IBIC characterization of charge transport in CdTe:Cl

Studies of charge transport uniformity in bulk CdTe:Cl have been carried out using ion-beam-induced charge (IBIC) imaging. High resolution maps of charge collection efficiency, mobility-lifetime product (μτ), and drift mobility (μ) were measured using a scanning microbeam of 2 MeV protons focused to a beam diameter of ∼3 μm. Excellent charge transport uniformity was observed in single crystal CdTe:Cl, with electron μτ values of up to 5 × 10⁻³ cm²/V s. The presence of extended defects such as tellurium inclusions was also studied using IBIC, and their influence on the charge transport performance of CdTe detector structures is discussed. The text was submitted by the authors in English.     

离子束感生电荷显微术的研究

使用低束流技术 ,在高分辨率扫描质子微探针装置上开展了离子束感生电荷显微术 ,并研究了半导体材料 Ga As的电子学性能。实验结果表明 ,在同一扫描区域内 ,材料的电荷收集效率具有不均匀特性 ,而且氦离子激发产生的 IBIC显微图谱的对比度比质子要强。     

High-gain free electron lasers using induction linear accelerators

High-power free electron lasers (FEL's) can be realized using induction linear accelerators as the source of the electron beam. These accelerators are currently capable of producing intense currents (10²-10⁴A) at moderately high energy (1-50 MeV). Experiments using a 500 A, 3.3 MeV beam have produced 80 MW of radiation at 34.6 GHz and are in good agreement with theoretical analysis. Future experiments include a high-gain, high-efficiency FEL operating at 10.6 μm using a 50 MeV beam.     

Interface effect in pentacene field-effect transistors from high energy proton beam irradiation

We report the effect of irradiation using 10 MeV high energy proton beams on pentacene organic field-effect transistors (OFETs). The electrical characteristics of the pentacene OFETs were measured before and after proton beam irradiation with fluence (dose) conditions of 10¹², 10¹³, and 10¹⁴ cm⁻². After proton beam irradiation with fluences of 10¹² or 10¹³ cm⁻², the threshold voltage of the OFET devices shifted to the positive gate voltage direction with an increase in the current level and mobility. In contrast, for a high proton beam fluence condition of 10¹⁴ cm⁻², the threshold voltage shifted to the negative gate voltage direction with a decrease in the current level and mobility. It is evident from the electrical characteristics of the pentacene OFETs treated with a self-assembled monolayer that these experimental observations can be attributed to the trapped charges in the dielectric layer and pentacene/SiO₂ interface. Our study will enhance the understanding of the influence of high energy particles on organic field-effect transistors.     

多晶碘化汞探测器的制备及性能

碘化汞(HgI2)晶体由于原子序数高、禁带宽、密度大,制成低能γ射线和X射线探测器不需液氮冷却就能得到相当好的能量分辨率,且有相当高的探测效率.制备了多晶HgI2探测器,结果显示所得器件在室温下对5.9 keV的55Fe X射线和5.5 MeV的241Amα粒子具有较好的能量分辨率,分别为0.24 keV和0.72 MeV(未使用准直器).     

SRAM single event upset calculation and test using protons in the secondary beam in the BEPC

The protons in the secondary beam in the Beijing Electron Positron Collider(BEPC) are first analyzed and a large proportion at the energy of 50-100 MeV supply a source gap of high energy protons.In this study, the proton energy spectrum of the secondary beam was obtained and a model for calculating the proton single event upset(SEU) cross section of a static random access memory(SRAM) cell has been presented in the BEPC secondary beam proton radiation environment.The proton SEU cross section for different characteristic dimensions has been calculated.The test of SRAM SEU cross sections has been designed,and a good linear relation between SEUs in SRAM and the fluence was found,which is evidence that an SEU has taken place in the SRAM.The SEU cross sections were measured in SRAM with different dimensions.The test result shows that the SEU cross section per bit will decrease with the decrease of the characteristic dimensions of the device,while the total SEU cross section still increases upon the increase of device capacity.The test data accords with the calculation results,so the high-energy proton SEU test on the proton beam in the BEPC secondary beam could be conducted.     

Visualization of Current and Mapping of Elements in Quantum Dot Solar Cells

The delicate influence of properties such as high surface state density and organic–inorganic boundaries on the individual quantum dot electronic structure complicates pursuits toward forming quantitative models of quantum dot thin films ab initio. This report describes the application of electron beam‐induced current (EBIC) microscopy to depleted‐heterojunction colloidal quantum dot photovoltaics (DH‐CQD PVs), a technique which affords one a “map” of current production within the active layer of a PV device. The effects of QD sample size polydispersity as well as layer thickness in CQD active layers as they pertain to current production within these PVs are imaged and explained. The results from these experiments compare well with previous estimations, and confirm the ability of EBIC to function as a valuable empirical tool for the design and betterment of DH‐CQD PVs. Lastly, extensive and unexpected PbS QD penetration into the mesoporous TiO₂ layer is observed through imaging of device cross sections by energy‐dispersive X‐ray spectroscopy combined with scanning transmission electron microscopy. The possible effects of this finding are discussed and corroborated with the EBIC studies on similar devices.     

高能电子束辐照改善电力半导体器件特性研究

用12MeV电子束对普通高压晶闸管、快速晶闸管、双向晶闸管进行辐照，测试这几种器件的主要电学参数。实验发现12MeV电子辐照能明显改善这些电力半导体器件的电学性能。辐照后的器件经过退火处理，可以长期稳定工作。     

Advantages and Limits of 4H-SIC Detectors for High- and Low-Flux Radiations

Silicon carbide (SiC) detectors based on Schottky diodes were used to monitor low and high fluxes of photons and ions. An appropriate choice of the epilayer thickness and geometry of the surface Schottky contact allows the tailoring and optimizing the detector efficiency. SiC detectors with a continuous front electrode were employed to monitor alpha particles in a low-flux regime emitted by a radioactive source with high energy (>5.0 MeV) or generated in an ion implanter with sub-MeV energy. An energy resolution value of 0.5% was measured in the high energy range, while, at energy below 1.0 MeV, the resolution becomes 10%; these values are close to those measured with a traditional silicon detector. The same SiC devices were used in a high-flux regime to monitor high-energy ions, x-rays and electrons of the plasma generated by a high-intensity (10¹⁶ W/cm²) pulsed laser. Furthermore, SiC devices with an interdigit Schottky front electrode were proposed and studied to overcome the limits of the such SiC detectors in the detection of low-energy (～1.0 keV) ions and photons of the plasmas generated by a low-intensity (10¹⁰ W/cm²) pulsed laser. SiC detectors are expected to be a powerful tool for the monitoring of radioactive sources and ion beams produced by accelerators, for a complete characterization of radiations emitted from laser-generated plasmas at high and low temperatures, and for dosimetry in a radioprotection field.     

双向四电子束泵浦KrF主放大器能量沉积

用三维电子输运Ｍｏｎｔｅ－Ｃａｒｌｏ（ＭＣ）方法研究了双向四电子束泵浦ＫｒＦ准分子激光器ＭＯＰＡ系统中主放大器（Ｈ１Ｍ）的能量沉积空间分布。计入了Ｈｉｂａｃｈｉ结构和主膜的影响。对０．５ＭｅＶ的电子，泵浦方向能量沉积基本均匀，而在轴向，因为两窗口间的１４ｃｍ“死区”使得能量沉积呈“马鞍形”，峰谷比为２～３。给出了能量沉积的总量及能量沉积效率与电子束能的关系曲线，为Ｍａｒｘ发生器的二极管电压进行优化设计提供了依据。     

Structural and electrical investigation of BLT films deposited at different times using electron beam evaporation technique

Thin films Bi4Ti3O12 (BLT) were deposited using electron beam evaporation on silicon substrate at several times, also on AlN/Si and SiO2/Si substrates. Thin films morphology and thickness were measured via scanning electron microscopy (SEM). The crystallography was studied using X-ray diffraction (XRD) technique for films which have a (0010) preferred orientation in all substrate types. The capacitance values were contingent on frequency value in C-V measurement. The ferroelectric characterization was investigated for BLT film deposited on isolator layer (SiO2 or AlN) for Al/Bi4Ti3O12/SiO2/Si devices. Memory effect value varied from 1 V to 3 V depending on the thin films isolator on substrate.     

Optical waveguides in fluoride lead silicate glasses fabricated by carbon ion implantation

The carbon ion implantation with energy of 4.0 MeV and a dose of 4.0×1014 ions/cm2 is employed for fabricating the optical waveguide in fluoride lead silicate glasses. The optical modes as well as the effective refractive indices are measured by the prism coupling method. The refractive index distribution in the fluoride lead silicate glass waveguide is simulated by the reflectivity calculation method (RCM). The light intensity profile and the energy losses are calculated by the ?nite-difference beam propagation method (FD-BPM) and the program of stopping and range of ions in matter (SRIM), respectively. The propagation properties indicate that the C2+ ion-implanted fluoride lead silicate glass waveguide is a candidate for fabricating optical devices.     

940 nm高功率半导体激光器研究

报道了一种采用大光学腔结构的InGaAs/GaAs/AlGaAs应变量子阱高功率半导体激光器。在量子阱能级本征值方程的数值求解基础上 ,优化了InGaAs阱层材料的In组份含量 ;采用大光学腔结构以有效降低垂直于结平面方向的光束发散角及腔面的光功率密度 ,实现器件的高功率、低发散角光。设计的激光器外延结构采用分子束外延 (MBE)方法生长 ,成功获得具有较低激射阈值的 94 0nm波长激光器外延片。对 10 0 μm条形 ,10 0 0 μm腔长的制备器件测试表明 ,器件的最大连续输出功率达到 2W ,峰值波长为 939.4nm ,远场水平发散角为 10° ,垂直发散角为 30°。器件的阈值电流为 30 0mA。     

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.     

The stimulated Cerenkov interaction and its applications

Reviewed are the results of two experiments in which momentum modulation of a relativistic electron beam by laser fields using the stimulated Cerenkov interaction was measured, and coherent Cerenkov radiation from the optically bunched electron beam was observed. In the first experiment, light at 1.06 μm from a 30 MW Nd:YAG laser intersected 102 MeV electrons at an angle of 18 mrad in hydrogen gas, which was used as the phase-matching medium. The change in the electron-beam energy spectrum in the presence of the laser was measured, together with its functional dependence on the index of refraction of the phase-matching medium. In the second experiment, the same laser intersected 55.9 MeV electrons at an angle of 17 mrad, again in hydrogen gas. Coherent Cerenkov radiation at the second harmonic of the laser frequency (0.532 μm) was measured and indicated that the electrons were bunched on the order of the laser wavelength as a result of being velocity modulated by the laser. Applications of these results, such as development of optical klystrons and laser-driven particle accelerators, are considered. The characteristics of these devices and possible design configurations are discussed.     

Self‐Assembly of Atomically Thin Chiral Copper Heterostructures Templated by Black Phosphorus

The fabrication of 2D systems for electronic devices is not straightforward, with top‐down low‐yield methods often employed leading to irregular nanostructures and lower quality devices. Here, a simple and reproducible method to trigger self‐assembly of arrays of high aspect‐ratio chiral copper heterostructures templated by the structural anisotropy in black phosphorus (BP) nanosheets is presented. Using quantitative atomic resolution aberration‐corrected scanning transmission electron microscopy imaging, in situ heating transmission electron microscopy and electron energy‐loss spectroscopy arrays of heterostructures forming at speeds exceeding 100 nm s^?1 and displaying long‐range order over micrometers are observed. The controlled instigation of the self‐assembly of the Cu heterostructures embedded in BP is achieved using conventional electron beam lithography combined with site specific placement of Cu nanoparticles. Density functional theory calculations are used to investigate the atomic structure and suggest a metallic nature of the Cu heterostructures grown in BP. The findings of this new hybrid material with unique dimensionality, chirality, and metallic nature and its triggered self‐assembly open new and exciting opportunities for next generation, self‐assembling devices.     

基于双轴锥镜的环形激光束整形

为了改善非稳腔高能激光系统的光束质量,提高发射光学系统口径的利用率,采用新型的可用于光学非稳腔输出环形光束的光学整形方法,通过在激光腔外的光路上增加光学元件对输出的环形激光束进行了整形变换。在理论分析的基础上,设计并加工了基于双轴锥镜的光束整形装置,针对非稳腔高能激光器输出的环形光束进行了整形实验,取得了与理论分析一致的数据。结果表明,采用双轴锥镜装置整形后的光束比原始光束具有更好的光束质量,光束束腰直径由45mm减小为32mm,光束质量因子M2由14减小到11.8。该方法用于光学非稳腔输出环形光束整形变换具有可行性。     

Experimental results from the Los Alamos FEL photoinjector

The authors report some initial measurements of electron beam properties from the new photoinjector installed as the front end on the Los Alamos free-electron laser (FEL). The FEL is being rebuilt with the photoinjector, added acceleration to 40 MeV, new diagnostics, and a beam line designed to minimize emittance growth. The authors measured the spatial and temporal properties of the beam at energies of about 15 MeV as a function of several parameters and the results have been compared to simulations. The operational characteristics of the important elements of the system and the theoretical comparisons are described     

Focussed ion beam and field emission gun–scanning electron microscopy for the investigation of voiding and interface phenomena in thin‐film solar cells

The use of focussed ion beam milling combined with high resolution scanning electron microscopy analysis as a characterisation tool for thin‐film photovoltaics is reported. CdTe solar cell cross sections are examined in high detail with as‐grown and CdCl₂‐treated devices being compared. Observed changes in microstructure of the thin‐film layers are related to the device performance. The CdCl₂ treatment is shown to cause a reduction in the CdTe defect density at regions close to the interface and induce recrystallization of the CdS layer. Furthermore, the focussed ion beam technique is shown to reveal voids formed within the device's thin‐film layers at various processing stages that have not been previously observed in working cell structures. The back‐contacting Te‐rich layer resulting from nitric–phosphoric acid etching is also observed, with the etched layer being seen to propagate down the CdTe grain boundaries. Copyright © 2011 John Wiley & Sons, Ltd.     

兰州高能电子成像实验研究平台进展

兰州高能电子成像实验研究平台是中国科学院近代物理研究所建造的唯一专用于高能电子成像及相关领域的实验研究平台,目前已完成第一阶段基于热阴极微波电子枪电子直线加速器的研制,电子束能量50 MeV,最大宏脉冲束流300 mA,达到了设计指标并通过技术测试.开展了高能电子成像实验,空间分辨4 μm,获得了预期结果.