Development of terahertz mixers and a study of their characteristics

We develop terahertz mixers with monolithic integrated circuits containing balanced, series and antiparallel pairs of Schottky diodes. The designs of these mixers and a method for studying their parameters are described. The best results are obtained for the antiparallel diode pair. In this case, the double-sideband noise temperature of the receiver amounts to 5600–7500 K when operating at the second heterodyne-oscillator harmonic near the frequency 0.71 THz.     

Semiconducting superlattice as a solid-state terahertz local oscillator for NbN hot-electron bolometer mixers

We present the results of our studies of the semiconducting superlattice (SSL) frequency multiplier and its application as part of the solid state local oscillator (LO) in the terahertz heterodyne receiver based on a NbN hot-electron bolometer (HEB) mixer. We show that the SSL output power level increases as the ambient temperature is lowered to 4.2 K, the standard HEB operation temperature.     

Noise temperature distribution of superconducting hot electron bolometer mixers

We report on the investigation of optimal bias region of a wide-band superconducting hot electron bolometer(HEB)mixer in terms of noise temperature performance for multi-pixel heterodyne receiver application in the 5-meter Dome A Terahertz Explorer(DATE5) telescope. By evaluating the double sideband(DSB) receiver noise temperature(Trec) across a wide frequency range from 0.2 THz to 1.34 THz and with a large number of bias points, a broad optimal bias region has been observed, illustrating a good bias applicability for multipixel application since the performance of the HEB mixer is uniquely determined by each bias point. The noise temperature of the HEB mixer has been analyzed by calibrating the noise contribution of all RF components, whose transmissions have been measured by a time-domain spectroscopy. The corrected noise temperature distribution shows a frequency independence relation. The dependence of the optimal bias region on the bath temperature of the HEB mixer has also been investigated, the bath temperature has limited effect on the lowest receiver noise temperature until 7 K, however the optimal bias region deteriorates obviously with increasing bath temperature.     

太赫兹雷达技术研究进展

文章介绍了太赫兹技术的发展和研究现状,概述了太赫兹波的主要特性,着重论述并举例分析了太赫兹波在雷达探测系统中的应用。太赫兹雷达具有优越的反隐形能力,很高的距离分辨率,超大信号带宽,较强环境适应能力,低截获率,强抗干扰性和穿透等离子体能力等诸多优点,在军事上有很强的应用前景,对国防和国家安全具有重要的应用价值。     

太赫兹科学与技术研究回顾

太赫兹光谱系统利用远红外辐射获得分子的某些光谱信息，这些信息在电磁谱的其他波段中是很难得到的．材料的研究是现代太赫兹系统中的重要的组成部分，一方面因为新的、大功率的太赫兹光源极大地依赖于如量子级联结构一类的新材料；另一方面，太赫兹的光谱和成像技术也为扩展诸如半导体和生物有机分子等材料的应用提供了一个有力的工具．     

太赫兹波通信技术研究进展

太赫兹波段位于红外和微波之间,在空间通信、近程战术通信等国防领域有巨大的应用前景。总结了太赫兹通信技术的特点、类别、方案及太赫兹波通信系统涉及的关键技术。介绍了近几年国内外太赫兹通信技术研究现状及取得的成果,在0.14 THz频段通信距离达到20 km,0.3 THz处通信传输速率高达105 Gb/s。分析了全电子学方法、光电子方法、量子级联激光通信等几种通信技术路线,并比较了各系统的优缺点。展望了太赫兹通信技术的发展趋势和应用前景。     

太赫兹源场致发射电子源

通过粒子模拟(PIC)软件模拟计算了在ps级别下二极与三极结构碳纳米管场致发射的电流密度与电子注聚焦性能。阳极电压在2 kV时,二极结构下电流密度达到1.85 A/cm2;三极结构下,栅压700 V时发射电流密度达到2.3 A/cm2,且在一定的三极结构参数与电极电压下,可以获得较好的电子注聚束效果。通过碳纳米管二极管发射实验,获得了6.6 A/cm2的发射电流密度,总发射电流达到52.1 mA,可以为太赫兹器件提供连续发射的电子注。     

太赫兹源场致发射电子源

通过粒子模拟(PIC)软件模拟计算了在ps级别下二极与三极结构碳纳米管场致发射的电流密度与电子注聚焦性能。阳极电压在2 kV时,二极结构下电流密度达到1.85 A/cm2;三极结构下,栅压700 V时发射电流密度达到2.3 A/cm2,且在一定的三极结构参数与电极电压下,可以获得较好的电子注聚束效果。通过碳纳米管二极管发射实验,获得了6.6 A/cm2的发射电流密度,总发射电流达到52.1 mA,可以为太赫兹器件提供连续发射的电子注。     

Tailored terahertz pulses from a laser-modulated electron beam

We present a new method to generate steady and tunable, coherent, broadband terahertz radiation from a relativistic electron beam modulated by a femtosecond laser. We have demonstrated this in the electron storage ring at the Advanced Light Source. Interaction of an electron beam with a femtosecond laser pulse copropagating through a wiggler modulates the electron energies within a short slice of the electron bunch with about the same duration of the laser pulse. The bunch develops a longitudinal density perturbation due to the dispersion of electron trajectories, and the resulting hole emits short pulses of temporally and spatially coherent terahertz pulses synchronized to the laser. We present measurements of the intensity and spectra of these pulses. This technique allows tremendous flexibility in shaping the terahertz pulse by appropriate modulation of the laser pulse.     

基于电子散热新技术的研究

随着微电子技术向小型化集成化及高频高速方向发展,热流密度急剧增加,电子散热问题己成为制约微电子工业发展的瓶颈。而传统的冷却方式不能满足其散热要求,促进人们研究和发展新的散热方式。文中就几种新型的散热技术如微通道冷却、微射流冷却、微热管冷却的研究现状、存在的问题及今后的研究方向进行综述。     

Two-dimensional electron gas characteristics of InP-based high electron mobility transistor terahertz detector

The samples of In_xGa_(1-x)As/In_(0.52)Al_(0.48)As two-dimensional electron gas(2DEG)are grown by molecular beam epitaxy(MBE).In the sample preparation process,the In content and spacer layer thickness are changed and two kinds of methods,i.e.,contrast body doping andδ-doping are used.The samples are analyzed by the Hall measurements at 300 Kand 77 K.The In_xGa_(1-x)As/In_(0.52)Al_(0.48)As 2DEG channel structures with mobilities as high as 10289 cm~2/V·s(300 K)and42040 cm~2/V·s(77 K)are obtained,and the values of carrier concentration(Nc)are 3.465×10~(12)/cm~2and 2.502×10~(12)/cm~2,respectively.The THz response rates of In P-based high electron mobility transistor(HEMT)structures with different gate lengths at 300 K and 77 K temperatures are calculated based on the shallow water wave instability theory.The results provide a reference for the research and preparation of In P-based HEMT THz detectors.     

频率步进太赫兹脉冲成像技术研究

针对太赫兹频段具有大带宽的特点,阐述了太赫兹波段进行高分辨力成像的原理,按照微波上变频的方法,将微波源通过混频和倍频方式得到太赫兹频率源;采用频率步进脉冲体制,设计和实现了220 GHz太赫兹主动成像系统;并在暗室和外场进行了分辨力测试和拉距实验,获得的纵向分辨力达4 cm,测试距离达10 m。     

Hot electrons in indium nitride: a new numerical approach to solving the electron transport problem

The electron transport in indium nitride in a heating electric field has been calculated. The results obtained are in good agreement with the known experimental data. The Boltzmann transport equation in the isotropic spatially homogeneous case has been solved using a new numerical approach based on the approximation of the distribution function from the points of a relatively thin grid in momentum space and the iterative search for a stationary solution.     

太赫兹技术在爆炸物检测中的应用

研究了太赫兹成像技术在爆炸物探测中的应用,分析了太赫兹透射型时域光谱系统的实验装置,介绍了太赫兹时域光谱的测量步骤。确定了四种爆炸物样品(TNT,RDX,DNT,HMX)在太赫兹波段的吸收谱。结果表明,这四种爆炸物样品在0~2.5THz的频率范围内均存在特征吸收峰,这为太赫兹技术检测爆炸物提供了一种有效的途径。     

频率步进太赫兹脉冲成像技术研究

针对太赫兹频段具有大带宽的特点,阐述了太赫兹波段进行高分辨力成像的原理,按照微波上变频的方法,将微波源通过混频和倍频方式得到太赫兹频率源;采用频率步进脉冲体制,设计和实现了220 GHz太赫兹主动成像系统;并在暗室和外场进行了分辨力测试和拉距实验,获得的纵向分辨力达4 cm,测试距离达10 m。     

Hot electron diffusion in CdTe

The longitudinal diffusion coefficient of electrons in CdTe has been measured with the time-of-flight technique at 300 K for field strength ranging from Ohmic values up to 60 kV/cm. The diffusion coefficient increases with increasing fields up to a maximum of 100 cm²/sec at E ≈ 15 kV/cm, that is at the threshold field for negative differential mobility, and then decreases. This behaviour, typical of Gunn effect materials, is in agreement with theoretical calculations and it is due to a first increase of electron mean energy followed by a dominant decrease of mobility.     

Hot electron diffusivity in silicon

Hot electron diffusion coefficients in silicon at room temperature are theoretically studied by incorporating the band non-parabolicity and the effect of the diffusion current on the distribution function. Two models of intervalley scattering are considered: in one model, coupling with high-temperature intervalley phonons only is assumed; in the other, low-temperature intervalley phonons are also included. Both the models give practically identical results and the calculated values are found to agree closely with the experiment.     

Hot electron diffusion in CdTe

The parallel and transverse components of diffusion constants of electrons in CdTe have been computed for fields of 30, 40, and 50 kV/cm using the Monte Carlo method. Results are presented for the velocity autocorrelation function and for the ac diffusion constants for two models of energy band structure and scattering constants, used earlier in the literature. The diffusion constants as obtained from the two models are significantly different, but none are in agreement with the available experimental results.