Annealing of 10 MeV Electron Damage in Silicon

Annealing studies were performed to investigate the recovery of both the carrier concentration and lifetime in silicon following room temperature irradiation with 10-MeV electrons. Both n- and p-type material containing the more common dopants and varying amounts of oxygen were employed to evaluate the effect of these impurities on the annealing behavior. The recovery of carriers in n-type material was found to depend very strongly upon oxygen. A well-defined recovery stage was observed at intermediate temperature (~110° to 180° C) in oxygen-free samples but not in pulled material. The position of the stage appeared to depend upon the dopant, and for this reason it is attributed to the breakup of donor-vacancy complexes. In contrast, no appreciable carrier recovery was obtained in p-type material after anneals up to 253° C, regardless of the dopant or the oxygen content. Annealing of lifetime changes was particularly interesting. A pronounced annealing stage at ~225° C was observed in all but one of the n-type samples regardless of the oxygen content and in p-type samples containing oxygen. The detailed behavior due to this stage was dependent upon the radiation dose. Oxygen-free p-type samples exhibited completely different annealing behavior. A prominent reverse annealing stage at~144° C was observed in four of these samples and no subsequent positive recovery was observed up to 283° C.     

Model for Short-Term Annealing of Neutron Damage in p-Type Silicon

A model is presented for the short-term annealing of a damage claster resulting from neutron radiation in p-type silicon. The damage cluster is assumed to be a disordered core imbedded in an otherwise undisturbed lattice, as suggested by Gossick. The disordered core is characterized in this model by two defects. The dominant defect immediately after the damaging event is assumed to be the vacancy, which is represented by a two-level defect (donor-acceptor) in the forbidden gap. The density of this defect decreases with time as a function of the densities of its different charge states. The second defect is the divacancy which is also represented by a two-level defect in the forbidden gap. The density of the divacancies increases as the vacancies anneal. The analysis is made for a single, spherically symmetric cluster located at the center of a sphere of radius R of undamaged material. The problem is solved by the PN code which approximates the exact continuity, Poisson's, and generation-recombination equations in finite difference form. Annealing factors are obtained as a function of time by simulating a steady, uniform ionization rate throughout the sphere R. An effective lifetime for the volume R is calculated as the instantaneous average density of excess minority carriers in the sphere divided by the ionization rate. Time histories of the annealing factors are compared to experimental data obtained from shortcircuited solar cells.     

Preliminary Studies on Base Substitutions and Repair of DNA Mismatch Damage Stimulated by Low Energy N＋ Ion Beam Implantation in Escherichia coli

Ever since the low energy N+ ion beam has been accepted that the mutation effects of ionizing radiation are attributed mainly to direct or indirect damage to DNA. Evidences based on naked DNA irradiation in support of a mutation spectrum appears to be consistent, but direct proof of such results in vivo are limited. Using mutS, dam and/or dcm defective Eschericha coli imitator strains, an preliminary experimental system on induction of in vivo mutation spectra of low energy N+ ion beam has been established in this study. It was observed that the mutation rates of rifampicin resistance induced by N+ implantation were quite high, ranging from 9.2×10-8 to 4.9 ×10~5 at the dosage of 5.2 ×1014 ions/cm2. Strains all had more than 90-fold higher mutation rate than its spontaneous mutation rate determined by this method. It reveals that base substitutions involve in induction of mutation of low energy nitrogen ion beam implantation. The mutation rates of mutator strains were nearly 500-fold (GM2929), 400-fol     

Numerical Calculation of High Energy and High Current Negative Ion Beam System

In next generation large fusion devices, neutral beam injection with high energy and high power is a main tool for core plasma heating, non-induced current drive, current profile and ignition burn temperature control in high density plasma. Becase a negative ion with high energy has still higher neutral conversion efficiency, to develop the negative     

Annealing Characteristics of Neutron Irradiated Silicon Transistors

When a transistor is subjected to neutron irradiation, a component of base current proportional to neutron fluence is induced. From the effects of annealing on the base and collector currents, the conclusion was drawn that there is an apparent difference in the annealing characteristics between the neutral and the space-charge regions of the semiconductor device. This study of the anomalous annealing indicates that the neutron-induced component of base current is a result of one, or a combination, of the following mechanisms: a quasi-tunneling recombination phenomena in the emitter-base space-charge region, or an influence of the p-n junction electric field on the formation, annealing, and electronic behavior of the neutron-induced defect centers. A field dependence of the formation and annealing of the neutron-induced defects appears to be present both during the introduction and annealing of the neutron-induced defect centers. It could not be finally determined whether or not the quasitunneling phenomena occurred although it can be shown on theoretical grounds that it is possible for such phenomena to occur. The annealing characteristics of the defects, as represented by changes in the collector and base currents, have been obtained. Three sets of devices were irradiated and then annealed, with one set having a forward bias during annealing, one set having no bias, and one set having a reverse bias. The dependence of the field on annealing is present but appears quite complex.     

氦离子辐照烧结碳化硅损伤效应研究

利用中国科学院近代物理研究所320 kV高压平台提供的氦离子辐照烧结碳化硅,辐照温度从室温到1 000 ℃,辐照注量为1015~1017 cm-2。辐照完成后,进行退火处理,然后开展透射电子显微镜、拉曼光谱、纳米硬度和热导率测试。研究发现,烧结碳化硅中氦泡形核阈值注量低于单晶碳化硅。同时,氦泡形貌和尺寸与辐照温度、退火温度有关。另外,对辐照产生的晶格缺陷、元素偏析进行了研究。结果表明,辐照产生了大量的缺陷团簇,同时氦泡生长也会发射间隙子,在氦泡周围形成间隙型位错环。在晶界处,容易发生碳原子聚集。辐照导致材料先发生硬化而后发生软化,且热导率降低。     

Laser Damage of Silicon Solar Cells

Uranium-plutonium mixed monocarbide pellets, which had densities over 90% T.D. and near-stoichiometric compositions, were fabricated in the gloveboxes of the atmosphere of purified Ar. The carbide powder was first synthesized by reducing mechanically blended oxides with graphite at 1,510°C in a vacuum of 0.2 Pa. This condition was selected so as to minimize the loss of Pu during the reduction in vacuum. The synthesized carbide was milled and compacted, followed by sintering in flowing Ar at 1,540 to 1,750°C. The experimental conditions covered wide ranges of milling time, compacting pressure, sintering temperature and sintering time. The most suitable condition has been established for fabricating uranium-plutonium mixed carbide pellets by the mechanical-blend carbothermic reduction and sintering method. For the case of Ni addition as a sintering aid, the efficacy of the addition for fabricating dense pellets was confirmed, but it was noticed that the composition tended to hyperstoichiometry and the sesquicarbide phase precipitated especially at the pellet surface.     

Simulations of Cascade Damage in Silicon

In an effort to better understand radiation damage to electronic materials, we use the binary-collision simulation code MARLOWE to model displacement cascades in silicon. We examine the average number of displacements produced by knock-on atoms as a function of their energy. The resulting vacancy-interstitial pairs are classified according to separation radius. We also examine a few particular cases of 100 keV cascades in silicon in order to highlight the importance that channeling has on the shape of displacement cascades.     

低能强流氘束脉冲系统研制

为在靶上形成重复频率为4 MHz、脉冲半高宽为2 ns、平均流强为60 μA、能量为1~100 keV的氘束脉冲束,研制了1台低能氘束的脉冲化系统.系统设计中考虑了空间电荷效应,对脉冲化系统进行束流光学计算,得到了最合理的布局.通过对单漂移聚束器和切割器的计算,获得了最佳参数.针对运行于40 kV的高压平台上的特点,设计了分布式自动控制系统.设备就位后,进行了安装与调试,各设备正常运行并达到设计指标,控制系统能够方便、可靠地控制并检测高压平台上所有设备的运行情况.     

Bioeffects of Low Energy Ion Beam Implantation： DNA Damage, Mutation and Gene Transter

Low-energy ion beam implantation （10 - 200 keV） has been proved to have a wide range of biological effects and is broadly used in the breeding of crops and micro-organisms.To understand its mechanisms better and facilitate its applications, the developments in the bioeffects of low energy ion beam implantation in the past twenty years are summarized in this paper.     

Unified Model of Damage Annealing in CMOS, from Freeze-In to Transient Annealing

Irradiation studies at 76°K are described which demonstrate that radiation-produced holes in SiO2 are immobile at this temperature. If an electric field of either polarity is present in the SiO2 during 76°K irradiation, to sweep out the mobile electrons, the holes will virtually all be trapped where created and produce a uniform positive charge density in the oxide. This predicts ?VT ? dox2 , which is observed. The magnitude of the observed shift is consistent with 18 eV required per hole-electron pair generated. All CMOS transistors of the same oxide thickness exhibit the same initial ?VT, for a given exposure level, regardless of oxide type or process. The rate of annealing differs, both as a function of oxidation process and oxide thickness. Thin oxides have two advantages: a smaller ?VT (stable shift) and faster annealing. If a CMOS device is irradiated for sufficient time at 76°K to build in an appreciable field, further irradiation with zero gate-substrate bias will produce little additional change in VT, since the field in the oxide tends to keep all generated electrons in the oxide, where they recombine with trapped holes. Room temperature annealing following a pulsed gamma exposure occurs in two regimes. The first regime can be quite fast, and occurs prior to 10-4 seconds. The magnitude of this early-time recovery is both process dependent and thickness dependent.     

高温He离子辐照GH3535合金的损伤效应

采用500 keV的He离子在750 ℃下对GH3535合金样品进行辐照,然后利用掠入射X射线衍射（GIXRD）、透射电子显微镜（TEM）和纳米压痕仪分别对样品的氦泡和位错环辐照缺陷的演化及纳米硬度的变化进行了研究。结果表明,GH3535合金晶格辐照后发生了轻微畸变;离子辐照在样品中形成了大量尺寸为2～5 nm的氦泡和位错环。辐照产生的氦泡和位错环等缺陷在基体中钉扎位错,从而使材料产生了辐照硬化现象,样品硬度随辐照剂量的增加而增大。当辐照剂量达2×1016 cm-2时,辐照样品发生了明显的硬化饱和现象,利用Nix Gao模型计算得此时的硬化程度为64%。     

Calculation of Reverse Annealing in Neutron Damaged p-Type Silicon

A calculation of the reverse annealing process in neutron-burst irradiated p-type silicon at 300°K was performed, utilizing a variation of the equilibrium cluster theory of Gregory. Material conditions which were considered included 1, 10, and 100 ?-cm material with an injection ratio of 10-6 , and 1 ?-cm material with injection ratios of 10-7 and 10-8. This calculation demonstrated the relationship between the peak and time of occurrence of the damage constant versus time curve and the material resistivity and injection level. It was also shown that the reverse annealing rate depends upon the capture rate of defects in the cluster, rather than the rate of transport of defects from the depletion region to the cluster. These carrier capture rates were such that the forward annealing process usually began before the clusters reached charge saturation. Finally, it was concluded that an injected minority carrier pulse lasting less than 5×10-6 sec after burst will not appreciably affect the reverse annealing process.     

Radiation and Annealing Characteristics of Neutron Bombarded Silicon Transistors

Operating a silicon planar epitaxial transistor in the inverse configuration allows one to demonstrate clearly the importance of the neutron-induced base current component and its degradation of the emitter efficiency, and, because of the much larger depletion layer, to compute a volume dependent damage constant applicable to all silicon p-n junctions. The importance of minimizing the absolute change versus relative change in radiation hardening studies is clearly illustrated. Surface effects were found to be significant for transistors mounted in gas-filled cans. The diffusion potential was predicted, on theoretical grounds, to vary with neutron fluence, and the theory was experimentally confirmed. Isochronal and isothermal annealing data were obtained for the inverse configuration and from these data, it is concluded that the neutron-induced defect centers are field dependent.     

Injection Dependence of Transient Annealing in Neutron-Irradiated Silicon Devices

Studies have been performed to explore accurately the injection level and temperature dependence of transient annealing in neutron-irradiated P- and N-type silicon. In P-type material, the annealing factor in the 0 to 0.1 second time interval is very sensitive to the minority carrier injection level. For example, by varying the injection level from 10-5 to 10-1 the annealing factor at 0.001 second can be reduced from 10 to approximately 2. In contrast to the P-type results, the injection dependence observed in N-type silicon is very small and, furthermore, is in the opposite sense; i.e., an increase in the injection level causes an increase in the annealing factor. However, this study shows that this seemingly different behavior can be correlated on the basis of the hole-to-electron ratios of the different material types and resistivities. Annealing measurements performed in the temperature range from 180°to 300°K reaffirm the 0.3 eV activation energy previously found in P-type silicon and establish a value of 0.17 eV for N-type silicon.     

Application of Silicon Damage to Neutron Exposure Measurement

A technique is described for using the damage in silicon to measure neutron exposure in Radiation Damage Units (RDUs) with transistors called Radiation Damage Monitors (RDMs). The technique is useful in measuring the damage gradients across experiments and in determining the relative damage effect of a neutron environment. Two calibration procedures are described, as are the operating characteristics and use procedures for five transistor RDMs to cover the exposure range from 1011 to 1015 n/cm2.     

一种可测低能γ和X射线的高纯n型硅探测器

采用蒸发金、钯和离子注入硼作势垒接触,低温扩散锂制备欧姆接触的方法,制成性能良好的低能γ和X射线高纯硅探测器。介绍其制作方法和性能。探测器有效面积为14.5mm~2,厚度3.3mm。在液氮温度下对~(55)Fe 5.9kev X射线的最佳能量分辨率为162eV,对~(241)Am59.5keV低能γ射线的最佳能量分辨率为373eV。同时对三种不同制作方法所得的高纯硅探测器和Si(Li)X射线探测器进行了对比。