cu（In，Ga）Se₂， CIGS） solar cells has attracted worldwide attention. As a thin film solar cell with high conversion efficiency， its efficiency can be compared with that of crystalline silicon solar cell， and the highest efficiency reaches 23.35% at present. For small-area laboratory solar cells， the main research focus is to accurately control the stoichiometric ratio and efficiency of absorption layer. For industrial production， besides stoichiometric ratio and efficiency， cost， reproducibility， output and process compatibility are very important in commercial production. The research progress of different preparation processes， gradient control of absorption layer composition， post-deposition treatment of alkali metal， wide band gap cadmium-free buffer layer， transparent conductive layer and flexible substrate were reviewed. From the perspective of the efficiency of CIGS solar cells， the transfer of record-breaking high-efficiency solar cell technology in the laboratory to the average industrial production level brings obvious challenges.

Abstract:The characterizations of CdTe film deposited by molecular beam epitaxy （MBE） in-suit had been studied using atomic force microscopy （AFM） and scanning electron microscopy （SEM）.The cross-hatch pattern can be seen on the CdTe film surface. The roughness of CdTe film deposited by MBE in-suit on HgCdTe is about 1~2 nm. The minority carrier lifetime of HgCdTe passivated by CdTe in-suit is larger than the HgCdTe passivated by the CdTe deposited by E-beam evaporation after etched top 1um HgCdTe at 77 K. The I-V characteristics of MW photodiodes passivated by the CdTe in-suit are similar with the photodiodes passivated by the CdTe/ZnS films.

Abstract:Total reflection X-ray fluorescence spectroscopy （TXRF） and X-ray photo-electron spectroscopy （XPS） have been used to investigate residual impurities and oxides on polished InAs substrate surface wet cleaned by different solution combination. Metal impurities Si， K and Ca are routinely detected on the cleaned InAs surface and their concentration change with the variation of solution combination. A large quantity of particles （80 nm size） is measured on the InAs substrate surface with higher residual impurity concentration. An effective wet chemical cleaning procedure is presented to prepare InAs substrate surface with less residual impurity， small particle quantity and thin oxide layer， which are beneficial to high quality epitaxial growth.

Abstract:The control of Hg vacancy concentration in HgCdTe grown by MBE with different passivation layer structures was studied. Higher Hg vacancy concentration in HgCdTe was obtained， which provides a basis for the subsequent research and development of new focal plane devices. It was found that the change of Hg vacancy concentration in HgCdTe varies with the structure of passivation layer during thermal annealing. The change is because the existence of the passivation layer of the HgCdTe surface layer changes the equilibrium process of the original thermal annealing. At the same time， the secondary ion mass spectrometry （SIMS） test and the corresponding theoretical fitting were verified the results.

Abstract:In order to verify the reliability of the circuit， the microwave performance for InP HBTs is analyzed based on Monte-Carlo method. The larger the fluctuation range is， the higher the accuracy of extracting intrinsic parameters is required. The allowable accuracy range can be inferred from the output performance. The microwave characteristics are composed of modeled S-parameters， current gain cut-off frequency and maximum oscillation frequency. The standard deviation of Monte-Carlo numerical analysis can be derived from the uncertainty curve of the intrinsic parameters of the π-topology small signal model. The results of Monte-Carlo analysis show that the requirements for the accuracy of measurement parameters are quite different under different frequencies and bias conditions， which verifies the reliability of the circuit under different conditions.

Abstract:A suspended dual- microstrip meander-line （SDMML） slow wave structure （SWS） was proposed. It consists of a metal enclosure as well as a suspended dielectric substrate， on the upper and lower surfaces of which are two metal meander-lines. As there are two electron beam tunnels locating above and below the dielectric substrate， and the electromagnetic wave has symmetrical distribution， it is possible to use one electron beam in each tunnel to drive the electromagnetic wave for a higher output power. The high frequency characteristics and the beam-wave interaction results of the SDMML SWS have been investigated by using simulation software. The hot performances of this SWS show that for two identical sheet beams with a voltage of 2050 V and a current of 0.2 A， the SDMML SWS has a maximum gain of 26 dB at 36 GHz and 3-dB bandwidth of saturation power of 8 GHz. To verify the simulation result， a SDMML SWS is fabricated by using new fabrication methods including the magnetron sputtering electroplate and laser ablation. The measured reflection loss of the SDMML SWS is better than -10 dB. The transmission loss of the fabricated slow wave structure is analyzed and verified through simulation and experimental results.

Abstract:An oscillator above 1 THz is designed and realized using InP-based resonant tunneling diode （RTD） and an on-chip antenna with Si-lens. The RTD model was built and studied with Silvaco software. The influences of the doping concentration of emitter， the thickness of barrier layer， space layer， and well layer on the DC characteristics of the device have been analyzed. The DC measurement of the RTD shows the peak current density J_p = 359.2 kA/cm²， the valley current density J_v = 135.8 kA/cm²， and the peak-to-valley current ratio （PVCR） = 2.64. According to the measurement， the maximum RF output power and oscillation frequency （f_max） are theoretically calculated， which are 1.71 mW and 1.49 THz， respectively. The oscillator with an on-chip bow-tie antenna and RTD is packaged with Si-lens. The measurement shows the output power is 2.57 μW at an operation frequency of above 1 THz， the DC power consumption is 8.33 mW. This is the first reported oscillator of frequency above 1 THz in domestic.

Abstract:Here， we present our implementation of two-dimensional （2D） high-resolution inverse synthetic aperture radar （ISAR） imaging using a 0.22 THz stepped-frequency （SF） radar system. The system is suitable for both near- and far-field imaging with a synthesis bandwidth of 12 GHz. The radar can provide highly accurate range and cross-range results in the near field， and its ISAR image can reach centimeter-level resolution upon using a phase-compensated Back-Projection algorithm （BP algorithm）. These BP-realized results indicate that THz ISAR imaging can achieve both higher precision and finer resolution when compared to previously demonstrated range-doppler （RD） results with the same SFCW radar setup. To accelerate BP’s relatively slow image retrieval process， we employ accelerated platforms based on a graph-processing unit （GPU）. Such success should pave the way for further research on near-field high-resolution radar imaging especially at THz/sub-millimeter bands.

Abstract:In this paper， a LOG capable of operating from the 4^th to the 9^th harmonic is designed and investigated. With the assistance of the 3-D particle-in-cell simulation， the key features of the designed LOG， beam-wave interaction dynamics and high-harmonic operation regimes are studied. It is shown that by tuning the external magnetic field intensity， successive excitation of the oscillation at a number of neighboring harmonics can be achieved， corresponding to radiation frequencies between 240 GHz to 460 GHz with the maximum radiation power of 19 kW. Then， a detailed study on the competitions among the 7^th， 8^th and 9^th harmonics are conducted， providing an insight into the multi-modes， multi-harmonics behavior of the high-harmonic LOG. Following that， the methods to stabilize the beam-wave interaction and enable single mode operation at high harmonics are discussed. Additionally， the characterization of the ohmic loss power at different operation harmonics is conducted.

Abstract:Near-field optical response of WTe₂ thin films was studied by using scanning near-field optical microscopy （SNOM） ， we have observed bright fringes near the edge of the thin film sample and also a thickness dependence on optical contrast to the sample and substrate. To understand this behavior， first we obtain the dielectric function of WTe₂ at room temperature by Drude-Lorentz model via fitting the infrared radiation （IR） reflectance and conductivity spectra， then the near-field ratio of thin film sample to the diamond substrate is calculated by the Finite-dipole model. The experimental result reveals that the behavior of the sample cannot be fully described by the bulk properties. We assume that a decoupled thin layer exists on the surface of the bulk. There are two possible explanations for the observation of the near-field patterns of bright outside fringes. Firstly， a hot-spot field may be produced between the tip and the sample edge due to the enhancement of the local electric field under the IR illumination， a similar behavior has been revealed in surface-metallic black phosphorus. Another probability is that the topological edge states of top decoupled monolayer WTe₂ lead to an enhancement of the local optical conductivity. This work provides a reference from the optical research of topological materials in the future.

Abstract:This paper introduced a new dual-frequency millimeter-wave Doppler radar （YBJ-DFDR， W band 94 GHz， wavelength 3.2 mm， Ka-band 35 GHz， wavelength 8.6 mm） situated at Yangbajing in the Tibet Plateau and presented detailed analysis of the detection capability through calculations and comparisons. The analysis results show that the DFDR has a high sensitivity with -39.2 dBZ and -33 dBZ at 10 km for the W-band radar and Ka-band radar， respectively. It is shown that the radar equivalent reflectivity factor measured by Ka- and W—band radar illustrates various distribution characteristics for different cloud types. When rainfall occurs， W-band radar suffers much more attenuations by precipitation than the Ka-band radar （the difference between them reaches up to 30 dB in some cases）， further， the attenuations may cause the loss of the reflectivity of W-band radar. On the other hand， when the cloud particles are mostly ice particles， the attenuation effect significantly decreased， and W-band radar shows stronger detection ability than the Ka-band radar with higher reflectivity values. In addition， it is also found that Ka-band radar is prone to miss more cloud edge areas than the W-band radar， such as the cloud top and cloud bottom area， resulting in underestimation of the cloud top height but overestimation of the cloud bottom height. The main reason is that the cloud particles in these areas are small and number concentration is generally low， which has weak reflectivity lower than the sensitivity of the Ka-band radar.

Abstract:Combined with the spaceborne lidar active observations， an Arctic summer cloud detection model is studied here based on the data from the FY-3D/MERSI-II （FengYun-3D/Medium Resolution Spectral Imager-II）. By using probability density function analysis method and introducing loss rate to optimize the correlating thresholds， an infrared cloud detection model for the Arctic summer is developed based on the confidence levels. The validation results reveal that the cloud detection results are highly consistent with the matched spaceborne lidar observations. The high confidence levels basically represent the cloudy pixels， while the low values correspond to the clear ones. The case study shows that the cloudy pixels is 100% consistent with the pixels of the confidence level higher than 0.8. When the confidence level is lower than 0.2， 10.15% of the cloudy pixels are still misjudged as clear pixels， which are primarily single-layer clouds with the cloud top heights between 4 and 6km. This may be caused probably by the cirrus clouds， which needs further study.

Abstract:A large-scale rapid DEM mosaicking method was proposed. In this method， dense tie-points were extracted from the DEM overlap areas using a block matching strategy， and the systematic errors of plane and elevation were corrected through block adjustment. Thus， an entire DEM set was generated using the mosaicking strategy of first along-track followed by cross-track. A computing strategy was adopted to accelerate the processing speed to improve the efficiency of the entire mosaicking process. The experimental results showed that the CPU/GPU asynchronous parallel method proposed in this study improves the processing efficiency by more than 18 times that of a single CPU， and realises the seamless mosaicking of multi-stripe DEMs.

Abstract:A graphene-embedded waveguide （GEW） with improved modulation capability was proposed， which can be over 2 times larger than that of conventional graphene-on-silicon （GOS） waveguide. More importantly， it is found that the improvement of modulation capability mainly results from the enhanced electric field confinement around graphene. Based on this finding， we propose a high-efficient method to optimize the modulation capability. By using this method， the optimization work can be reduced by an order of magnitude. Our work may promote the design of graphene-based electro-optic modulator with high modulation capability.

Abstract:A scatterer-size gradient photonic crystal flat lens is proposed， which can simultaneously realize point source imaging and plane wave focusing in TM and TE polarization modes，and both imaging and focusing break through the diffraction limit in TM polarization mode，and realize sub-wavelength imaging and focusing in TE polarization mode. This flat lens can realize polarization-insensitive imaging and focusing without any additional polarization components. It is expected to be used in the design of multi-functional optical polarization-insensitive imaging and focusing devices， and can be applied to real-time biological display， high-density optical storage and microelectronic lithography， and improve the application potential of gradient PC flat lens.

Abstract:A distributed small signal equivalent circuit modeling method for InP high electron mobility transistor （HEMT） was presented. The distributed capacitance effect was considered in the adopted model， which is characterized by adding three distributed capacitances. For accurate modeling， the parasitic inductances are extracted first，considerig the errors introduced by the parasitic inductances when extracting the parasitic capacitance first. The validity of the proposed small signal modeling method has been verified with excellent agreement between the measured and modeled results up to 50 GHz for InP HEMT. In addition， the S-parameters’ modeling error is less than 4% in 2 ~ 50 GHz， which also proves the high accuracy of the proposed modeling method.