Synthesis,field emission and optical properties of ZnSe nanobelts,nanorods and nanocones by hydrothermal method

ZnSe nanostructures, such as nanobelts, nanorods and nanocones, were successfully synthesized on Zn foils via a hydrothermal method using EDTA as soft template at low temperature. EDTA played a significant role on the morphology of ZnSe nanomaterials. X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM) and energy dispersive spectrometer (EDS) were carried out to characterize the microstructures and chemical compositions of the as-synthesized ZnSe samples. XRD patterns indicated that the as-synthesized ZnSe samples belonged to a cubic zinc blende structure. SEM observation obviously showed that the nanocones had very sharp tips compared to nanorods and nanobelts. The field emission (FE) measurement showed that the as-synthesized ZnSe nanocones had a lower turn-on field of ~1.6 V μm⁻¹ at the current density of 10 μA cm⁻². A high field enhancement factor of ~4514 was achieved for the ZnSe nanocones. The superior field emission properties were probably attributed to the sharp tips of the ZnSe nanocones. Room temperature photoluminescence (PL) spectroscopy of the ZnSe nanostructures showed a wide band emission from blue light to orange light. The as-prepared ZnSe nanomaterials have promising applications in optoelectronic devices. A possible formation mechanism of ZnSe nanobelts, nanorods and nanocones was also proposed and discussed.     

A decoder-driver system for magnetic-core memories using a 64-position switch tube

This paper describes the design, construction, and operation of a driver-decoder subsystem using a novel 64-position switch tube. The system is designed as part of a 10 Mc/s magnetic-core memory. The switch tube is a type of cathode-ray tube (CRT) using as a target, a 64-position matrix of silicon diodes. A split-plate electrostatic deflection system is used to select one diode out of the matrix, and turn it on with the electron beam. The effect of the beam is to produce a 1.5 ampere, 150 volt, 3 ns rise time pulse. The delay through the system is 25 ns.     

一种采用厚膜混合工艺的10位高速D/A转换器

介绍了一种采用厚膜混合集成工艺制作的倒R-2R电阻网络结构的高速10位D/A转换器电路.重点分析了二极管电流开关对输出电流建立时间的影响,提出了一种改进型二极管电流开关结构,减少了二极管电流开关中电荷泄放引起的过冲,使电流建立时间大大减小,样品电路测试典型值为25 ns.     

The effect of high energy electrons during the growth of ZnSe and ZnMgSe by molecular beam epitaxy

Electron irradiation during reflection high-energy electron diffraction is shown to affect the growth of ZnSe and ZnMgSe by molecular beam epitaxy. The high-energy electrons produce an electron stimulated desorption effect during growth of ZnSe which primarily affects adsorbed Se. Se desorption rates under electron irradiation are shown to be significantly larger than thermal desorption rates. Electron irradiation also decreases ZnSe growth rates under Zn-rich conditions. The decrease in growth rate can be suppressed by either growth under Se-rich conditions or by using high-index substrate orientations, in this case (211)B. High-energy electron irradiation does not alter composition during the growth of ZnMgSe.     

汽相外延ZnSe单晶的激光发射(英文)

Much work has been done on the laser emission from ZnSe under electron beam pumping. In this paper, the stimulated emission from ZnSe epilayer has been investigated under a nitrogen laser excitation. The ZnSe epilayers were grown by vapor phase epitaxy on (100) GaAs substrates. Optically pumped lasers were fabricated from the ZnSe epilayers by cleaving the ZnSe/GaAs along the (100) cleavage planes into rectangles with widths 100-600μm, and found to operate in the blue portion of the visible spectrum at 77K. The threshold of laser emission was determined to be about 1MW/cm2 from the dependence of the total light output on excitation intensity. The exciton-exciton inelastic collision process is the dominant laser emission mechanism in the ZnSe laser at 77K.     

Surface treatment of znse substrate and homoepitaxy of znse

High quality ZnSe(100) substrates have been used for homoepitaxial growth by molecular beam epitaxy. A chemical pretreatment suitable for ZnSe substrate preparation is determined from x-ray photoemission spectroscopy studies. Thermal cleaning processes for the ZnSe(100) surface were investigated by insitu reflection high energy electron diffraction and the surface phase diagram for ZnSe(100) was obtained for the first time. The low temperature photoluminescence spectra recorded from homoepitaxial layers exhibit unsplit free and bound exciton transitions with strong intensities. The full widths at half maximum of the (400) x-ray diffraction spectra for ZnSe homoepitaxial layer were 17≈31 arcsec.     

Preparation of ZnSe light-emitting diodes by metalorganic chemical vapor deposition using trisdimethylaminoarsine as a p-type doping source

Trisdimethylaminoarsine was used in atmospheric-pressure metalorganic chemical vapor deposition growth of ZnSe on GaAs. The metalorganic precursors employed for ZnSe growth were diethylzinc and diethylselenide, and ethyliodide was used as then-type dopant. P-on-n light emitting diode (LED) structures were prepared, and molecular beam epitaxially deposited HgTe layers were used as ohmic contacts to the p-type ZnSe. Blue LEDs were fabricated on p-on-n samples. Preliminary LED data and the material characterization data are presented.     

分子束外延ZnSe/ZnSxSe1-x超晶格光学特性

用分子束外延方法在GaAs(100)衬底上生长了高质量的ZnSe/ZnSxSe1-x(x=0.12)超晶格结构，通过X射线衍射谱和光致发光谱，对其结构特性和光学特性进行了研究。结果表明：在4．4K温度下，超晶格样品显示较强的蓝光发射，主发光峰对应于阱层ZnSe的基态电子到重空穴基态的自由激子跃迁，而且其峰位相对于ZnSe薄膜的自由激子峰有明显蓝移。从理论上分析计算了由变就和量子限制效应引起的自由激妇峰位移动，理论和实验结果相吻合。     

偏振分光膜中节瘤的激光损伤特性

研究了1 064 nm HfO2/SiO2偏振分光膜中节瘤的损伤特性。为了研究偏振分光膜中节瘤缺陷种子源粒径大小与损伤阈值之间的关系,在熔石英基板上植入了尺寸和密度可控的单分散性的SiO2小球,并采用电子束蒸发技术在熔石英基板上制备了1 064 nm HfO2/SiO2偏振分光膜。为了便于损伤测试,节瘤缺陷密度控制在20~40 mm2左右,并采取旋涂的措施防止了SiO2小球团聚的现象。为了获得人工节瘤损伤能量的统计值,用脉宽为10 ns的1 064 nm脉冲激光进行了光栅扫描式损伤测试。实验结果表明在偏振分光膜中节瘤缺陷的损伤阈值随着种子源粒径的增大而单调下降。     

Selective doping of N-type ZnSe layers with chlorine grown by molecular beam epitaxy

N-type ZnSe with electron concentration up to 3 × 10²⁰ cm⁻³ and low resistivity down to 1 × 10⁻⁴ ohm-cm, has been grown using a selective doping technique with chlorine during molecular beam epitaxy. The photoluminescence evaluation shows that the selectively doped ZnSe layers are superior to uniformly doped ones, especially for the case of high-concentration chlorine doping. The in-depth profile of chlorine concentration in a selectively doped sample was measured with secondary-ion mass spectroscopy (SIMS). The SIMS analysis shows only slight diffusion of the incorporated chlorine atoms even in highly doped samples.     

分子束外延ZnSe/ZnS_xSe_(1-x)超晶格光学特性

用分子束外延方法在 Ga As(10 0 )衬底上生长了高质量的 Zn Se/ Zn Sx Se1 - x(x=0 .12 )超晶格结构 ,通过 X射线衍射谱和光致发光谱 ,对其结构特性和光学特性进行了研究 .结果表明 :在 4 .4 K温度下 ,超晶格样品显示较强的蓝光发射 ,主发光峰对应于阱层 Zn Se的基态电子到重空穴基态的自由激子跃迁 ,而且其峰位相对于 Zn Se薄膜的自由激子峰有明显蓝移 .从理论上分析计算了由应变和量子限制效应引起的自由激子峰位移动 ,理论和实验结果相吻合     

Characteristics of deep levels in Al-doped ZnSe grown by molecular beam epitaxy

We investigated the characteristics of deep levels in heavily Al-doped ZnSe layers grown by molecular beam epitaxy, whose electron concentration is saturated. Low-temperature photoluminescence showed deep level emission around 2.25 eV, and its intensity increases with Al concentration. This deep-level is located at 0.55 eV above valence band maximum, implying a point defect such as a self-activated center, Al_ZnV_Zn. Deep-level transient spectroscopy was used to investigate non-radiative trap centers in Al-doped ZnSe layers, and showed the presence of two electron trap centers at depths of 0.16 and 0.80 eV below conduction band minimum, with the electron capture cross-sections of 810⁻¹² and 1×10⁻⁷ cm², respectively. It is suggested the carrier compensation in heavily Al-doped ZnSe layers be ascribed to the deep levels.     

Nitride based high power devices: design and fabrication issues

We have modeled the breakdown voltage, critical current density and maximum operating frequency of several nitride based high power and high temperature electronic devices. It is found that the minority carrier recombination lifetime and the critical field for electric breakdown are important model parameters which influence device design and performance. Planar geometry GaN Schottky devices were fabricated and used to experimentally estimate these important parameters. Current–voltage measurements have indicated the importance of the non-planar geometries for achieving large breakdown voltages. The minority carrier (hole) diffusion length and recombination lifetime have been measured using the electron beam induced current technique. The measured hole lifetime of 7 ns and estimate for the critical field indicate the possibility of AlGaN based thyristor switch devices operating at 5 kV with current densities up to 200 A/cm² and at frequency above 2 MHz. The GaN structural and optical material quality as well as processing requirements for etching are also discussed.     

四路并联光电开关输出电脉冲性能研究

采用波长为1064 nm的ns脉冲激光器作为触发光源,利用光纤分束同时触发四路并联GaAs光电开关.得到能够得到稳定的电脉冲,任意两路电脉冲的同步精度为48ps,满足实际应用指标.     

An electron beam activated switch and associated memory

A new type of electron beam activated switch (EBAS) is described which utilizes electron beam induced charge storage in the metal-oxide-semiconductor (MOS) system. The state of the EBAS is determined by monitoring the surface conductance of the semiconductor. After discussing the basic charge-storage phenomena, memory arrays that use the electron beam for storing and reading information are described. A matrix array of EBASs in which information is stored using the electron beam and read by row-column access circuits is discussed in detail. The time to store a bit of information is a function of the current density of the electron beam; an approximate dosage of 10^-5C/cm²is required for storage. A memory design using Schlesinger's microspot tube for the electron optics is discussed. It is shown that storage of 1.0 × 10⁷bits per tube should be possible with presently available electron optical design and semiconductor technology.     

A novel Smith-Purcell free electron laser

An experiment on a novel Smith–Purcell free electron laser (FEL) is described in this paper. The FEL is driven by a relativistic sheet electron beam of middle energy. The high frequency system of the device is a quasi-optical resonator composed of a diffraction grating and a three-mirror reflector. Coherent radiation with a peak power of tens of kW at the 3 mm waveband is sucessfully detected from an experimental facility. The main experimental parameters are: sheet beam energy from 400 kV to 500 kV; pulse length of voltage 70 ns; pulse beam current 0.2 kA; synchronous guide magnetic field up to 1.2 T with 10 ms pulse length; and grating period 2.2 mm.     

低磁场S波段相对论返波振荡器模拟与实验

为实现高功率微波(HPM)系统的小型化,设计一个S波段较低磁场相对论返波管(RBWO)振荡器.针对低磁场特点,分析慢波结构、引导磁场、束压、束流等对输出微波的影响,通过模拟软件(PIC)优化结构.以此设计引导磁场为0.24 T,电子束束压为725 kV,束流为6 kA,频率为3.53 GHz,输出微波功率为1.22 G...     

A buried-cap planar stripe (BCP) GaAlAs laser with ZnSe current-confinement region by MBE

A GaAlAs visible laser with a novel structure, called a buried-cap planar (BCP) stripe laser, has been developed. It has an epitaxial ZnSe semiinsulating layer grown by molecular beam epitaxy (MBE) on a cladding layer, leaving a narrow stripe for the current confinement. In this laser a reflective index waveguide is constructed by using a channeled substrate, and the current flow is confined by growing the semi-insulating ZnSe single crystal on the cladding layer after mesa etching the cap layer. There are many advantages in this structure: the diffusion process is not necessary, the current confinement is complete, and the thermal strains and misfit dislocations can be avoided. These advantages assure a highly reliable device performance, and a high-yield fabrication process.     

Surface charging suppression using PEDOT/PSS in the fabrication of three dimensional structures on a quartz substrate

Pattern writing on insulating materials (e.g. quartz) using electron beam lithography (EBL) is a challenging task and it is even more difficult when the pattern is three dimensional (3D). Surface charging trapped on insulating substrates may deflect the electron beam during electron beam pattern writing causing undesired effects.In this work, the surface charging has been suppressed by top coating with water soluble conductive polymer layer using poly (3,4-Etylenedioxythiophene)/poly(styrenesulfonate) (PEDOT/PSS). The 3D masking profiles are created on a negative tone photoresist (Microresist, ma-N2403) using Raith150 EBL tool with variable dose controlled beam exposure. The 3D patterns have been transferred onto the quartz substrate by single step reactive ion etching (RIE) with suitable resist to substrate selectivity.We have demonstrated the fabrication of 3D geometrical shapes such as pyramids, hemispheres, and cones with dimensions down to 300 nm using this technique without any surface charging effects.     

用光导开关产生高压、高功率超快电脉冲

基于半导体材料的光导效应,设计并制做光导开关,在偏压为4000V,负载电阻Z0为50Ω时,用脉宽为～12ns的激光脉冲辐照光导开关,得到脉宽为～16ns,峰值电压为～1.8kV,峰值功率为～65kW的电脉冲,本文并对光导开关的技术关键进行了分析。