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.     

碱金属盐催化1,2,4-三唑与α,β-不饱和酮及二酰亚胺的氮杂Michael反应

发展了一种高效的碱金属盐催化1,2,4-三唑与α,β-不饱和酮及α,β-不饱和二酰亚胺的氮杂Michael加成反应的新方法,以中等到优异的产率得到目标产物.该方法原料易得,底物普适性好,反应条件温和,易实现克级规模的制备.产物容易转化为相应的γ-氨基醇.     

量子点单光子源的光纤耦合

半导体量子点在低温下产生谱线细锐的激子发光可制备单光子源.光纤耦合可避免低温共聚焦装置扫描定位和振动影响,是实现单光子源即插即用和组件化的关键技术.在耦合工艺上,基于微区定位标记发展出拉锥光纤与光子晶体腔或波导侧向耦合、大数值孔径锥形端面光纤与量子点样片垂直耦合等技术;然而,上述工艺需要多维度精密调节以避免柔软光纤的畸形弯曲实现对准和高效耦合.陶瓷插针或石英V槽封装的光纤无弯曲且具有大平滑端面,只要与单量子点样片对准贴合就可保证垂直收光, V槽封装的排式光纤还可通过盲对粘合避免扫描对准,耦合简单.本文在前期排式光纤粘合少对数分布Bragg反射镜(distributed Bragg reflector, DBR)微柱样片实现单光子输出基础上,经理论模拟采用多对数DBR腔提升样片垂直出光和光纤收光效率,使光纤输出单光子计数率大大提升.     

Quantum frequency down-conversion of single photons at 1552 nm from single InAs quantum dot

Near-infrared single photon sources in telecommunication bands, especially at 1550 nm, are required for long-distance quantum communication. Here a down-conversion quantum interface is implemented, where the single photons emitted from single In As quantum dot at 864 nm is down converted to 1552 nm by using a fiber-coupled periodically poled lithium niobate(PPLN) waveguide and a 1.95 μmm pump laser, and the frequency conversion efficiency is ~40%. The singlephoton purity of quantum dot emission is preserved during the down-conversion process, i.e., g~((2))(0), only 0.22 at 1552 nm.This present technique advances the Ⅲ-Ⅴ semiconductor quantum dots as a promising platform for long-distance quantum communication.     

全媒体时代新闻的创新融合

新媒体快速崛起,并以其方便快捷、海量的信息、不受时间地点限制、受众门槛低等优势吸引了大众的眼球。经过几年的发展融合,我国的传统媒体与新媒体已经进入了深度融合阶段,如今媒体的融合正在从传播渠道、平台、经营活动等方面,向全产业链条、全数字化、全运营化方向发展。笔者认为,新媒体时代下传统媒体的权威性不可替代,新闻报道应该运用多种手段融合,实现优势互补,弘扬主流价值,坚守人文情怀,使正能量的传播方式多样化,传播效果最大化。     

正交频分复用(OFDM)技术多径噪音降解

OFDM是基于多路载波的新型信号调制传输技术,相对于传统的单载波系统,虽然有效地扩展了信道容量,但多径传播各路信号难以事先关联,不可避免出现子信道信号相互干扰。如何消除各种干扰,对信号传输进行噪音降解是通信实践中的重要事项。文章依据据OFDM技术各关键技术的特点,论述噪音降解的各种手段。     

固态源分子束外延生长碳掺杂InGaAs材料研究

采用固态源分子束外延系统(SSMBE),以四溴化碳(CBr4)作为碳掺杂源,系统研究了半绝缘InP衬底上碳掺杂InGaAs材料的外延工艺.为得到高质量高浓度P型掺杂InGaAs材料,分别对外延过程中的脱膜工艺、P/As切换工艺以及生长温度等关键参数进行研究.通过扫描透射电子显微镜(STEM)测量衬底表面氧化膜厚度,量化...     

Optimization of wide band mesa-type enhanced terahertz photoconductive antenna at 1550 nm

A mesa-type enhanced InGaAs/InAlAs multilayer heterostructure(MLHS) terahertz photoconductive antenna(PCA)at 1550 nm is demonstrated on an InP substrate. The InGaAs/InAlAs superlattice multilayer heterostructures are grown and studied with different temperatures and thickness ratios of InGaAs/InAlAs. The PCAs with different gap sizes and pad sizes are fabricated and characterized. The PCAs are evaluated as THz emitters in a THz time domain spectrometer and we measure the optimized THz bandwidth in excess of 2 THz.     

分子束外延GaAs基M-HEMT与Si基HEMT材料研究北大核心

在GaAs基渐变缓冲层高迁移率晶体管(M-HEMT)器件中,二维电子气的输运性能对器件性能有决定性作用。系统研究了GaAs M-HEMT材料中不同In组分沟道和生长温度对沟道电子迁移率和薄层电子浓度的影响。结果表明,沟道In组分为0.65时,材料电学性能最好;提高生长温度能有效提高材料的迁移率。为了后续将Si CMOS技术与HEMT材料结合实现高集成度应用,将M-HEMT结构外延在硅衬底上并得到了初步的研究结果,室温下电子迁移率为3300 cm^(2)/(V·s),薄层电子浓度为4.5×10^(12)cm^(-2)。     

电能计量自动抄表技术的现状与展望

本文简要讲述了电能计量装置自动抄表技术的产生原因,分析了人工抄表的现状和自动抄表的优点,指出了计量装置自动抄表的热点问题和发展方向,并畅谈了自己的想法和见解.